Engine, Body Sensor, and Relay Glossary

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A

A-Pillar  - The roof support on either side of a vehicle's windshield. A-pillars are designed to support a large portion of the vehicle's weight in the event of a roll-over.

ABDC - After Bottom Dead Center

A/C Cutout Relay - The Air Conditioning Cutout Relay is connected in series with the air conditioner damped pressure switch, the air conditioner switch, and the radiator/condensor fan relay(2.5L engines) .  Information is sent to the sensor from the computer to engage and disengage the compressor clutch.  The clutch is deenergized at wide open throttle(WOT) or at a very low idle.

A/C Damped Pressure Switch - A pressure activated switch that controls the air-conditioner-compressor clutch action to prevent evaporator icing.

A/C Fan RelayThe A/C fan relay controls the cooling fan for the condensor when the A/C system is on. On a 2 speed fan system the A/C fan relay normally controls the high speed of the cooling fan.  The relay is normally open and is closed when the A/C system is turned on.

Adaptive Memory - The feature of a computer memory that allows the microprocessor to automatically compensate for changes in the dynamics of the process being controlled. Anything stored in adaptive memory is lost when power to the computer is interrupted, such as when the battery is disconnected.

Additive - A substance added in small amounts to something. The most common types of automotive additives are fuel additives (such as fuel injector cleaner) and oil additives (such as friction modifiers). MotorUP®, DuraLube®, Slick-50®, and Prolong® are examples of popular friction modifiers added to motor oil.

A/F - an abbreviation for Air to Fuel ratio

Air Bag -

Air Dam - A spoiler mounted beneath the front bumper of a vehicle and designed to alter the flow of air under the vehicle. Air dams are often used to increase the airflow to a radiator, decrease lift, and reduce aerodynamic drag.

Air/Fuel Ratio - The Air/Fuel Ratio is the ratio of air to gasoline by weight in the fuel mixture drawn in by the engine.

AIS(Automatic Idle Speed) - The Automatic Idle Speed Motor(AIS) is operated by the computer.  The computer takes readings from various sensors and adjust the engine idle to an optimum during all idling conditions.

Alloy - A metal containing additions of other metallic or nonmetallic elements to enhance specific properties such as strength and corrosion resistance.

Alternator - A device used for converting mechanical energy into electrical energy

American Wire Gauge  (AWG) - A system of measuring the size of wire. The smaller the wire the larger the gauge. For Example: 1-4 gauge wire is very thick and commonly used for high-current battery cables, while 14-18 gauge wire is very thin and commonly used for low-current wiring harnesses.

Angle of Approach - When viewed from the side; the line from the bottom of the front tire to the lowest-hanging component in front of the tire. This angle is an approximate indication of how steep an incline a vehicle can approach without damaging the front of the vehicle.

Angle of Departure - When viewed from the side; the line from the bottom of the rear tire to the lowest-hanging component behind the tire. This angle is an approximate indication of how steep an incline a vehicle can descend without damaging the rear of the vehicle.

Antidive - A suspension characteristic in which the downward force on the front of a vehicle, caused by the transfer of a vehicle's weight when braking, is resisted.

Antiroll Bar/Sway Bar - A suspension component (used at the front and/or the rear) that reduces body roll by resisting any unequal vertical motion between the pair of wheels to which it is connected. An antiroll bar does not affect suspension stiffness when both wheels are deflected equally in the same direction. Antiroll bars are often referred to as Sway Bars or Stabalizer Bars.

Antisquat - A suspension characteristic in which the downward force on the rear of a vehicle, caused by the transfer of a vehicle's weight when accelerating, is resisted.

ASD Relay - When there is no ignition signal(2.5/3.0) or no cam or crank reference signal(3.3/3.8) present and the ignition key is turned to the run position the ASD relay interrupts power to the fuel pump, injectors, coil, and Heated Oxygen Sensor.

ASE - National Institute for Automotive Service Excellence - an independent, non-profit organization dedicated to improving the quality of automotive service and repair through voluntary testing and certification of automotive technicians.

