Friday, 21 May 2010
ENGINE MANAGEMENT SYSTEM - MPi
The Engine Control Module (ECM) monitors the conditions required for optimum combustion of fuel in the cylinder through sensors located at strategic points around the engine. From these sensor inputs, the engine control module can adjust the fuel quantity and timing of the fuel being delivered to the cylinders.
The main features are as follows:
- A single ECM controls the fuel injection system and the ignition system. The ECM incorporates short circuit protection and can store intermittent faults on certain inputs. TestBook can interrogate the ECM for these stored faults.
- The ECM is electronically immobilised preventing the engine from being started unless it receives a coded signal from the anti-theft control unit.
- In conjunction with the throttle position sensor the ECM uses the speed/density method of air flow measurement to calculate fuel delivery. This method measures the inlet air temperature and inlet manifold pressure and assumes that the engine is a calibrated vacuum pump, with its characteristics stored in the ECM, it can then determine the correct amount of fuel to be injected.
- A separate diagnostic connector, located on the passenger compartment fusebox, allows engine tuning or fault diagnosis to be carried out using TestBook without disconnecting the ECM harness multiplug.
- The ECM harness multiplug incorporates specially plated pins to minimise oxidation and give improved reliability.
- The ECM controls the operation of the radiator and air conditioning cooling fans, based on signals received from the engine coolant temperature sensor and trinary switch. The engine compartment cooling fan receives signals from the ambient air temperature sensor. If a high engine coolant temperature is detected the ECM will prevent the air conditioning system from operating.
- If certain system inputs fail, the ECM implements a back-up facility to enable the system to continue functioning, although at a reduced level of performance.
IGNITION SYSTEM - MPi MEMS 1.9
The ECM determines the optimum ignition timing based on the signals from the following sensors:
1. Crankshaft position sensor - Engine speed and crankshaft position
2. Manifold absolute pressure sensor - Engine load
3. Engine coolant temperature sensor - Engine temperature
4. Manifold absolute pressure sensor - Throttle pedal released
The engine management system uses no centrifugal or vacuum advance. Timing is controlled by the ECM which is energised by the main relay within the relay module. Spark distribution is achieved by means of a rotor arm and distributor mounted at the No.4 cylinder end of the inlet camshaft.
BASIC IGNITION TIMING - MPi
Crankshaft position sensor
The speed and position of the engine is detected by the crankshaft position (CKP) sensor which is bolted to, and projects through, the engine adapter plate adjacent to the flywheel. The CKP sensor is an inductive sensor consisting of a bracket mounted body containing a coil and a permanent magnet which provides a magnetic field. The CKP sensor is situated so that an air gap exists between it and the flywheel. Air gap distance is critical for correct operation. The flywheel incorporates a reluctor ring which consists of 32 poles spaced at 1°intervals, with 4 missing poles at °, 12°, 18° and 31°. The missing poles inform the ECM when to operate the groups of injectors. When the flywheel rotates, as a pole passes the CKP sensor it disturbs the magnetic field inducing a voltage pulse in the coil. This pulse is transmitted to the ECM. By calculating the number of pulses that occur within a given time, the ECM can determine the engine speed. The output from the CKP sensor when used in conjunction with that from the manifold absolute pressure sensor provides idle stabilisation and reference for injection timing.
Manifold absolute pressure sensor
The manifold absolute pressure (MAP) sensor is located within the ECM and detects manifold pressure via a hose connected to the inlet manifold. The MAP sensor converts pressure variations into graduated electrical signals which can be read by the ECM. Increases and decreases in the manifold pressure provide the ECM with an accurate representation of the load being placed on the engine allowing the ECM to adjust the quantity of fuel being injected and the ignition timing to achieve optimum fuelling of the engine.
IGNITION TIMING COMPENSATION - MPi
Engine coolant temperature sensor
The engine coolant temperature (ECT) sensor is a thermistor (a temperature dependent resistor), i.e. the voltage output varies in proportion to temperature. The ECT sensor is located in the front of the coolant outlet elbow and can be distinguished from the gauge sensor by its brown colour. The ECM constantly monitors this signal and uses the information to provide optimum driveability and emissions by advancing or retarding the ignition timing.
Idle speed control
With the throttle pedal released and the engine at idle, the ECM uses the fast response of ignition timing to maintain idle stabilisation. When loads are placed on or removed from the engine, the ECM senses the change in engine speed, and in conjunction with adjusting the idle air control (IAC) valve, advances or retards the ignition timing to maintain a specified idle speed. When load is removed from the engine, the IAC valve returns to its original position and the ignition timing returns to the idle setting.
NOTE: Due to the sensitivity of this system the ignition timing will be constantly changing at idle speed.
IGNITION COMPONENTS -MPi
Ignition coil
The coil for the programmed ignition system is mounted on the back of the engine. The coil has a lower primary winding resistance (0.63 to 0.77 ohms at 2°C) than a coil in a conventional ignition system. This allows the full h.t. output to be reached faster and so makes the coil operation more consistent throughout the engine speed range.
Distributor cap and rotor arm
1. Distributor cap
2. Rotor arm
3. Retaining screw
4. Anti-flash shield
The distributor cap, carrying a central carbon brush and four h.t. lead pick-ups, is located at the No.4 cylinder end of the inlet camshaft and surrounds the rotor arm. The rotor arm is secured by a retaining screw to a 'D' shaped stub shaft, which is press fitted into a vibration absorbing bush in the camshaft, and is protected from oil contamination by an anti-flash shield which incorporates an oil drain.
FUEL SYSTEM - MPi
Engine Control Module (ECM)
The Modular Engine Management System (MEMS) is controlled by an ECM mounted on the bulkhead in the engine compartment. The ECM is an adaptive unit which over a period of time learns the load and wear characteristics of the engine it controls. The ECM remembers and updates two main engine requirements when the engine is running at normal operating temperature:
1. The position of the idle air control (IAC) valve required to achieve a specified idle speed. This is then used as a reference for IAC valve movement to achieve idle speed under all load conditions.
2. The fuelling change or offset required to achieve a set oxygen sensor output indicating an air fuel ratio of 14.7:1. This allows the system to provide the correct fuelling without having to apply excessive adjustments to the fuelling which can adversely affect the emissions and driveability.
NOTE: After fitting a different ECM, TestBook will be required to reprogram the ECM with the code from the anti-theft control unit and to perform a full engine tune procedure.
The ECM inputs and outputs are shown in the following table.
INPUTS
Crankshaft position sensor
Ambient air temperature sensor
Manifold absolute pressure sensor
Engine coolant temperature sensor
Intake air temperature sensor
Heated oxygen sensor
Throttle position sensor
Diagnostic input
Battery supply
Starter signal
Earth supply
Anti-theft control unit
A/C Trinary switch
OUTPUTS
Ignition coil
Injectors
Idle air control valve
ECM Fuel pump relay
Diagnostic connector
Heated oxygen sensor relay
Main relay
Cooling fans
Air conditioning fans
Engine bay fans
Purge valve
Intake air temperature sensor
The intake air temperature (IAT) sensor is located in the side of the inlet manifold. The IAT sensor is of the negative temperature coefficient (NTC) type, designed to reduce its resistance with increasing temperature. The ECM receives a signal from the IAT sensor proportional to the temperature of the intake air. When this signal is used in conjunction with the signal from the manifold absolute pressure sensor. The ECM calculates the volume of oxygen in the air and adjusts the quantity of fuel being injected, to achieve optimum fuelling of the engine.
Injectors
The four fuel injectors are fitted between the pressurised fuel rail and inlet manifold. Each injector comprises a solenoid operated needle valve and a specially designed nozzle to ensure good fuel atomisation. The injectors are controlled in grouped mode with 2 & 3 being grouped and 1 & 4 being grouped, with the injectors in each group being operated alternatively. The ECM determines when to operate the injectors based on the signal it receives from the crankshaft position sensor. The ECM provides an earth signal for the period the injectors are required to be open, the injector solenoids are energised and fuel is sprayed into the inlet manifold onto the back of the inlet valves. The ECM carefully meters the amount of fuel injected by adjusting the injector opening period (pulse width). During cranking, when the engine speed is below approximately 400 rev/min, the ECM increases the injector pulse width to aid starting. The amount of increase depends upon engine coolant temperature. To prevent flooding, the ECM periodically inhibits the operation of the injectors.
Throttle housing
The throttle housing is located between the inlet manifold and air intake hose and is sealed to the manifold by an O-ring. The throttle housing incorporates a throttle disc which is connected to the throttle pedal via the throttle lever and a cable. There are two breather pipes connected to the throttle housing, one either side of the throttle disc. When the engine is running with the throttle disc open, both pipes are subject to manifold depression and draw crankcase fumes into the manifold. When the throttle disc is closed, only the pipe on the inlet manifold side of the disc is subject to manifold depression. This pipe incorporates a restrictor to prevent engine oil being drawn into the engine by the substantially greater manifold depression. Mounted on the throttle housing are the throttle position sensor and idle air control valve.
Throttle position sensor
The throttle position (TP) sensor is a potentiometer attached to the throttle housing and is directly coupled to the throttle disc. The TP sensor is non-adjustable. Closed throttle is detected by the TP sensor which initiates idle speed control via the idle air control valve. The ECM supplies the TP sensor with a 5 volt supply and an earth path. The TP sensor returns a signal proportional to throttle disc position. Throttle disc movement causes voltage across the TP sensor to vary. The ECM calculates the rate of change of the voltage signal in positive (acceleration) or negative (deceleration) directions. From this the ECM can determine the required engine speed, rate of acceleration or rate of deceleration and apply acceleration enrichment, deceleration fuel metering or over-run fuel cut-off.
Idle air control valve
The idle air control (IAC) valve is mounted on the inlet manifold and controlled by the ECM. The IAC valve opens a pintle valve situated in an air passage in the throttle housing, allowing air to bypass the throttle disc and flow straight into the inlet manifold. By changing the amount the IAC valve is open the ECM can control engine idle speed and cold start air flow requirements by adjusting the flow of air in the passage. During cold starting the ECM indexes the IAC valve open slightly to provide a level of fast idle, dependent on engine coolant temperature. As the engine warms, fast idle is gradually decreased until normal operating temperature is reached. The position of the IAC valve can be checked using TestBook and should be within the range of 20 to 40 steps when the engine is running. If it is identified as being outside this range it can be adjusted to within range using TestBook. This ensures that the IAC valve is at the optimum position within its range for providing further movement to compensate for changes in engine load or temperature in accordance with signals from the ECM.