Aspect Ratio - A ratio between two measurements. Aspect ratios are most commonly used to describe the ratio between the height and width of a tire. A lower aspect ratio implies a shorter tire with a wider tread.

Automatic Transmission  (A/T) - A transmission which automatically selects the appropriate gear without any input from the driver. Gears are chosen according to the speed of the vehicle and load on the engine. Automatic transmissions are either hydraulic or electric operated.

ATDC -  After Top Dead Center

ATF -  Automatic Transmission Fluid

Automobile Emissions: Certain impurities that may enter the atmosphere during vehicle operation, such as
hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOX).

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B

B-Pillar - The roof support on either side of a vehicle, situated between the front and rear side windows. Some vehicles, such as late-model Chevrolet Camaros, are not equipped with B-pillars.

Balance Shaft - A shaft in a modern engine that is designed so that, as it rotates, it reduces or cancels out vibrations. Balance shafts are becoming increasingly popular in the design of new engines.

Ball Joint - A flexible joint having a ball-and-socket type of construction. Ball joints are used primarily in a vehicle's front suspension because they can accomodate a wide range of motion.

Barometric Pressure (BARO) - The pressure exerted by the weight of the earth's atmosphere, equal to
one bar, 99.97 kPa, or 14.5 psi at sea level. Barometric pressure changes with the weather and with
altitude. Since it affects the density of the air entering the engine and ultimately the air/fuel ratio,
some computerized emissions control systems use a barometric pressure sensor so that the spark
advance and exhaust gas recirculate (EGR) valve flow can be regulated to control emissions more
precisely.

BBDC -  Before Bottom Dead Center

BCM - An abbreviation for body control module.

BDC - Bottom Dead Center

Belts - A system where the rotating motion of the engine is transmitted to wheels or pullies via a leather or rubber belt. Most modern vehicles use a belt drive system to transmit energy to air conditioning compressors, power steering pumps, alternators, and even water pumps. V-belts are simple rubber belts with a V-shaped surface which runs around the belt. Multi-V or Serpentine belts consist of 3 or more small V-shaped grooves which run around the belt, and may power all the engine's accessories. Cogged belts consist of a number of rubber grooves or cogs which run across the surface of the belt, and are commonly used to drive components such as camshafts (timing belts) and superchargers.

Bench Bleeding - A procedure used to bleed the air from a new or rebuilt master cylinder before it is installed in the vehicle.

BHP - An abbreviation for brake horsepower.  A measurement of horsepower (hp) delivered at the engine
crankshaft. A prony brake or an engine dynamometer is used to determine brake horsepower.

Black Smoke - The exhaust that is produced when the air/fuel mixture is too rich.

Blowby - Byproducts of combustion, mostly hydrocarbons, that leak out of the combustion chamber, past the
piston and piston rings, into the crankcase during the compression and power strokes. In modern engines, blowby vapors are drawn into the intake through the positive crankcase ventilation (PCV)system and are burned in the engine.

Blue Smoke - An exhaust produced when oil has contaminated the air/fuel mixture.

Bog - To lose power and momentarily faulter when coming off the line.

Boost - The increase in intake manifold pressure, produced by a turbocharger or supercharger.

Bored and Stroked - A combination of an enlarged cylinder bore and a lengthened piston stroke to increase an
engine's displacement.

Brake Bias - The distribution of a car's braking power between the front and rear wheels. For maximum braking efficiency, brake bias should be set so that all four wheels are held to just before the point of locking-up.

Brake Fade - A term used to describe the braking condition in which, as brakes heat up under heavy use, their effectiveness begins to diminish.

Brake Switch - In order to illuminate the brake lights, a brake pedal operated "Brake Switch" is provided to operate the vehicle's stop lamps. In addition to lighting the conventional rear lights, the switch also operates the center high mounted stop lamp, that became mandatory on later models. Cruise control equipped vehicles also utilize a vacuum release valve. In this case, both the vacuum release valve and the stoplight switch are actuated by movement of the brake pedal.

Brake Torquing - A procedure used to improve the off-the-line acceleration of a car equipped with an automatic transmission, by depressing the brake pedal with the left foot and the accelerator pedal with the right foot. Doing this allows the driver to increase the rpm of the engine before moving forward.

Breathing - A term used to describe an engine's ability to fill its cylinders with air-fuel mixture and then discharge the burnt exhaust gases. In general, the more air-fuel mixture an engine burns the more power it produces. To improve the breathing ability of an engine is to reduce the restrictions of its intake and exhaust systems.

BSFC - An abbreviation for brake specific fuel consumption.

BTDC - Before Top Dead Center

Bushing - A simple suspension bearing that accommodates limited rotary motion, typically made of two steel tubes, on inside the other, bonded to a sleeve of rubber between them. The compliance of the bushing in different directions has a great effect on ride harshness and handling. Polyurethane is a common substitute to rubber in the construction of high-performance bushings

Bypass Valve - A general term for a valve that lets liquid or air to circumvent an obstruction. For example, a coolant bypass valve allows a small amount of engine coolant to circulate passed the thermostat when it is closed.

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C

Cable - An assembly of two or more wires that may be insulated or bare.

CAFE - An acronym for Corporate Average Fuel Economy.

Calibrate - To check, test, or adjust the initial settings of a unit or system.

Caliper - Non-rotational components of disc brakes that straddle the disc and contain hydraulic components
forcing the brake pads against the rotor to slow or stop the vehicle.

Cam Follower - A term often used for valve lifter.

Camshaft - A shaft having lobes driven by the crankshaft via gears, chains, or belts that, in turn, opens and closes the intake and exhaust valves at proper intervals.

Camshaft Duration - The amount of time, measured in degrees of crankshaft rotation, an intake or exhaust valve is held open.

Camshaft Lift - How far a valve is pushed open, as determined by the height of the cam lobe and the geometry of the rocker arms on a push rod engine, or the cam followers on an overhead cam engine.

Camshaft Reference Sensor - The Camshaft Reference Sensor is mounted on the top of the engine timing chain cover and reads camshaft position by sensing slots on the cam sprocket.  This information is used to make sure the fuel injectors & ignition are synchronized.

Canister Purge Relay - The Canister purge solenoid is controlled by the computer .  When the engine is below 150degeees F the solenoid energizes and prevents vacuum from reaching the charcoal canister valve.  When the temp exceeds 150^F the solenoid is de-energized and fuel vapors are routed to the throttle body.

Carbon Dioxide (CO2) - A harmless, odorless gas composed of carbon (C) and oxygen (O); a product of complete combustion.

Carbon Monoxide (CO) - An odorless gas composed of carbon (C) and hydrogen (H), formed by the incomplete combustion of any fuel containing carbon. This major air pollutant is potentially lethal if inhaled, even in small amounts.

Carbon Tracks - A condition where there is a carbon build up, or track, running from one point to another, acting as an electrical circuit and thereby causing a short circuit.

Cardan Joint - A universal joint having two yokes at right angles to each other, with a cruciform-shaped joint in the middle.

Carrier - A part that holds, positions, moves, or transports another part or parts.

Carrier Bearing - A bearing that supports the ring-gear carrier in the differential.

Cast Iron - A term used for a family of cast ferrous alloys containing at least 2% carbon, plus silicon and sulfur; may or may not contain other alloy elements.

Catalytic Converter - An automotive exhaust-system component, made of stainless steel, containing a catalyst to reduce oxides of nitrogen (NOX), and/or hydrocarbon (HC), and carbon monoxide (CO), in tailpipe emissions.

Celsius - The metric scale for temperature where water (H2O) freezes at 0°C and boils at 100°C.

Centimeter - A metric unit of linear measure equal to 0.3937 inch.

Centrifugal Clutch - A clutch that utilizes a centrifugal force to apply pressure against a friction disc in proportion to  the speed of the clutch.

Centrifugal Supercharger - A mechanically driven, forced-induction system using centrifugal force to increase air pressure.

CFM - An abbreviation for cubic feet per minute.

Charge/Temp Sensor - The Charge/Temp Sensor is a device mounted in the intake manifold which measures the temperature of the air fuel mixture and reports it to the computer.