NOTE: The position of the throttle disc is preset during manufacture and the throttle position setting screw MUST NOT be adjusted.
Engine management relay module
The relay module is located on the bulkhead in the engine compartment behind the engine control module. The relay module contains the following relays:
- Main relay - energised when the ignition is switched on and supplies power to the ECM.
- Fuel pump relay - energised by the ECM for a short period when the ignition is switched on, during cranking and while the engine is running. - Starter relay - energised by the cranking signal from the ignition switch.
- Heated oxygen sensor relay - energised by the ECM and supplies current to the heated oxygen sensor element.
Fuel pump
The electric fuel pump is located inside the fuel tank and is energised by the ECM via the fuel pump relay in the relay module and the fuel cut-off inertia switch. The fuel pump delivers more fuel than the maximum load requirement for the engine, pressure is therefore maintained in the fuel system under all conditions.
Fuel pressure regulator
The pressure regulator is a mechanical device controlled by manifold depression and is mounted on one end of the fuel rail. The regulator ensures that fuel rail pressure is maintained at a constant pressure difference to that in the inlet manifold, as manifold depression increases the regulated fuel pressure is reduced in direct proportion. When pressure exceeds the regulator setting, excess fuel is returned to the fuel tank swirl pot which contains the fuel pump pick-up.
Inertia fuel shut-off switch
The electrical circuit for the fuel pump incorporates an inertia fuel shut-off (IFS) switch which, in the event of a sudden deceleration, breaks the circuit to the fuel pump preventing fuel being delivered to the engine. The IFS switch is situated in the engine compartment next to the ECM, and must be reset by pressing the rubber top before the engine can be restarted.
WARNING: ALWAYS check for fuel leaks and the integrity of fuel system
connections before resetting the switch.
Diagnostic connector
A diagnostic connector, located on the passenger compartment fusebox, allows engine tuning or fault diagnosis to be carried out using TestBook without disconnecting the ECM harness multiplug.
Heated oxygen sensor
The modular engine management system operates a closed loop emission system to ensure the most efficient level of exhaust gas conversion. Amend text and include subscript commands A heated oxygen sensor (HO2S) fitted in the exhaust manifold monitors the exhaust gases. It then supplies a small voltage proportional to exhaust oxygen content to the ECM. As the air/fuel mixture weakens, the exhaust oxygen content increases and so the voltage to the ECM decreases. If the mixture becomes richer so the oxygen content decreases and the voltage increases. From this signal the ECM can determine the air/fuel mixture being delivered to the engine, and can adjust the duration the injectors are open to maintain the ratio necessary for efficient gas conversion by the catalyst. The HO2S has an integral heating element to ensure an efficient operating temperature is quickly reached from cold. The electrical supply to the heater element is controlled by the ECM via the HO2S relay in the relay module.
Acceleration enrichment
When the throttle pedal is depressed, the ECM receives a rising voltage from the throttle position sensor and detects a rise in manifold pressure from the manifold absolute pressure sensor. The ECM provides additional fuel by increasing the normal injector pulse width and also provides a small number of extra additional pulses on rapid throttle openings.
Over-run fuel cut-off
The ECM implements over-run fuel cut-off when the engine speed is above 2000 rev/min with engine at normal operating temperature and the throttle position sensor in the closed position, i.e. the vehicle is "coasting" with the throttle pedal released. The ECM indexes the idle air control valve open slightly to increase the air flow through the engine to maintain a constant manifold depression to keep emissions low. Fuel is progressively reinstated as the throttle position sensor is opened.
Over-speed fuel cut-off
To prevent damage at high engine speeds the ECM will implement fuel cut-off at engine speeds above 7000 rev/min by inhibiting the earth path for the injectors, as engine speed falls to 6990 rev/min, fuel is progressively reinstated.
Ignition switch off
When the ignition is switched off, the ECM will keep the main relay energised for approximately 30 seconds while it drives the idle air control valve to its power down position, ready for the next engine start. The ECM then monitors the engine bay temperature using the ambient air temperature sensor. If the temperature is above a certain limit, the ECM will drive the engine bay fan for 8 minutes, and will then power down. If the engine bay temperature is below the limit the ECM will power down after 10 seconds. Engine compartment ambient air temperature sensor The ECM monitors the engine compartment temperature using the ambient air temperature sensor. When the temperature exceeds a certain limit, the engine bay fan relay is energised to run the fan. If the temperature continues to rise, and exceeds another higher limit, the engine bay warning lamp (in the instrument pack) is illuminated. If the ambient air temperature sensor fails, the engine bay fan will run while the ignition is on and the warning lamp will be permanently lit.
1. Air cleaner element
2. Throttle disc
3. Idle air control valve
4. Inlet manifold
5. Injector
6. Evaporative emission cannister, purge valve
7. Evaporative emission cannister
8. Engine Control Module (ECM)
9. Fuel trap - green connection to ECM
Intake air is drawn into the throttle body through an air filter element. Incorporated in the throttle body are the throttle disc and the throttle position sensor. Air passes from the throttle body to the inlet manifold where it is mixed with fuel injected by the injectors before the mixture is drawn into the combustion chamber. Inlet manifold depression is measured via a hose, by the MAP sensor which is incorporated in the ECM. A signal from the MAP sensor is used by the ECM to calculate the amount of fuel delivered by the injectors.
Glossary of automotive 2
OCTANE RATING: A number indicating the quality of gasoline based on its ability to resist knock. The higher the number, the better the quality. Higher compression engines require higher octane gas.OEM: Original Equipment Manufactured. OEM equipment is that furnished standard by the manufacturer.
OFFSET: The distance between the vertical center of the wheel and the mounting surface at the lugs. Offset is positive if the center is outside the lug circle; negative offset puts the center line inside the lug circle.
OHM: The unit used to measure the resistance of conductor-to-electrical flow. One ohm is the amount of resistance that limits current flow to one ampere in a circuit with one volt of pressure.
OHMMETER: An instrument used for measuring the resistance, in ohms, in an electrical circuit.
OSCILLOSCOPE: A piece of test equipment that shows electric impulses as a pattern on a screen. Engine performance can be analyzed by interpreting these patterns.
O2 SENSOR: See oxygen sensor.
OUTPUT SHAFT: The shaft which transmits torque from a device, such as a transmission.
OVERDRIVE: (1.) A device attached to or incorporated in a transmission that allows the engine to turn less than one full revolution for every complete revolution of the wheels. The net effect is to reduce engine rpm, thereby using less fuel. A typical overdrive gear ratio would be .87:1, instead of the normal 1:1 in high gear. (2.) A gear assembly which produces more shaft revolutions than that transmitted to it.
OVERHEAD CAMSHAFT (OHC): An engine configuration in which the camshaft is mounted on top of the cylinder head and operates the valve either directly or by means of rocker arms.
OVERHEAD VALVE (OHV): An engine configuration in which all of the valves are located in the cylinder head and the camshaft is located in the cylinder block. The camshaft operates the valves via lifters and pushrods.
OVERSTEER: The tendency of some cars, when steering into a turn, to over-respond or steer more than required, which could result in excessive slip of the rear wheels. Opposite of understeer.
OXIDES OF NITROGEN: See nitrogen oxide (NOx).
OXYGEN SENSOR: Used with a feedback system to sense the presence of oxygen in the exhaust gas and signal the computer which can use the voltage signal to determine engine operating efficiency and adjust the air/fuel ratio.
PARK NEUTRAL SAFETY SWITCH: On vehicles with automatic transmissions, a neutral safety switch (often referred to by various names by the different manufacturers, such as: transmission range sensor, neutral safety switch, park/neutral switch, etc.) on the side of the transmission is wired to the relay or solenoid. Its function is to prevent activation of the starter (by creating an open circuit) when the transmission is in any gear other than P (park) or N (neutral). The vehicle can only be started in P or N. Most manual transmission vehicles have a clutch switch to prevent starting the vehicle unless the clutch is depressed.
PARTS WASHER: A basin or tub, usually with a built-in pump mechanism and hose used for circulating chemical solvent for the purpose of cleaning greasy, oily and dirty components.
PART-TIME FOUR-WHEEL DRIVE: A system that is normally in the two-wheel drive mode and only runs in four-wheel drive when the system is manually engaged because more traction is desired. Two or four-wheel drive is normally selected by a lever to engage the front axle, but if locking hubs are used, these must also be manually engaged in the Lock position. Otherwise, the front axle will not drive the front wheels.
PASSIVE RESTRAINT: Safety systems such as air bags or automatic seat belts which operate with no action required on the part of the driver or passenger. Mandated by Federal regulations on all cars sold in the U.S. after 1990.
PAYLOAD: The weight the car is capable of carrying in addition to its own weight. Payload includes weight of the driver, passengers and cargo, but not coolant, fuel, lubricant, spare tire, etc.
PCM: Powertrain control module. See Electronic Control Unit (ECU).
PCV VALVE: A valve usually located in the rocker cover that vents crankcase vapors back into the engine to be reburned.
PERCOLATION: A condition in which the fuel actually "boils" due to excessive heat. Percolation prevents proper atomization of the fuel causing rough running.
PICK-UP COIL: The coil in which voltage is induced in an electronic ignition.
PING: A metallic rattling sound produced by the engine during acceleration. It is usually due to incorrect ignition timing or a poor grade of gasoline.
PINION: The smaller of two gears. The rear axle pinion drives the ring gear which transmits motion to the axle shafts.
PISTON RING: An open-ended ring which fits into a groove on the outer diameter of the piston. Its chief function is to form a seal between the piston and cylinder wall. Most automotive pistons have three rings: two for compression sealing; one for oil sealing.
PITMAN ARM: A lever which transmits steering force from the steering gear to the steering linkage.
PLY RATING: A rating given a tire which indicates strength (but not necessarily actual plies). A two-ply/four-ply rating has only two plies, but the strength of a four-ply tire.
POLARITY: Indication (positive or negative) of the two poles of a battery.
POWER-TO-WEIGHT RATIO: Ratio of horsepower to weight of car.
POWERTRAIN: See Drivetrain.
Ppm: Parts per million; unit used to measure exhaust emissions.
PREIGNITION: Early ignition of fuel in the cylinder, sometimes due to glowing carbon deposits in the combustion chamber. Preignition can be damaging since combustion takes place prematurely.
PRELOAD: A predetermined load placed on a bearing during assembly or by adjustment.
PRESS FIT: The mating of two parts under pressure, due to the inner diameter of one being smaller than the outer diameter of the other, or vice versa; an interference fit.