Chassis Dynamometer(Dyno) - A drive-on device, used to measure net road horsepower and torque, delivered by the drive wheels.

Check Engine Light - A warning light, generally located in the instrument cluster, that indicates a potential engine or system problem.  Also referred to as a MIL Light or Power Loss light.

Chime Module -  The chime module is a device that emits a tone or buzz when fed 12v+.  It is used in warning systems for such things including key in ignition, left lights on, or door a jar.

Chrome Steel - A steel alloy that contains chromium.

Circuit Breaker - A Switch which protects an electrical circuit from overload by opening the circuit when the current exceeds a predetermined level.  Some are reset manually while others automatically reset themselves.

Clearance - The space between mating parts, such as between a journal and a bearing, that allows freedom of
movement or prevents interference.

Clock Spring - A device, located between the steering column and steering wheel, that conducts electrical signals in an air-bag system to the module, while allowing steering-wheel rotation. This provides electrical continuity in all steering-wheel positions.

Clutch Disc - Circular-shaped component, with a friction facing on each side, that transfers power from the flywheel and pressure plate to the splined clutch shaft.

Clutch Release Bearing - A component, attached to the clutch-release fork, that contacts and then moves the release levers when the clutch pedal is depressed.

Coefficient of Drag (Cx) - A measure of the air resistance of a moving vehicle; a measure of how much air is moved as the vehicle moves from one point to another.

Coil (Ignition) - The coil is more or less a voltage transformer.  The coil takes 12 volts DC and steps it up to anywhere from about 20,000v to 40,000v to fire the spark plugs.

Cold-Start Injector - An electronic fuel-injection system that supplies extra fuel to the engine for cold starting.

Compression - 1.)The process of squeezing a vapor (gas) into a smaller space.  2.)The upward stroke of a piston that compresses the air/fuel mixture into the combustion chamber prior to ignition.

Connecting Rod - A component used to attach the piston, with pin, to the crankshaft rod journal.

Connecting Rod Cap - The half-round, lower, bolt-on portion of the connecting rod.

Constant-Velocity Joint - Two universal joints, closely coupled, so their acceleration-deceleration effects cancel each other out.

Coolant Temp Sensor - The Coolant Temp Sensor is a device which monitors the coolant temperature and reports it to the computer.  This sensor is usually found in the thermostat housing.

Cowl Air Intake - The inlet at the base of the windshield that allows outside air to enter the heater/air-conditioning system, or driver/passenger compartment of the vehicle.

Crankshaft Reference Sensor - The Crankshaft Reference sensor is mounted on the bell housing of the transmission and sends information about the position of the crankshaft to the computer.  This sensor is found on the 3.3l and 3.8l engines.

Cubic Inch (ci) - An English measure for volume equal to 16.39 ccs.

Cylinder Block - The basic framework of an engine to which all other parts and assemblies are installed or attached.

Cylinder Head - That part of the engine that covers the cylinders and pistons.

Cylinder-Head Gasket - The gasket used to seal the head to the block to promote compression and to ensure a leak-free bond.

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D

Detonation Sensor(Knock Sensor) - The Detonation Sensor generates a signal when spark knock occurs in the combustion chambers.  This information is sent to the computer and in turn the spark advance is modified to eliminate detonation.

Displacement - The volume within an engine's cylinders, usually expressed in cubic centimeters (cc).

Distance Sensor - The Distance Sensor is located in the transmission extension housing on the passenger side of the transmission.  This sensor is driven by the passenger half shaft and information about vehicle speed is sent to the computer and the computer takes this information and compensates for such conditions as a closed throttle decel or a normal idle.

Distributor Timing - A term used for ignition timing.

DOHC - An abbreviation for dual overhead camshaft.

Dowel - A pin inserted in an object or part to aid in the alignment of another object or part.

Drive Axle - An axle or axle shaft that transmits power to the drive wheels.

Drive Belt - Flexible belt or belts used to connect a drive pulley on the crankshaft to the coolant pump and accessories. Two basic types of drive belts are the serpentine or multiple-ribbed belt and the V-belt.

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E

E85 - A fuel blend of 85% ethanol and 15% gasoline.

ECM - An abbreviation for electronic control module.

EFI - An abbreviation for electronic fuel injection.

EGR Diagnostic Solonoid(California) -

EGR valve - An abbreviation for exhaust gas recirculation valve. A valve, generally vacuum operated, to regulate the exhaust gas flow into the intake manifold.

Emission Controls - The components that are directly or indirectly responsible for reducing air pollution, including crankcase emissions, evaporative emissions, and tailpipe emissions.

Emissions - Unwanted, harmful chemicals and chemical compounds that are released into the atmosphere from
a vehicle, especially from the tailpipe, crankcase, and fuel tank including unburned hydrocarbons, carbon
monoxide, oxides of nitrogen, particulates, and sulfur.

End Gap - The distance between the ends of a piston ring.

Engine Rebuild - To perform an extensive engine repair including machining,  reboring, and honing to
factory-stock specifications.

Exhaust Emissions - Pollutants identified by clean air legislation as being harmful or undesirable, including lead,
unburned hydrocarbons, carbon monoxide, and oxides of nitrogen.

Exhaust Gas - The burned and unburned gases that remain after combustion.

Exhaust Manifold - A component, generally of cast iron, with passages of unequal lengths that carry the exhaust
gases from the exhaust ports to the header of the exhaust system.

Exhaust System - The tubing, mufflers, and catalytic converters that direct exhaust gases from the engine to the
atmosphere.

Exhaust Valve - Valve that, upon opening, allows the burned gases to leave the combustion chamber during the
exhaust stroke.

Extension Housing - An aluminum or iron casting that encloses the transmission output shaft and supporting
bearings.

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F

Fuel Injector - The fuel injector is a solenoid driven by the computer.  The computer based on other inputs determines when and how long the injector is to operate.  When the solenoid is energized a spring loaded ball moves allowing fuel to pass it and enter the combustion chamber.  Due to the high pressure of the fuel a fine spray in the shape of a cone is formed.

Fuel Pump - An electrical motor usually located in the gas tank that pumps fuel to the injectors.  Power to the fuel pump is provided by the ASD relay.

Fuel Pressure Regulator - The Fuel Pressure Regulator is a device which maintains constant fuel pressure to the injectors.  The regulator uses a spring loaded rubber diaphragm to uncover a fuel return port.  When the fuel pump is energized the fuel flows past the injectors to the regulator and is restricted from flowing any further by the blocked return port.  When fuel pressure reaches a predetermined point the diaphragm opens to let some of the fuel through.  The spring and diaphragm will move up and down to keep the fuel pressure at a constant.

Fuel Tank Sending Unit - Sends information on fuel level to the gas gauge.  Also sends the same info to the Low Fuel Relay.

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G

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H

Hall Effect Pickup - The Hall Effect Pickup is located inside the distributor on 2.2/2.5L engines and sends the engine rpm & ignition timing data to the computer which in turn advances or retards the timing as required.

Horn Relay - When the Horn relay receives an electrical signal from the horn switch it energizes allowing the connection to the horns to be completed.  The relays purpose is to handle the higher amperages the switch was never designed to handle.

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I

I.D. - An abbreviation for internal diameter or inside diameter.

Idle - The engine speed with no load and the accelerator pedal fully released.

Idler Pulley - A pulley that is used to adjust the belt in a belt drive system.

Idle Speed - The speed at which an engine idles in revolutions per minute(rpm), usually between 600 and 850
rpm. The idle speed is specified on the underhand emissions decal.

I-4 - An abbreviation for an inline four-cylinder engine.

Ignition - The firing of a spark plug to ignite the air/fuel mixture in the combustion chamber.

Ignition Advance - The moving forward, in time, of the ignition spark relative to the piston position.

Ignition Coil - A transformer containing a primary and secondary winding that acts to boost the battery
voltage of 12 volts to as much as 30,000 volts to fire the spark plugs.