PRESSURE PLATE: A spring-loaded plate (part of the clutch) that transmits power to the driven (friction) plate when the clutch is engaged.
PRIMARY CIRCUIT: The low voltage side of the ignition system which consists of the ignition switch, ballast resistor or resistance wire, bypass, coil, electronic control unit and pick-up coil as well as the connecting wires and harnesses.
PROFESSIONAL TECHNICIAN: A repair technician that has been properly trained in a vehicle’s systems. Usually affiliated with ASE or other certification system. This technician will also have the proper tools to diagnose and repair your vehicle.
PROFILE: Term used for tire measurement (tire series), which is the ratio of tire height to tread width.
Psi: Pounds per square inch; a measurement of pressure.
PUSHROD: A steel rod between the hydraulic valve lifter and the valve rocker arm in overhead valve (OHV) engines.
QUARTER PANEL: General term used to refer to a rear fender. Quarter panel is the area from the rear door opening to the tail light area and from rear wheelwell to the base of the trunk and roof-line.
RACE: The surface on the inner or outer ring of a bearing on which the balls, needles or rollers move.
RACK AND PINION: A type of automotive steering system using a pinion gear attached to the end of the steering shaft. The pinion meshes with a long rack attached to the steering linkage.
RADIAL TIRE: Tire design which uses body cords running at right angles to the center line of the tire. Two or more belts are used to give tread strength. Radials can be identified by their characteristic sidewall bulge.
RADIATOR: Part of the cooling system for a water-cooled engine, mounted in the front of the car and connected to the engine with rubber hoses. Through the radiator, excess combustion heat is dissipated into the atmosphere through forced convection using a water and glycol based mixture that circulates through, and cools, the engine.
REAR MAIN OIL SEAL: A synthetic or rope-type seal that prevents oil from leaking out of the engine past the rear main crankshaft bearing.
RECALL: When a manufacturer recalls vehicles it has manufactured back to the dealership for specific repairs related to unplanned mechanical problems and/or safety issues. Recalls are usually voluntary and are made in conjunction with regulatory control of the National Highway Traffic Safety Agency (NHTSA). They can originate with the manufacturer or with the NHTSA. Repairs performed under a recall are usually free to the consumer.
RECIRCULATING BALL: Type of steering system in which recirculating steel balls occupy the area between the nut and worm wheel, causing a reduction in friction.
RECTIFIER: A device (used primarily in alternators) that permits electrical current to flow in one direction only.
REFRIGERANT 12 (R-12) or 134 (R-134): The generic name of the refrigerant used in automotive air conditioning systems.
REGULATOR: A device which maintains the amperage and/or voltage levels of a circuit at predetermined values.
RELAY: A switch which automatically opens and/or closes a circuit.
RELUCTOR: A wheel that rotates inside the distributor and triggers the release of voltage in an electronic ignition.
RESIN: A liquid plastic used in body work.
RESISTANCE: The opposition to the flow of current through a circuit or electrical device, and is measured in ohms. Resistance is equal to the voltage divided by the amperage.
RESISTOR SPARK PLUG: A spark plug using a resistor to shorten the spark duration. This suppresses radio interference and lengthens plug life.
RESISTOR: A device, usually made of wire, which offers a preset amount of resistance in an electrical circuit.
RETARD: Setting the ignition timing so that spark occurs later (fewer degrees before TDC).
RING GEAR: The name given to a ring-shaped gear attached to a differential case, or affixed to a flywheel or as part of a planetary gear set.
ROCKER ARM: A lever which rotates around a shaft pushing down (opening) the valve with an end when the other end is pushed up by the pushrod. Spring pressure will later close the valve.
ROCKER PANEL: The body panel below the doors between the wheel openings.
ROLLER BEARING: A bearing made up of hardened inner and outer races between which hardened steel rollers move.
ROTOR: (1.) The disc-shaped part of a disc brake assembly, upon which the brake pads bear; also called brake disc. (2.) The device mounted atop the distributor shaft, which passes current to the distributor cap tower contacts.
ROTARY ENGINE: See Wankel engine.
RPM: Revolutions per minute (usually indicates engine speed).
RUN-ON: Condition when the engine continues to run, even when the key is turned off. See dieseling.
SEALED BEAM: An automotive headlight. The lens, reflector and filament form a single unit.
SEATBELT INTERLOCK: A system whereby the car cannot be started unless the seatbelt is buckled.
SECONDARY CIRCUIT: The high voltage side of the ignition system, usually above 20,000 volts. The secondary includes the ignition coil, coil wire, distributor cap and rotor, spark plug wires and spark plugs.
SEMI-FLOATING AXLE: In this design, a wheel is attached to the axle shaft, which takes both drive and cornering loads. Almost all solid axle passenger cars and light trucks use this design.
SENDING UNIT: A mechanical, electrical, hydraulic or electromagnetic device which transmits information to a gauge.
SENSOR: Any device designed to measure engine operating conditions or ambient pressures and temperatures. Usually electronic in nature and designed to send a voltage signal to an on-board computer, some sensors may operate as a simple on/off switch or they may provide a variable voltage signal (like a potentiometer) as conditions or measured parameters change.
SERPENTINE BELT: An accessory drive belt, with small multiple v-ribs, routed around most or all of the engine-powered accessories such as the alternator and power steering pump. Usually both the front and the back side of the belt come into contact with various pulleys.
SHEATH: The outer casing for clutch or brake cables.
SHIM: Spacers of precise, predetermined thickness used between parts to establish a proper working relationship.
SHIMMY: Vibration (sometimes violent) in the front end caused by misaligned front end, out of balance tires or worn suspension components.
SHORT CIRCUIT: An electrical malfunction where current takes the path of least resistance to ground (usually through damaged insulation). Current flow is excessive from low resistance resulting in a blown fuse.
SINGLE OVERHEAD CAMSHAFT: See overhead camshaft.
SKIDPLATE: A metal plate attached to the underside of the body to protect the fuel tank, transfer case or other vulnerable parts from damage.
SLAVE CYLINDER: In automotive use, a device in the hydraulic clutch system which is activated by hydraulic force, disengaging the clutch.
SLUDGE: Thick, black deposits in engine formed from dirt, oil, water, etc. It is usually formed in engines when oil changes are neglected.
SNAP RING: A circular retaining clip used inside or outside a shaft or part to secure a shaft, such as a floating wrist pin.
SOHC: Single overhead camshaft.
SOLENOID: An electrically operated, magnetic switching device.
SPARK PLUG: A device screwed into the combustion chamber of a spark ignition engine. The basic construction is a conductive core inside of a ceramic insulator, mounted in an outer conductive base. An electrical charge from the spark plug wire travels along the conductive core and jumps a preset air gap to a grounding point or points at the end of the conductive base. The resultant spark ignites the fuel/air mixture in the combustion chamber.
SPECIFIC GRAVITY (BATTERY): The relative weight of liquid (battery electrolyte) as compared to the weight of an equal volume of water.
SPLINES: Ridges machined or cast onto the outer diameter of a shaft or inner diameter of a bore to enable parts to mate without rotation.
SPONGY PEDAL: A soft or spongy feeling when the brake pedal is depressed. It is usually due to air in the brake lines.
SPRUNG WEIGHT: The weight of a car supported by the springs.
SRS: Supplemental restraint system
STABILIZER (SWAY) BAR: A bar linking both sides of the suspension. It resists sway on turns by taking some of the added load from one wheel and putting it on the other.
STARTER: A high-torque electric motor used for the purpose of starting the engine, typically through a high ratio geared drive connected to the flywheel ring gear.
STEERING GEOMETRY: Combination of various angles of suspension components (caster, camber, toe-in); roughly equivalent to front end alignment.
STRAIGHT WEIGHT: Term designating motor oil as suitable for use within a narrow range of temperatures. Outside the narrow temperature range, its flow characteristics will not adequately lubricate.
STROKE: The distance the piston travels from bottom dead center to top dead center.
SUPERCHARGER: An air pump driven mechanically by the engine through belts, chains, shafts or gears from the crankshaft. Two general types of supercharger are the positive displacement and centrifugal types, which pump air in direct relationship to the speed of the engine.
SUPPLEMENTAL RESTRAINT SYSTEM: See air bag.
SYNCHROMESH: A manual transmission that is equipped with devices (synchronizers) that match the gear speeds so that the transmission can be downshifted without clashing gears.
SYNTHETIC OIL: Non-petroleum based oil.
TAMPERING: Used in conjunction with a vehicles emission control system. Tampering is used to describe any alterations to the original design of the vehicles emission control system.
TAMPERING INSPECTION: An inspection done by State or Local authorities to determine if a vehicle's emission control system has been tampered with.
TACHOMETER: A device used to measure the rotary speed of an engine, shaft, gear, etc., usually in rotations per minute.
TDC: Top dead center. The exact top of the piston's stroke.
THERMOSTAT: A valve, located in the cooling system of an engine, which is closed when cold and opens gradually in response to engine heating, controlling the temperature of the coolant and rate of coolant flow.
THROW-OUT BEARING: As the clutch pedal is depressed, the throwout bearing moves against the spring fingers of the pressure plate, forcing the pressure plate to disengage from the driven disc.
TIE ROD: A rod connecting the steering arms. Tie rods have threaded ends that are used to adjust toe-in.
TIMING BELT: A square-toothed, reinforced rubber belt that is driven by the crankshaft and operates the camshaft.
TIMING CHAIN: A roller chain that is driven by the crankshaft and operates the camshaft.
TIRE ROTATION: Moving the tires from one position to another to make the tires wear evenly.
TOE-IN (OUT): A term comparing the extreme front and rear of the front tires. Closer together at the front is toe-in; farther apart at the front is toe-out.
TOP DEAD CENTER (TDC): The point at which the piston reaches the top of its travel on the compression stroke.
TORQUE: Measurement of turning or twisting force, expressed as foot-pounds or inch-pounds.
TORQUE CONVERTER: A turbine used to transmit power from a driving member to a driven member via hydraulic action, providing changes in drive ratio and torque. In automotive use, it links the driveplate at the rear of the engine to the automatic transmission.
TORSION BAR SUSPENSION: Long rods of spring steel which take the place of springs. One end of the bar is anchored and the other arm (attached to the suspension) is free to twist. The bars' resistance to twisting causes springing action.
TRACK: Distance between the centers of the tires where they contact the ground.
TRACTION CONTROL: A control system that prevents the spinning of a car's drive wheels when excess power is applied.
TRANSAXLE: A single housing containing the transmission and differential. Transaxles are usually found on front engine/front wheel drive or rear engine/rear wheel drive cars.