Ignition Reference Pickup -

Ignition Switch - A multi-position switch that is the power distribution point for most of the vehicle's primary
electrical systems. The spring loaded START position provides momentary contact and automatically moves to
the RUN position when the key is released. The other switch detent positions are normally ACCESSORIES,
LOCK, and OFF.

Ignition Timing - The timing of the spark, expressed in crankshaft degrees, in relation to top dead center.

Impeller - A rotor that transmits motion such as a centrifugal pump, supercharger, turbine, or fluid coupling.

Inch-Pound - An English measure of torque.

Independent Suspension - A suspension system by which a wheel on one side of a vehicle can move vertically
without affecting the wheel on the other side, and wheel jounce or rebound travel of one wheel does not directly
affect the movement of the opposite wheel.

Input Shaft - The transmission shaft that receives power from the engine.

Intake Manifold - A metal component used to duct: 1)The air/fuel mixture from the carburetor to the intake ports. or 2).Air in an injected engine to the intake ports.

Intake Stroke - A downward stroke of a piston that draws the air/fuel mixture into the cylinder.

Intake Valve - A valve that opens to admit the air/fuel mixture.

Intercooler - A radiator like heat exchanger between the supercharger or turbocharger and the engine to cool the air/fuel mixture.

Intermittent Wiper Control Unit -

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J

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K

K-car - A compact front wheel drive vehicle introduced by Chrysler in the early 1980s.

Keeper Grooves - The grooved area on a valve stem to accommodate the keepers.

Keepers - Key like, tapered metal locking devices used to hold valve retainers in place on the valve stem.

Knock - A noise within an engine generally caused by detonation or pre ignition.

Knock Sensor - A sensor that signals the engine control computer when detonation is detected, momentarily retarding ignition timing until detonation ceases.


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L

L-Body - A compact front wheel drive vehicle introduced by Chrysler in the late 1970s.

Lapping - A valve-grinding process using a paste-like grit on the face of the valve.

Lapping Compound - A paste-like grit used for lapping valves.

Leaded Gasoline - Gasoline to which a small amount of tetraethyl lead is added to improve engine performance and reduce detonation, a practice no longer allowed due to EPA regulations.

Lean - A term often used for lean mixture or lean out.

Lean Mixture - An air/fuel mixture with too much air.

Limited-Slip Differential - A differential having special friction mechanisms tending to keep both rear-axle shafts rotating at the same speed, regardless of unequal tire-to-road surface friction.

Lock up Torque Convertor Solenoid - The solonoid that controls the lock-up function of the torque converter in an automatic transmission having a mechanical clutch that locks at cruising speeds.

Long Block - An assembled engine block that contains all of the components from the intake manifold to the exhaust ports.


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M

Manufacturer Recall - Automobile manufacturers issue recall notices to inform owners of car defects that have come to the manufacturer's attention. Recalls also suggest improvements that can be made to improve the safety of a particular vehicle. Most manufacturer recalls can be repaired at no cost to you.

MAP(manifold absolute pressure) Sensor
- The Manifold Absolute Pressure(MAP) sensor is a device which monitors manifold vacuum.  This sensor reports information on manifold vacuum condition and barometric pressure to the computer.  The information from this sensor and various others is used to adjust the air/fuel mixture.
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N

Naturally Aspirated - An engine that uses atmospheric pressure to force the air into the cylinders.

Needle Bearing - A bearing that contains needle like rollers.

Neutral Safety Switch - An electrical  switch used on vehicles equipped with automatic transmissions to open
the starter control circuit when the transmission shift selector is in any position except PARK or NEUTRAL. Also known as neutral start switch.

Nitrogen - A colorless, odorless, tasteless gas that makes up 78% of the atmosphere and is part of all living
tissues.

Nitrogen Oxide - Any chemical compound of nitrogen and oxygen (NOX) as a by-product of combustion that
forms smog in the presence of sunlight.

Nitrous - A term used for nitrous oxide.

Nitrous Oxide - A non-flammable, non explosive gas (N2O) used as an oxidizing agent with gasoline or methanol to increase the rate and efficiency of combustion thereby increasing the horsepower.

Normally Aspirated - An engine that is not equipped with a forced means of inducing air.

NOS - A popular manufacturer of nitrous oxide injection systems.

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O

Observed Horsepower - The brake output of an engine as observed on a dynamometer.

Octane - A gasoline's ability to resist detonation. The higher the octane number, the greater the fuel's resistance
to detonation.

Octane Requirement - The minimum octane rating of a fuel required to operate an engine without a spark
knock.

O.D. - An abbreviation for outside diameter.

Odometer - A mechanical or electronic counter in the speedometer that indicates trip or total miles accumulated on the vehicle.

Ohmmeter - An analog or digital instrument used to measure electrical resistance in ohms.

Oil Clearance - The small space between the main bearing and crankshaft journal,usually 0.001 to 0.003 inch (0.025 to 0.076 mm), for lubricating oil to circulate.

Oil Control Ring - The bottom piston ring that scrapes the oil from the cylinder wall.

Oil Filter - A component, located near the oil pump, that removes abrasive particles from the motor oil by a
straining process as the oil circulates through the lubrication system.

Oil fouled Plug - A wet, oily deposit on a spark plug that may be caused by oil leaking past worn piston rings.

Oil Gallery - Passages drilled or cast into the cylinder heads, engine block, and crankshaft to receive pressurized oil from the oil pump for distribution throughout the engine.

Oil Pan - A removable part of the engine that contains the oil supply.

Oil Pressure - The pressure, 15 to 75 psi (103 to 517 kPa), developed by the oil pump to force oil through the lubrication system.

Oil-pressure Gauge - An instrument used to display the oil pressure of the engine lubrication system.

Oil Pressure Switch - An electronic switch used to measure the oil pressure and send the readings to the ECU and oil pressure gauge.

Oil Pump - A pump, driven directly or indirectly by the camshaft, that draws oil from the oil pan and forces it, under pressure, through the engine lubrication system.

Oil Ring - Piston ring that scrapes oil from the cylinder wall to control cylinder wall lubrication and prevent excessive oil loss past the piston and into the combustion chamber.

Ohm Meter - An instrument used for measuring the resistance, in ohms, in an electrical circuit

O-ring - A round ring having a square or round cross section used as a seal, such as at the end of a hydraulic
line.

Overdrive - A transmission having a ratio of less than 1:1 where the output shaft turns at a greater rpm than does the input shaft.

Overdrive Ratio - A ratio identified by the use of a decimal point, such as 0.80, indicating less than one driving input revolution compared to one 1.0 output revolution of a shaft, or 0.85:1.0.

Overlap - The interval of valve timing when the intake valve starts to open before the exhaust valve is fully closed.

Oversize (OS) - A part that is larger than the original to make up for wear and machining.

Oxide - A compound formed when a substance combines with oxygen.

Oxides of Nitrogen (NOX) - Harmful, gaseous emissions of an engine composed of compounds of nitrogen and
varying amounts of oxygen which are formed at the highest temperatures of combustion.

Oxygen - A colorless, gaseous, tasteless, element (O) that makes up 21% of the atmosphere.

Oxygen Sensor - The Oxygen Sensor is a device which produces an electrical voltage when exposed to the oxygen present in exhaust gases.  This information is transmitted to the computer which in turn varies the pulse width of the injectors accordingly.  This sensor from '87 on has been referred to as a Heated Oxygen Sensor

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P

          Primary Circuit - Is the low voltage side of the ignition system which consists of the ignition switch, ballast
                                        resistor or resistance wire, bypass, coil, electric control unit and pickup coil as well as the
                                        connecting wires and harnesses

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Q

Quad Valve Head - A cylinder head with four valves, two exhaust and two intake, per cylinder.


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R

Radiator - A heat exchanger used to remove heat from the coolant in the cooling system containing a vertical- or horizontal finned tubing section connected between two tanks.

Radiator Fan Relay -

Rear Window Defrost Relay -

Relay - A switch which automatically opens and/or closes a circuit

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S
SMEC(Single Module Engine Controller) -

SBEC(Single Board Engine Controller) -

SMPI - Acronym for "sequential multi-point electronic fuel injection."
 