TRANSDUCER: A device used to change a force into an electrical signal.
TRANSFER CASE: A gearbox driven from the transmission that delivers power to both front and rear driveshafts in a four-wheel drive system. Transfer cases usually have a high and low range set of gears, used depending on how much pulling power is needed.
TRANSISTOR: A semi-conductor component which can be actuated by a small voltage to perform an electrical switching function.
TREAD WEAR INDICATOR: Bars molded into the tire at right angles to the tread that appear as horizontal bars when1/16 th in. of tread remains.
TREAD WEAR PATTERN: The pattern of wear on tires which can be "read" to diagnose problems in the front suspension.
TSB: Acronym for Technical Service Bulletin. This bulletin is produced by the vehicle manufacturer and alerts automotive technicians about specific service problem areas, repair procedures, and new service techniques for a vehicle.
TUNE-UP: A regular maintenance function, usually associated with the replacement and adjustment of parts and components in the electrical and fuel systems of a car for the purpose of attaining optimum performance.
TURBOCHARGER: An exhaust driven pump which compresses intake air and forces it into the combustion chambers at higher than atmospheric pressures. The increased air pressure allows more fuel to be burned and results in increased horsepower being produced.
TURN OVER: Synonymous with "cranks over", the action of the engine internal components rotating during the starting cycle. This is what happens when you turn the key before the engine starts.
U-JOINT (UNIVERSAL JOINT): A flexible coupling in the drive train that allows the driveshafts or axle shafts to operate at different angles and still transmit rotary power.
ULTRAVIOLET LIGHT: A light used in conjunction with a fluorescent dye to detect leaks in the engine, transmission or cooling system.
UNDER LOAD: Used to describe the condition of a vehicle when climbing a steep incline or hill. When the vehicle is placed under a higher than normal amount of load when carrying excessive cargo.
UNDERSTEER: The tendency of a car to continue straight ahead while negotiating a turn.
UNIT BODY: Design in which the car body acts as the frame.
UNLEADED FUEL: Fuel which contains no lead (a common gasoline additive). The presence of lead in fuel will destroy the functioning elements of a catalytic converter, making it useless.
UNSPRUNG WEIGHT: The weight of car components not supported by the springs (wheels, tires, brakes, rear axle, control arms, etc.).
VACUUM ADVANCE: A device which advances the ignition timing in response to increased engine vacuum.
VACUUM MODULATOR: A device used to control the transmission shift points based on the amount of load placed on the engine.
VACUUM GAUGE: An instrument used to measure the presence of vacuum in a chamber.
VALVE: A device which control the pressure, direction of flow or rate of flow of a liquid or gas.
VALVE CLEARANCE: The measured gap between the end of the valve stem and the rocker arm, cam lobe or follower that activates the valve.
VALVE GUIDES: The guide through which the stem of the valve passes. The guide is designed to keep the valve in proper alignment.
VALVE LASH (CLEARANCE): The operating clearance in the valve train.
VALVE STEM SEALS: Synthetic rubber seals that are used to control the oil that lubricates the valve stems in the valve guides. Worn valve stem seals can cause blue smoke from the exhaust when first starting the engine.
VALVE TRAIN: The system that operates intake and exhaust valves, consisting of camshaft, valves and springs, lifters, pushrods and rocker arms.
VAPOR LOCK: Boiling of the fuel in the fuel lines due to excess heat. This will interfere with the flow of fuel in the lines and can completely stop the flow. Vapor lock normally only occurs in hot weather.
VARNISH: Term applied to the residue formed when gasoline gets old and stale.
VCM: See Electronic Control Unit (ECU).
VISCOSITY: The ability of a fluid to flow. The lower the viscosity rating, the easier the fluid will flow. 10 weight motor oil will flow much easier than 40 weight motor oil.
VOLT: Unit used to measure the force or pressure of electricity. It is defined as the pressure needed to move one amp through a resistance of one ohm.
VOLTAGE REGULATOR: A device that controls the current output of the alternator or generator.
VOLTMETER: An instrument used for measuring electrical force in units called volts. Voltmeters are always connected parallel with the circuit being tested.
WANKEL ENGINE: An engine which uses no pistons. In place of pistons, triangular-shaped rotors revolve in specially shaped housings.
WATER PUMP: A belt driven component of the cooling system that mounts on the engine, circulating the coolant under pressure.
WEAR INDICATORS: A metal tab mounted on disc brake pads that touch the brake rotor when the brake linings need replacement.
WHEEL ALIGNMENT: Inclusive term to describe the front end geometry (caster, camber, toe-in/out).
WHEEL CYLINDER: Found in the automotive drum brake assembly, it is a device, actuated by hydraulic pressure, which, through internal pistons, pushes the brake shoes outward against the drums.
WHEEL WEIGHT: Small weights attached to the wheel to balance the wheel and tire assembly. Out-of-balance tires quickly wear out and also give erratic handling when installed on the front.
WHEELBASE: Distance between the center of front wheels and the center of rear wheels.
OFFSET: The distance between the vertical center of the wheel and the mounting surface at the lugs. Offset is positive if the center is outside the lug circle; negative offset puts the center line inside the lug circle.
OHM: The unit used to measure the resistance of conductor-to-electrical flow. One ohm is the amount of resistance that limits current flow to one ampere in a circuit with one volt of pressure.
OHMMETER: An instrument used for measuring the resistance, in ohms, in an electrical circuit.
Figure 21 Checking resistance using an ohmmeter  |
O2 SENSOR: See oxygen sensor.
OUTPUT SHAFT: The shaft which transmits torque from a device, such as a transmission.
OVERDRIVE: (1.) A device attached to or incorporated in a transmission that allows the engine to turn less than one full revolution for every complete revolution of the wheels. The net effect is to reduce engine rpm, thereby using less fuel. A typical overdrive gear ratio would be .87:1, instead of the normal 1:1 in high gear. (2.) A gear assembly which produces more shaft revolutions than that transmitted to it.
OVERHEAD CAMSHAFT (OHC): An engine configuration in which the camshaft is mounted on top of the cylinder head and operates the valve either directly or by means of rocker arms.
OVERHEAD VALVE (OHV): An engine configuration in which all of the valves are located in the cylinder head and the camshaft is located in the cylinder block. The camshaft operates the valves via lifters and pushrods.
OVERSTEER: The tendency of some cars, when steering into a turn, to over-respond or steer more than required, which could result in excessive slip of the rear wheels. Opposite of understeer.
OXIDES OF NITROGEN: See nitrogen oxide (NOx).
OXYGEN SENSOR: Used with a feedback system to sense the presence of oxygen in the exhaust gas and signal the computer which can use the voltage signal to determine engine operating efficiency and adjust the air/fuel ratio.
PARK NEUTRAL SAFETY SWITCH: On vehicles with automatic transmissions, a neutral safety switch (often referred to by various names by the different manufacturers, such as: transmission range sensor, neutral safety switch, park/neutral switch, etc.) on the side of the transmission is wired to the relay or solenoid. Its function is to prevent activation of the starter (by creating an open circuit) when the transmission is in any gear other than P (park) or N (neutral). The vehicle can only be started in P or N. Most manual transmission vehicles have a clutch switch to prevent starting the vehicle unless the clutch is depressed.
PARTS WASHER: A basin or tub, usually with a built-in pump mechanism and hose used for circulating chemical solvent for the purpose of cleaning greasy, oily and dirty components.
PART-TIME FOUR-WHEEL DRIVE: A system that is normally in the two-wheel drive mode and only runs in four-wheel drive when the system is manually engaged because more traction is desired. Two or four-wheel drive is normally selected by a lever to engage the front axle, but if locking hubs are used, these must also be manually engaged in the Lock position. Otherwise, the front axle will not drive the front wheels.
PASSIVE RESTRAINT: Safety systems such as air bags or automatic seat belts which operate with no action required on the part of the driver or passenger. Mandated by Federal regulations on all cars sold in the U.S. after 1990.
PAYLOAD: The weight the car is capable of carrying in addition to its own weight. Payload includes weight of the driver, passengers and cargo, but not coolant, fuel, lubricant, spare tire, etc.
PCM: Powertrain control module. See Electronic Control Unit (ECU).
PCV VALVE: A valve usually located in the rocker cover that vents crankcase vapors back into the engine to be reburned.
PERCOLATION: A condition in which the fuel actually "boils" due to excessive heat. Percolation prevents proper atomization of the fuel causing rough running.
PICK-UP COIL: The coil in which voltage is induced in an electronic ignition.
PING: A metallic rattling sound produced by the engine during acceleration. It is usually due to incorrect ignition timing or a poor grade of gasoline.
PINION: The smaller of two gears. The rear axle pinion drives the ring gear which transmits motion to the axle shafts.
PISTON RING: An open-ended ring which fits into a groove on the outer diameter of the piston. Its chief function is to form a seal between the piston and cylinder wall. Most automotive pistons have three rings: two for compression sealing; one for oil sealing.
PITMAN ARM: A lever which transmits steering force from the steering gear to the steering linkage.
Figure 22 Steering linkage  |
POLARITY: Indication (positive or negative) of the two poles of a battery.
POWER-TO-WEIGHT RATIO: Ratio of horsepower to weight of car.
POWERTRAIN: See Drivetrain.
Ppm: Parts per million; unit used to measure exhaust emissions.
PREIGNITION: Early ignition of fuel in the cylinder, sometimes due to glowing carbon deposits in the combustion chamber. Preignition can be damaging since combustion takes place prematurely.
PRELOAD: A predetermined load placed on a bearing during assembly or by adjustment.
PRESS FIT: The mating of two parts under pressure, due to the inner diameter of one being smaller than the outer diameter of the other, or vice versa; an interference fit.
PRESSURE PLATE: A spring-loaded plate (part of the clutch) that transmits power to the driven (friction) plate when the clutch is engaged.
PRIMARY CIRCUIT: The low voltage side of the ignition system which consists of the ignition switch, ballast resistor or resistance wire, bypass, coil, electronic control unit and pick-up coil as well as the connecting wires and harnesses.
PROFESSIONAL TECHNICIAN: A repair technician that has been properly trained in a vehicle’s systems. Usually affiliated with ASE or other certification system. This technician will also have the proper tools to diagnose and repair your vehicle.
PROFILE: Term used for tire measurement (tire series), which is the ratio of tire height to tread width.
Psi: Pounds per square inch; a measurement of pressure.
PUSHROD: A steel rod between the hydraulic valve lifter and the valve rocker arm in overhead valve (OHV) engines.
QUARTER PANEL: General term used to refer to a rear fender. Quarter panel is the area from the rear door opening to the tail light area and from rear wheelwell to the base of the trunk and roof-line.
RACE: The surface on the inner or outer ring of a bearing on which the balls, needles or rollers move.
RACK AND PINION: A type of automotive steering system using a pinion gear attached to the end of the steering shaft. The pinion meshes with a long rack attached to the steering linkage.
Figure 23 Rack and pinion steering  |
RADIATOR: Part of the cooling system for a water-cooled engine, mounted in the front of the car and connected to the engine with rubber hoses. Through the radiator, excess combustion heat is dissipated into the atmosphere through forced convection using a water and glycol based mixture that circulates through, and cools, the engine.
REAR MAIN OIL SEAL: A synthetic or rope-type seal that prevents oil from leaking out of the engine past the rear main crankshaft bearing.
RECALL: When a manufacturer recalls vehicles it has manufactured back to the dealership for specific repairs related to unplanned mechanical problems and/or safety issues. Recalls are usually voluntary and are made in conjunction with regulatory control of the National Highway Traffic Safety Agency (NHTSA). They can originate with the manufacturer or with the NHTSA. Repairs performed under a recall are usually free to the consumer.
RECIRCULATING BALL: Type of steering system in which recirculating steel balls occupy the area between the nut and worm wheel, causing a reduction in friction.
RECTIFIER: A device (used primarily in alternators) that permits electrical current to flow in one direction only.
REFRIGERANT 12 (R-12) or 134 (R-134): The generic name of the refrigerant used in automotive air conditioning systems.
REGULATOR: A device which maintains the amperage and/or voltage levels of a circuit at predetermined values.
RELAY: A switch which automatically opens and/or closes a circuit.
RELUCTOR: A wheel that rotates inside the distributor and triggers the release of voltage in an electronic ignition.
RESIN: A liquid plastic used in body work.
RESISTANCE: The opposition to the flow of current through a circuit or electrical device, and is measured in ohms. Resistance is equal to the voltage divided by the amperage.
RESISTOR SPARK PLUG: A spark plug using a resistor to shorten the spark duration. This suppresses radio interference and lengthens plug life.
RESISTOR: A device, usually made of wire, which offers a preset amount of resistance in an electrical circuit.
RETARD: Setting the ignition timing so that spark occurs later (fewer degrees before TDC).
RING GEAR: The name given to a ring-shaped gear attached to a differential case, or affixed to a flywheel or as part of a planetary gear set.
ROCKER ARM: A lever which rotates around a shaft pushing down (opening) the valve with an end when the other end is pushed up by the pushrod. Spring pressure will later close the valve.
Figure 24 Typical rocker arm and shaft assembly  |
ROLLER BEARING: A bearing made up of hardened inner and outer races between which hardened steel rollers move.
ROTOR: (1.) The disc-shaped part of a disc brake assembly, upon which the brake pads bear; also called brake disc. (2.) The device mounted atop the distributor shaft, which passes current to the distributor cap tower contacts.
Figure 25 Rotor mounted on top of distributor shaft  |
RPM: Revolutions per minute (usually indicates engine speed).
RUN-ON: Condition when the engine continues to run, even when the key is turned off. See dieseling.
SEALED BEAM: An automotive headlight. The lens, reflector and filament form a single unit.
SEATBELT INTERLOCK: A system whereby the car cannot be started unless the seatbelt is buckled.
SECONDARY CIRCUIT: The high voltage side of the ignition system, usually above 20,000 volts. The secondary includes the ignition coil, coil wire, distributor cap and rotor, spark plug wires and spark plugs.
SEMI-FLOATING AXLE: In this design, a wheel is attached to the axle shaft, which takes both drive and cornering loads. Almost all solid axle passenger cars and light trucks use this design.
SENDING UNIT: A mechanical, electrical, hydraulic or electromagnetic device which transmits information to a gauge.
SENSOR: Any device designed to measure engine operating conditions or ambient pressures and temperatures. Usually electronic in nature and designed to send a voltage signal to an on-board computer, some sensors may operate as a simple on/off switch or they may provide a variable voltage signal (like a potentiometer) as conditions or measured parameters change.
SERPENTINE BELT: An accessory drive belt, with small multiple v-ribs, routed around most or all of the engine-powered accessories such as the alternator and power steering pump. Usually both the front and the back side of the belt come into contact with various pulleys.
SHEATH: The outer casing for clutch or brake cables.
SHIM: Spacers of precise, predetermined thickness used between parts to establish a proper working relationship.
SHIMMY: Vibration (sometimes violent) in the front end caused by misaligned front end, out of balance tires or worn suspension components.
SHORT CIRCUIT: An electrical malfunction where current takes the path of least resistance to ground (usually through damaged insulation). Current flow is excessive from low resistance resulting in a blown fuse.
SINGLE OVERHEAD CAMSHAFT: See overhead camshaft.
SKIDPLATE: A metal plate attached to the underside of the body to protect the fuel tank, transfer case or other vulnerable parts from damage.
SLAVE CYLINDER: In automotive use, a device in the hydraulic clutch system which is activated by hydraulic force, disengaging the clutch.
SLUDGE: Thick, black deposits in engine formed from dirt, oil, water, etc. It is usually formed in engines when oil changes are neglected.
SNAP RING: A circular retaining clip used inside or outside a shaft or part to secure a shaft, such as a floating wrist pin.
SOHC: Single overhead camshaft.
SOLENOID: An electrically operated, magnetic switching device.
SPARK PLUG: A device screwed into the combustion chamber of a spark ignition engine. The basic construction is a conductive core inside of a ceramic insulator, mounted in an outer conductive base. An electrical charge from the spark plug wire travels along the conductive core and jumps a preset air gap to a grounding point or points at the end of the conductive base. The resultant spark ignites the fuel/air mixture in the combustion chamber.
SPECIFIC GRAVITY (BATTERY): The relative weight of liquid (battery electrolyte) as compared to the weight of an equal volume of water.
SPLINES: Ridges machined or cast onto the outer diameter of a shaft or inner diameter of a bore to enable parts to mate without rotation.
SPONGY PEDAL: A soft or spongy feeling when the brake pedal is depressed. It is usually due to air in the brake lines.
SPRUNG WEIGHT: The weight of a car supported by the springs.
SRS: Supplemental restraint system
STABILIZER (SWAY) BAR: A bar linking both sides of the suspension. It resists sway on turns by taking some of the added load from one wheel and putting it on the other.
STARTER: A high-torque electric motor used for the purpose of starting the engine, typically through a high ratio geared drive connected to the flywheel ring gear.
Figure 26 Starter motor assembly location  |
STRAIGHT WEIGHT: Term designating motor oil as suitable for use within a narrow range of temperatures. Outside the narrow temperature range, its flow characteristics will not adequately lubricate.
STROKE: The distance the piston travels from bottom dead center to top dead center.
SUPERCHARGER: An air pump driven mechanically by the engine through belts, chains, shafts or gears from the crankshaft. Two general types of supercharger are the positive displacement and centrifugal types, which pump air in direct relationship to the speed of the engine.
SUPPLEMENTAL RESTRAINT SYSTEM: See air bag.
SYNCHROMESH: A manual transmission that is equipped with devices (synchronizers) that match the gear speeds so that the transmission can be downshifted without clashing gears.
SYNTHETIC OIL: Non-petroleum based oil.
TAMPERING: Used in conjunction with a vehicles emission control system. Tampering is used to describe any alterations to the original design of the vehicles emission control system.
TAMPERING INSPECTION: An inspection done by State or Local authorities to determine if a vehicle's emission control system has been tampered with.
TACHOMETER: A device used to measure the rotary speed of an engine, shaft, gear, etc., usually in rotations per minute.
TDC: Top dead center. The exact top of the piston's stroke.
THERMOSTAT: A valve, located in the cooling system of an engine, which is closed when cold and opens gradually in response to engine heating, controlling the temperature of the coolant and rate of coolant flow.
THROW-OUT BEARING: As the clutch pedal is depressed, the throwout bearing moves against the spring fingers of the pressure plate, forcing the pressure plate to disengage from the driven disc.
TIE ROD: A rod connecting the steering arms. Tie rods have threaded ends that are used to adjust toe-in.
TIMING BELT: A square-toothed, reinforced rubber belt that is driven by the crankshaft and operates the camshaft.
TIMING CHAIN: A roller chain that is driven by the crankshaft and operates the camshaft.
TIRE ROTATION: Moving the tires from one position to another to make the tires wear evenly.
TOE-IN (OUT): A term comparing the extreme front and rear of the front tires. Closer together at the front is toe-in; farther apart at the front is toe-out.
Figure 27 Wheel toe-in (top view)  |
TORQUE: Measurement of turning or twisting force, expressed as foot-pounds or inch-pounds.
TORQUE CONVERTER: A turbine used to transmit power from a driving member to a driven member via hydraulic action, providing changes in drive ratio and torque. In automotive use, it links the driveplate at the rear of the engine to the automatic transmission.
TORSION BAR SUSPENSION: Long rods of spring steel which take the place of springs. One end of the bar is anchored and the other arm (attached to the suspension) is free to twist. The bars' resistance to twisting causes springing action.
Figure 28 Torsion bar front suspension  |
TRACTION CONTROL: A control system that prevents the spinning of a car's drive wheels when excess power is applied.
TRANSAXLE: A single housing containing the transmission and differential. Transaxles are usually found on front engine/front wheel drive or rear engine/rear wheel drive cars.
TRANSDUCER: A device used to change a force into an electrical signal.
TRANSFER CASE: A gearbox driven from the transmission that delivers power to both front and rear driveshafts in a four-wheel drive system. Transfer cases usually have a high and low range set of gears, used depending on how much pulling power is needed.
TRANSISTOR: A semi-conductor component which can be actuated by a small voltage to perform an electrical switching function.
TREAD WEAR INDICATOR: Bars molded into the tire at right angles to the tread that appear as horizontal bars when
Figure 29 Location of tire tread wear indicators  |
TSB: Acronym for Technical Service Bulletin. This bulletin is produced by the vehicle manufacturer and alerts automotive technicians about specific service problem areas, repair procedures, and new service techniques for a vehicle.
TUNE-UP: A regular maintenance function, usually associated with the replacement and adjustment of parts and components in the electrical and fuel systems of a car for the purpose of attaining optimum performance.
TURBOCHARGER: An exhaust driven pump which compresses intake air and forces it into the combustion chambers at higher than atmospheric pressures. The increased air pressure allows more fuel to be burned and results in increased horsepower being produced.
Figure 30 The turbocharged engine principle uses exhaust gas to spin the turbocharger, increasing maximum engine power output  |
U-JOINT (UNIVERSAL JOINT): A flexible coupling in the drive train that allows the driveshafts or axle shafts to operate at different angles and still transmit rotary power.
ULTRAVIOLET LIGHT: A light used in conjunction with a fluorescent dye to detect leaks in the engine, transmission or cooling system.
UNDER LOAD: Used to describe the condition of a vehicle when climbing a steep incline or hill. When the vehicle is placed under a higher than normal amount of load when carrying excessive cargo.
UNDERSTEER: The tendency of a car to continue straight ahead while negotiating a turn.
UNIT BODY: Design in which the car body acts as the frame.
UNLEADED FUEL: Fuel which contains no lead (a common gasoline additive). The presence of lead in fuel will destroy the functioning elements of a catalytic converter, making it useless.
UNSPRUNG WEIGHT: The weight of car components not supported by the springs (wheels, tires, brakes, rear axle, control arms, etc.).
VACUUM ADVANCE: A device which advances the ignition timing in response to increased engine vacuum.
VACUUM MODULATOR: A device used to control the transmission shift points based on the amount of load placed on the engine.
VACUUM GAUGE: An instrument used to measure the presence of vacuum in a chamber.
VALVE: A device which control the pressure, direction of flow or rate of flow of a liquid or gas.
VALVE CLEARANCE: The measured gap between the end of the valve stem and the rocker arm, cam lobe or follower that activates the valve.
VALVE GUIDES: The guide through which the stem of the valve passes. The guide is designed to keep the valve in proper alignment.
VALVE LASH (CLEARANCE): The operating clearance in the valve train.
VALVE STEM SEALS: Synthetic rubber seals that are used to control the oil that lubricates the valve stems in the valve guides. Worn valve stem seals can cause blue smoke from the exhaust when first starting the engine.
VALVE TRAIN: The system that operates intake and exhaust valves, consisting of camshaft, valves and springs, lifters, pushrods and rocker arms.
VAPOR LOCK: Boiling of the fuel in the fuel lines due to excess heat. This will interfere with the flow of fuel in the lines and can completely stop the flow. Vapor lock normally only occurs in hot weather.
VARNISH: Term applied to the residue formed when gasoline gets old and stale.
VCM: See Electronic Control Unit (ECU).
VISCOSITY: The ability of a fluid to flow. The lower the viscosity rating, the easier the fluid will flow. 10 weight motor oil will flow much easier than 40 weight motor oil.
VOLT: Unit used to measure the force or pressure of electricity. It is defined as the pressure needed to move one amp through a resistance of one ohm.
VOLTAGE REGULATOR: A device that controls the current output of the alternator or generator.
VOLTMETER: An instrument used for measuring electrical force in units called volts. Voltmeters are always connected parallel with the circuit being tested.
WANKEL ENGINE: An engine which uses no pistons. In place of pistons, triangular-shaped rotors revolve in specially shaped housings.
WATER PUMP: A belt driven component of the cooling system that mounts on the engine, circulating the coolant under pressure.
WEAR INDICATORS: A metal tab mounted on disc brake pads that touch the brake rotor when the brake linings need replacement.
Figure 31 Water pump mounting onto front of the engine block  |
WHEEL CYLINDER: Found in the automotive drum brake assembly, it is a device, actuated by hydraulic pressure, which, through internal pistons, pushes the brake shoes outward against the drums.
Figure 32 Drum brake components  |
WHEELBASE: Distance between the center of front wheels and the center of rear wheels.
Glossary of automotive 1
EAD CENTER: The extreme top or bottom of the piston stroke.
DETERGENT: An additive in engine oil to improve its operating characteristics.
DETONATION: An unwanted explosion of the air/fuel mixture in the combustion chamber caused by excess heat and compression, advanced timing, or an overly lean mixture. Also referred to as "ping".
DEXRON: A brand of automatic transmission fluid.
DIAPHRAGM: A thin flexible wall separating two cavities, such as in a vacuum advance unit.
DIESELING: The engine continues to run after the car is shut off; caused by fuel continuing to be burned in the combustion chamber.
DIFFERENTIAL: A geared assembly which allows the transmission of motion between drive axles, giving one axle the ability to rotate faster than the other, as in cornering.
DIGITAL VOLT OHMMETER: An electronic diagnostic tool used to measure voltage, ohms and amps as well as several other functions, with the readings displayed on a digital screen in tenths, hundredths and thousandths.
DIODE: An electrical device that will allow current to flow in one direction only.
DIRECT CURRENT (DC): Electrical current that flows in one direction only.
DISC BRAKE: A hydraulic braking assembly consisting of a brake disc, or rotor, mounted on an axleshaft, and a caliper assembly containing usually two brake pads which are activated by hydraulic pressure. The pads are forced against the sides of the disc, creating friction which slows the car.
DISPLACEMENT: The total volume of air that is displaced by all pistons as the engine turns through one complete revolution.
DISTRIBUTOR: A mechanically driven device on an engine which is responsible for electrically firing the spark plug at a pre-determined point of the piston stroke.
DOHC: Double overhead camshaft.
DOUBLE OVERHEAD CAMSHAFT: The engine utilizes two camshafts mounted in one cylinder head. One camshaft operates the exhaust valves, while the other operates the intake valves.
DOWEL PIN: A pin, inserted in mating holes in two different parts, allowing those parts to maintain a fixed relationship.
DRIVE CYCLE TEST: A function of the vehicle on board computer that includes the testing of the monitored systems that requires a start up -- from a cold engine to a warm engine -- and the vehicle being driven.
DRIVE TRAIN: The components that transmit the flow of power from the engine to the wheels. The components include the clutch, transmission, driveshafts (or axle shafts in front wheel drive), U-joints and differential.
DRUM BRAKE: A braking system which consists of two brake shoes and one or two wheel cylinders, mounted on a fixed backing plate, and a brake drum, mounted on an axle, which revolves around the assembly.
DRY CHARGED BATTERY: Battery to which electrolyte is added when the battery is placed in service.
DVOM: Digital volt ohmmeter
DWELL: The rate, measured in degrees of shaft rotation, at which an electrical circuit cycles on and off.
DYNAMOMETER: Various devices used in testing a motor or engine for such characteristics as efficiency and torque, especially an instrument that measures current or the power of a motor by calculating the force between a fixed coil and a moving coil.
EBCM: See Electronic Control Unit (ECU).
ECM: See Electronic Control Unit (ECU).
ENGINE CONTROL SYSTEM: The computer control system that regulates fuel delivery, ignition timing, engine idle speed and on some vehicles the transmission shift points.
ECU: Electronic control unit.
ELECTRODE: Conductor (positive or negative) of electric current.
ELECTROLYTE: A solution of water and sulfuric acid used to activate the battery. Electrolyte is extremely corrosive.
ELECTRONIC ACTUATION SYSTEM: The electronic controls for an anti-lock braking system or electronic suspension system. This unit contains the control computer for the individual system.
ELECTRONIC CONTROL UNIT: A digital computer that controls engine (and sometimes transmission, brake or other car system) functions based on data received from various sensors. Examples used by some manufacturers include Electronic Brake Control Module (EBCM), Engine Control Module (ECM), Powertrain Control Module (PCM) or Vehicle Control Module (VCM).
ELECTRONIC IGNITION: A system in which the timing and firing of the spark plugs is controlled by an electronic control unit, usually called a module. These systems have no points or condenser.
ENAMEL: Type of paint that dries to a smooth, glossy finish.
END-PLAY: The measured amount of axial movement in a shaft.
ENGINE: The primary motor or power apparatus of a car, which converts liquid or gas fuel into mechanical energy.
ENGINE BLOCK: The basic engine casting containing the cylinders, the crankshaft main bearings, as well as machined surfaces for the mounting of other components such as the cylinder head, oil pan, transmission, etc..
EP LUBRICANT: EP (extreme pressure) lubricants are specially formulated for use with gears involving heavy loads (transmissions, differentials, etc.).
ETHYL: A substance added to gasoline to improve its resistance to knock, by slowing down the rate of combustion.
ETHYLENE GLYCOL: The base substance of antifreeze.
EXHAUST MANIFOLD: A set of cast passages or pipes which conduct exhaust gases from the engine.
FAST IDLE: The speed of the engine when the choke is on. Fast idle speeds engine warm-up.
FEDERAL ENGINE: An engine certified by the EPA for use in any of the 49 states (except California).
FEELER GAUGE: A blade, usually metal, of precisely predetermined thickness, used to measure the clearance between two parts.
FILAMENT: The part of a bulb that glows; the filament creates high resistance to current flow and actually glows from the resulting heat.
FINAL DRIVE: See axle ratio.
FIRING ORDER: The order in which combustion occurs in the cylinders of an engine. Also the order in which spark is distributed to the plugs by the distributor.
FLAME FRONT: The term used to describe certain aspects of the fuel combustion in the cylinders. The flame front should move in a controlled pattern across the cylinder, rather than simply combusting immediately.
FLAT ENGINE: Engine design in which the pistons are horizontally opposed. Porsche, Subaru and some old VWs are common examples of flat engines.
FLAT RATE: A dealership term referring to the standard fee charged by a technician for a particular repair or diagnostic service versus the actual labor time.
FLAT SPOT: A point during acceleration when the engine seems to lose power for an instant.
FLOODING: The presence of too much fuel in the intake manifold and combustion chamber which prevents the air/fuel mixture from firing, thereby causing a no-start situation.
FLYWHEEL: A heavy disc of metal attached to the rear of the crankshaft. It smoothes the firing impulses of the engine and keeps the crankshaft turning during periods when no firing takes place. The starter also engages the flywheel to start the engine.
FOOT POUND (ft. lbs. or sometimes ft. lb.): The amount of energy or work needed to raise an item weighing one pound a distance of one foot.
FREEPLAY: The amount of travel in a clutch pedal or brake pedal before movement of the clutch or brakes take place. This adjustment is critical to the proper operation of the clutch or brakes.
FREEZE PLUG: A plug in the engine block which will be pushed out if the coolant freezes. Sometimes called expansion plugs, they protect the block from cracking should the coolant freeze.
FRONT END ALIGNMENT: A service to set caster, camber and toe-in to the correct specifications. This will ensure that the car steers and handles properly and that the tires wear properly.
FRONTAL AREA: The total surface area of the front of a car that is exposed to air flow.
FUEL FILTER: A component of the fuel system containing a porous paper element used to prevent any impurities from entering the engine through the fuel system. It usually takes the form of a canister-like housing, mounted in-line with the fuel hose, located anywhere on a car between the fuel tank and engine.
FUEL INJECTION: A system replacing the carburetor that sprays fuel into the cylinder through nozzles. The amount of fuel can be more precisely controlled with fuel injection.
FULL FLOATING AXLE: An axle in which the axle housing extends through the wheel giving bearing support on the outside of the housing. The front axle of a four-wheel drive car is usually a full floating axle, as are the rear axles of many larger (3/4 ton and over) pick-ups and vans.
FULL-TIME FOUR-WHEEL DRIVE: A four-wheel drive system that continuously delivers power to all four wheels. A differential between the front and rear driveshafts permits variations in axle speeds to control gear wind-up without damage.
FUSE: A protective device in a circuit which prevents circuit overload by breaking the circuit when a specific amperage is present. The device is constructed around a strip or wire of a lower amperage rating than the circuit it is designed to protect. When an amperage higher than that stamped on the fuse is present in the circuit, the strip or wire melts, opening the circuit.
FUSIBLE LINK: A piece of wire in a wiring harness that performs the same service as a fuse. If overloaded, the fusible link will melt and interrupt the circuit.
FWD: Front wheel drive.
GAS ANALYZER: A tool used to test the exhaust emissions of a vehicle. Gases tested include CO (carbon monoxide), CO2 (carbon dioxide), HC (hydrocarbons), O2 (oxygen) and sometimes NOx (oxides of nitrogen).
GAWR: Gross axle weight rating. The total maximum weight an axle is designed to carry.
GCW: Gross combined weight. The total combined weight of a tow car and trailer.
GEAR RATIO: A ratio expressing the number of turns a smaller gear will make to turn a larger gear through one revolution. The ratio is found by dividing the number of teeth on the smaller gear into the number of teeth on the larger gear.
GEARBOX: Transmission
GEL COAT: A thin coat of plastic resin covering fiberglass body panels.
GENERATOR: A device which produces direct current (DC) necessary to charge the battery.
GVWR: Gross vehicle weight rating. The total maximum weight a car is designed to carry including the weight of the car, passengers, equipment, gas, oil, etc.
HALOGEN: A special type of lamp known for its quality of brilliant white light. Originally used for fog lights and driving lights.
HEADER TANK: An expansion tank for the radiator coolant. It can be located remotely or built into the radiator.
HEAT RANGE: A term used to describe the ability of a spark plug to carry away heat. Plugs with longer nosed insulators take longer to carry heat off effectively.
HEAT RISER: A flapper in the exhaust manifold that is closed when the engine is cold, causing hot exhaust gases to heat the intake manifold providing better cold engine operation. A thermostatic spring opens the flapper when the engine warms up.
HEATER CONTROL VALVE: The device that controls the flow of hot engine coolant through the heater core.
HEMI: A name given an engine using hemispherical combustion chambers.
HORSEPOWER: A measurement of the amount of work; one horsepower is the amount of work necessary to lift 33,000 lbs. one foot in one minute. Brake horsepower (bhp) is the horsepower delivered by an engine on a dynamometer. Net horsepower is the power remaining (measured at the flywheel of the engine) that can be used to turn the wheels after power is consumed through friction and running the engine accessories (water pump, alternator, air pump, fan etc.)
HUB: The center part of a wheel or gear.
HYDROCARBON (HC): Any chemical compound made up of hydrogen and carbon. A major pollutant formed by the engine as a by-product of combustion.
HYDROMETER: An instrument used to measure the specific gravity of a solution.
HYDROPLANING: A phenomenon of driving when water builds up under the tire tread, causing it to lose contact with the road. Slowing down will usually restore normal tire contact with the road.
HVAC: Heating, ventilation and air conditioning system.
IDLE MIXTURE: The mixture of air and fuel (usually about 14:1) being fed to the cylinders. The idle mixture screw(s) are sometimes adjusted as part of a tune-up.
IDLER ARM: Component of the steering linkage which is a geometric duplicate of the steering gear arm. It supports the right side of the center steering link.
INCH POUND (inch lbs. or sometimes in. lb. or in. lbs.): One twelfth of a foot pound.
INDUCTION: A means of transferring electrical energy in the form of a magnetic field. Principle used in the ignition coil to increase voltage.
INJECTOR: A device which receives metered fuel under relatively low pressure and is activated to inject the fuel into the engine under relatively high pressure at a predetermined time.
INPUT SHAFT: The shaft to which torque is applied, usually carrying the driving gear or gears.
INTAKE MANIFOLD: A casting of passages or pipes used to conduct air or a fuel/air mixture to the cylinders.
JOURNAL: The bearing surface within which a shaft operates.
JUMPER CABLES: Two heavy duty wires with large alligator clips used to provide power from a charged battery to a discharged battery mounted in a car.
JUMPSTART: Utilizing the sufficiently charged battery of one car to start the engine of another car with a discharged battery by the use of jumper cables.
KEY: A small block usually fitted in a notch between a shaft and a hub to prevent slippage of the two parts.
KNOCK: Noise which results from the spontaneous ignition of a portion of the air-fuel mixture in the engine cylinder caused by overly advanced ignition timing or use of incorrectly low octane fuel for that engine.
KNOCK SENSOR: An input device that responds to spark knock, caused by overly advanced ignition timing.
LABOR TIME: A specific amount of time required to perform a certain repair or diagnostic service as defined by a car or after-market manufacturer .
LACQUER: A quick-drying automotive paint.
LIMITED SLIP: A type of differential which transfers driving force to the wheel with the best traction.
LITHIUM-BASE GREASE: Chassis and wheel bearing grease using lithium as a base. Not compatible with sodium-base grease.
LOAD RANGE: Indicates the number of plies at which a tire is rated. Load range B equals four-ply rating; C equals six-ply rating; and, D equals an eight-ply rating.
LOCKING HUBS: Accessories used on part-time four-wheel drive systems that allow the front wheels to be disengaged from the drive train when four-wheel drive is not being used. When four-wheel drive is desired, the hubs are engaged, locking the wheels to the drive train.
LOCK RING: See Circlip or Snapring
MANIFOLD: A casting of passages or set of pipes which connect the cylinders to an inlet or outlet source.
MANIFOLD VACUUM: Low pressure in an engine intake manifold formed just below the throttle plates. Manifold vacuum is highest at idle and drops under acceleration.
MASTER CYLINDER: The primary fluid pressurizing device in a hydraulic system. In automotive use, it is found in brake and hydraulic clutch systems and is pedal activated, either directly or, in a power brake system, through the power booster.
McPHERSON STRUT: A suspension component combining a shock absorber and spring in one unit.
MISFIRE: Condition occurring when the fuel mixture in a cylinder fails to ignite, causing the engine to run roughly.
MODULE: Electronic control unit, amplifier or igniter of solid state or integrated design which controls the current flow in the ignition primary circuit based on input from the pick-up coil. When the module opens the primary circuit, high secondary voltage is induced in the coil.
MULTI-WEIGHT: Type of oil that provides adequate lubrication at both high and low temperatures
NEEDLE BEARING: A bearing which consists of a number (usually a large number) of long, thin rollers.
NITROGEN OXIDE (NOx): One of the three basic pollutants found in the exhaust emission of an internal combustion engine. The amount of NOx usually varies in an inverse proportion to the amount of HC and CO.
DETERGENT: An additive in engine oil to improve its operating characteristics.
DETONATION: An unwanted explosion of the air/fuel mixture in the combustion chamber caused by excess heat and compression, advanced timing, or an overly lean mixture. Also referred to as "ping".
DEXRON: A brand of automatic transmission fluid.
DIAPHRAGM: A thin flexible wall separating two cavities, such as in a vacuum advance unit.
DIESELING: The engine continues to run after the car is shut off; caused by fuel continuing to be burned in the combustion chamber.
DIFFERENTIAL: A geared assembly which allows the transmission of motion between drive axles, giving one axle the ability to rotate faster than the other, as in cornering.
Figure 12 Differential action during cornering  |
DIODE: An electrical device that will allow current to flow in one direction only.
DIRECT CURRENT (DC): Electrical current that flows in one direction only.
DISC BRAKE: A hydraulic braking assembly consisting of a brake disc, or rotor, mounted on an axleshaft, and a caliper assembly containing usually two brake pads which are activated by hydraulic pressure. The pads are forced against the sides of the disc, creating friction which slows the car.
DISPLACEMENT: The total volume of air that is displaced by all pistons as the engine turns through one complete revolution.
DISTRIBUTOR: A mechanically driven device on an engine which is responsible for electrically firing the spark plug at a pre-determined point of the piston stroke.
Figure 13 Typical distributor assembly  |
DOUBLE OVERHEAD CAMSHAFT: The engine utilizes two camshafts mounted in one cylinder head. One camshaft operates the exhaust valves, while the other operates the intake valves.
DOWEL PIN: A pin, inserted in mating holes in two different parts, allowing those parts to maintain a fixed relationship.
DRIVE CYCLE TEST: A function of the vehicle on board computer that includes the testing of the monitored systems that requires a start up -- from a cold engine to a warm engine -- and the vehicle being driven.
DRIVE TRAIN: The components that transmit the flow of power from the engine to the wheels. The components include the clutch, transmission, driveshafts (or axle shafts in front wheel drive), U-joints and differential.
DRUM BRAKE: A braking system which consists of two brake shoes and one or two wheel cylinders, mounted on a fixed backing plate, and a brake drum, mounted on an axle, which revolves around the assembly.
DRY CHARGED BATTERY: Battery to which electrolyte is added when the battery is placed in service.
DVOM: Digital volt ohmmeter
Figure 14 Performing a resistance check using a DVOM  |
DYNAMOMETER: Various devices used in testing a motor or engine for such characteristics as efficiency and torque, especially an instrument that measures current or the power of a motor by calculating the force between a fixed coil and a moving coil.
EBCM: See Electronic Control Unit (ECU).
ECM: See Electronic Control Unit (ECU).
ENGINE CONTROL SYSTEM: The computer control system that regulates fuel delivery, ignition timing, engine idle speed and on some vehicles the transmission shift points.
ECU: Electronic control unit.
ELECTRODE: Conductor (positive or negative) of electric current.
ELECTROLYTE: A solution of water and sulfuric acid used to activate the battery. Electrolyte is extremely corrosive.
ELECTRONIC ACTUATION SYSTEM: The electronic controls for an anti-lock braking system or electronic suspension system. This unit contains the control computer for the individual system.
ELECTRONIC CONTROL UNIT: A digital computer that controls engine (and sometimes transmission, brake or other car system) functions based on data received from various sensors. Examples used by some manufacturers include Electronic Brake Control Module (EBCM), Engine Control Module (ECM), Powertrain Control Module (PCM) or Vehicle Control Module (VCM).
ELECTRONIC IGNITION: A system in which the timing and firing of the spark plugs is controlled by an electronic control unit, usually called a module. These systems have no points or condenser.
ENAMEL: Type of paint that dries to a smooth, glossy finish.
END-PLAY: The measured amount of axial movement in a shaft.
ENGINE: The primary motor or power apparatus of a car, which converts liquid or gas fuel into mechanical energy.
ENGINE BLOCK: The basic engine casting containing the cylinders, the crankshaft main bearings, as well as machined surfaces for the mounting of other components such as the cylinder head, oil pan, transmission, etc..
EP LUBRICANT: EP (extreme pressure) lubricants are specially formulated for use with gears involving heavy loads (transmissions, differentials, etc.).
ETHYL: A substance added to gasoline to improve its resistance to knock, by slowing down the rate of combustion.
ETHYLENE GLYCOL: The base substance of antifreeze.
EXHAUST MANIFOLD: A set of cast passages or pipes which conduct exhaust gases from the engine.
Figure 15 Typical exhaust manifold  |
FEDERAL ENGINE: An engine certified by the EPA for use in any of the 49 states (except California).
FEELER GAUGE: A blade, usually metal, of precisely predetermined thickness, used to measure the clearance between two parts.
FILAMENT: The part of a bulb that glows; the filament creates high resistance to current flow and actually glows from the resulting heat.
FINAL DRIVE: See axle ratio.
FIRING ORDER: The order in which combustion occurs in the cylinders of an engine. Also the order in which spark is distributed to the plugs by the distributor.
FLAME FRONT: The term used to describe certain aspects of the fuel combustion in the cylinders. The flame front should move in a controlled pattern across the cylinder, rather than simply combusting immediately.
FLAT ENGINE: Engine design in which the pistons are horizontally opposed. Porsche, Subaru and some old VWs are common examples of flat engines.
FLAT RATE: A dealership term referring to the standard fee charged by a technician for a particular repair or diagnostic service versus the actual labor time.
FLAT SPOT: A point during acceleration when the engine seems to lose power for an instant.
FLOODING: The presence of too much fuel in the intake manifold and combustion chamber which prevents the air/fuel mixture from firing, thereby causing a no-start situation.
FLYWHEEL: A heavy disc of metal attached to the rear of the crankshaft. It smoothes the firing impulses of the engine and keeps the crankshaft turning during periods when no firing takes place. The starter also engages the flywheel to start the engine.
Figure 16 The flywheel is mounted to the rear of the crankshaft  |
FREEPLAY: The amount of travel in a clutch pedal or brake pedal before movement of the clutch or brakes take place. This adjustment is critical to the proper operation of the clutch or brakes.
FREEZE PLUG: A plug in the engine block which will be pushed out if the coolant freezes. Sometimes called expansion plugs, they protect the block from cracking should the coolant freeze.
FRONT END ALIGNMENT: A service to set caster, camber and toe-in to the correct specifications. This will ensure that the car steers and handles properly and that the tires wear properly.
FRONTAL AREA: The total surface area of the front of a car that is exposed to air flow.
FUEL FILTER: A component of the fuel system containing a porous paper element used to prevent any impurities from entering the engine through the fuel system. It usually takes the form of a canister-like housing, mounted in-line with the fuel hose, located anywhere on a car between the fuel tank and engine.
Figure 17 The fuel filter is mounted in-line with the fuel hose  |
FULL FLOATING AXLE: An axle in which the axle housing extends through the wheel giving bearing support on the outside of the housing. The front axle of a four-wheel drive car is usually a full floating axle, as are the rear axles of many larger (3/4 ton and over) pick-ups and vans.
FULL-TIME FOUR-WHEEL DRIVE: A four-wheel drive system that continuously delivers power to all four wheels. A differential between the front and rear driveshafts permits variations in axle speeds to control gear wind-up without damage.
FUSE: A protective device in a circuit which prevents circuit overload by breaking the circuit when a specific amperage is present. The device is constructed around a strip or wire of a lower amperage rating than the circuit it is designed to protect. When an amperage higher than that stamped on the fuse is present in the circuit, the strip or wire melts, opening the circuit.
FUSIBLE LINK: A piece of wire in a wiring harness that performs the same service as a fuse. If overloaded, the fusible link will melt and interrupt the circuit.
FWD: Front wheel drive.
GAS ANALYZER: A tool used to test the exhaust emissions of a vehicle. Gases tested include CO (carbon monoxide), CO2 (carbon dioxide), HC (hydrocarbons), O2 (oxygen) and sometimes NOx (oxides of nitrogen).
GAWR: Gross axle weight rating. The total maximum weight an axle is designed to carry.
GCW: Gross combined weight. The total combined weight of a tow car and trailer.
GEAR RATIO: A ratio expressing the number of turns a smaller gear will make to turn a larger gear through one revolution. The ratio is found by dividing the number of teeth on the smaller gear into the number of teeth on the larger gear.
GEARBOX: Transmission
GEL COAT: A thin coat of plastic resin covering fiberglass body panels.
GENERATOR: A device which produces direct current (DC) necessary to charge the battery.
GVWR: Gross vehicle weight rating. The total maximum weight a car is designed to carry including the weight of the car, passengers, equipment, gas, oil, etc.
HALOGEN: A special type of lamp known for its quality of brilliant white light. Originally used for fog lights and driving lights.
HEADER TANK: An expansion tank for the radiator coolant. It can be located remotely or built into the radiator.
HEAT RANGE: A term used to describe the ability of a spark plug to carry away heat. Plugs with longer nosed insulators take longer to carry heat off effectively.
HEAT RISER: A flapper in the exhaust manifold that is closed when the engine is cold, causing hot exhaust gases to heat the intake manifold providing better cold engine operation. A thermostatic spring opens the flapper when the engine warms up.
HEATER CONTROL VALVE: The device that controls the flow of hot engine coolant through the heater core.
HEMI: A name given an engine using hemispherical combustion chambers.
HORSEPOWER: A measurement of the amount of work; one horsepower is the amount of work necessary to lift 33,000 lbs. one foot in one minute. Brake horsepower (bhp) is the horsepower delivered by an engine on a dynamometer. Net horsepower is the power remaining (measured at the flywheel of the engine) that can be used to turn the wheels after power is consumed through friction and running the engine accessories (water pump, alternator, air pump, fan etc.)
HUB: The center part of a wheel or gear.
HYDROCARBON (HC): Any chemical compound made up of hydrogen and carbon. A major pollutant formed by the engine as a by-product of combustion.
HYDROMETER: An instrument used to measure the specific gravity of a solution.
HYDROPLANING: A phenomenon of driving when water builds up under the tire tread, causing it to lose contact with the road. Slowing down will usually restore normal tire contact with the road.
HVAC: Heating, ventilation and air conditioning system.
IDLE MIXTURE: The mixture of air and fuel (usually about 14:1) being fed to the cylinders. The idle mixture screw(s) are sometimes adjusted as part of a tune-up.
IDLER ARM: Component of the steering linkage which is a geometric duplicate of the steering gear arm. It supports the right side of the center steering link.
INCH POUND (inch lbs. or sometimes in. lb. or in. lbs.): One twelfth of a foot pound.
INDUCTION: A means of transferring electrical energy in the form of a magnetic field. Principle used in the ignition coil to increase voltage.
INJECTOR: A device which receives metered fuel under relatively low pressure and is activated to inject the fuel into the engine under relatively high pressure at a predetermined time.
INPUT SHAFT: The shaft to which torque is applied, usually carrying the driving gear or gears.
INTAKE MANIFOLD: A casting of passages or pipes used to conduct air or a fuel/air mixture to the cylinders.
Figure 18 Typical intake manifold for a 4-cylinder engine  |
JUMPER CABLES: Two heavy duty wires with large alligator clips used to provide power from a charged battery to a discharged battery mounted in a car.
JUMPSTART: Utilizing the sufficiently charged battery of one car to start the engine of another car with a discharged battery by the use of jumper cables.
KEY: A small block usually fitted in a notch between a shaft and a hub to prevent slippage of the two parts.
KNOCK: Noise which results from the spontaneous ignition of a portion of the air-fuel mixture in the engine cylinder caused by overly advanced ignition timing or use of incorrectly low octane fuel for that engine.
KNOCK SENSOR: An input device that responds to spark knock, caused by overly advanced ignition timing.
LABOR TIME: A specific amount of time required to perform a certain repair or diagnostic service as defined by a car or after-market manufacturer .
LACQUER: A quick-drying automotive paint.
LIMITED SLIP: A type of differential which transfers driving force to the wheel with the best traction.
LITHIUM-BASE GREASE: Chassis and wheel bearing grease using lithium as a base. Not compatible with sodium-base grease.
LOAD RANGE: Indicates the number of plies at which a tire is rated. Load range B equals four-ply rating; C equals six-ply rating; and, D equals an eight-ply rating.
LOCKING HUBS: Accessories used on part-time four-wheel drive systems that allow the front wheels to be disengaged from the drive train when four-wheel drive is not being used. When four-wheel drive is desired, the hubs are engaged, locking the wheels to the drive train.
LOCK RING: See Circlip or Snapring
MANIFOLD: A casting of passages or set of pipes which connect the cylinders to an inlet or outlet source.
MANIFOLD VACUUM: Low pressure in an engine intake manifold formed just below the throttle plates. Manifold vacuum is highest at idle and drops under acceleration.
MASTER CYLINDER: The primary fluid pressurizing device in a hydraulic system. In automotive use, it is found in brake and hydraulic clutch systems and is pedal activated, either directly or, in a power brake system, through the power booster.
Figure 19 Master cylinder  |
Figure 20 McPherson struts combine shocks and springs in one assembly  |
MODULE: Electronic control unit, amplifier or igniter of solid state or integrated design which controls the current flow in the ignition primary circuit based on input from the pick-up coil. When the module opens the primary circuit, high secondary voltage is induced in the coil.
MULTI-WEIGHT: Type of oil that provides adequate lubrication at both high and low temperatures
NEEDLE BEARING: A bearing which consists of a number (usually a large number) of long, thin rollers.
NITROGEN OXIDE (NOx): One of the three basic pollutants found in the exhaust emission of an internal combustion engine. The amount of NOx usually varies in an inverse proportion to the amount of HC and CO.
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