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T

Tachometer - An instrument that indicates the number of revolutions per minute at which the engine is turning. Tappet A pivoting actuator than opens and closes cylinder valves.

Thermostat - A temperature sensitive mechanical device found at the coolant outlet of an engine that
expands (opens) or contracts (closes) to control the amount of coolant allowed to leave the engine,
based on its temperature.

Throttle Body - A housing containing a valve to regulate the airflow through the intake manifold. The throttle-body is usually located between the air cleaner and the intake plenum.

Throttle-Body Fuel Injection - A form of fuel injection in which the injectors are located at the engine's throttle-body, thereby feeding fuel to more than one cylinder. Such an arrangement saves money by using fewer injectors; but because it routes both fuel and air through the intake manifold, it eliminates some of the tuning possibilities offered by port fuel injection.

Throttle Body Temperature Sensor - The throttle body temperature sensor is a device in the throttle body that measures the throttle body temperature which is the same as a fuel temperature.  This information is sent to the computer to help compensate the mixture for a hot start situation.

Throttle Position Sensor - The Throttle Position Sensor is mounted on the throttle body and senses the angle of the throttle blade opening.  The voltage that the sensor produces depends on the position of the throttle blade.  This information is sent to the computer and is used along with data from other sensors to adjust the air/fuel mixture.

TCM - Transmission Control Module

Timing - Timing refers to the delivery of the ignition spark, or the opening and closing of the engine valves,
depending on the piston's position, for the power stroke. The timing chain is driven by a sprocket on the
crankshaft and also drives the camshaft sprocket.

Toe Steer - The changes in the direction of a wheel that occur without driver steering input. Toe steer can be caused by ride steer or by deflections in suspension components caused by the stresses of cornering, accelerating, and/or braking on smooth and bumpy roads.

Torque - The rotational equivalent of force, measured in pound-feet.

Torque Converter - A particular kind of fluid coupling with a third element added to the usual input and output turbines. Called ""the stator,"" this additional element redirects the churning fluid against the output turbine, increasing torque. This torque increase, however, is achieved at the expense of rpm and efficiency.

Torque Steer - A tendency for a car to turn in a particular direction when power is applied. Torque steer is common in front-drive cars because reaction forces created in the half-shafts can generate uneven steering forces in the front tires.

Tune-Up - The inspection, testing, and adjusting of an engine; the replacement of any parts required to
ensure maximum performance.  Some of the parts that may be replaced in a tune-up are distributor cap, wires, spark plugs, PVC valve, and filters.

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.

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U

Understeer - A handling condition in which the slip angle of the front tires is greater than the slip angle of the rears. An understeering car is sometimes said to push, because it resists turning and tends to go straight.

Unleaded Gasoline - Gasoline that contains less than 0.0018 ounces (0.05 grams) of lead per gallon (3.785 liters).
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V

Vacuum - An enclosed space from which all air has been removed, having an absolute atmospheric
pressure of near zero.

Vacuum Advance - A device which advances the ignition timing in response to increased engine vacuum

Vacuum Booster - A power-brake actuating mechanism that uses vacuum on one side of a diaphragm as a power source to amplify braking force.

Vacuum Gauge - An analog or digital instrument used for measuring vacuum.

Valve - A circular-stemmed device used to control the flow of air/fuel mixture in and the flow of burned gasses out of the engine.

Valve Clearance - A term used for valve lash.

Valve Face - The tapered section of the valve head making contact with the valve seat.

Valve Angle - The angle at which the valve face is machined.

Valve Float - A high-rpm engine condition in which the valve lifters lose contact with the cam lobes because the valve springs are not strong enough to overcome the momentum of the various valvetrain components. The onset of valve float prevents higher-rpm operation. Extended periods of valve float will damage the valvetrain.

Valve Guide - The bore in the cylinder head through which the valve stem passes.

Valve Job - The reconditioning of a cylinder head, including the valves.

Valve Keeper - A small part that fits into the retainer groove located near the tip of the valve stem to secure the valve and valve spring.

Valve Lash - The specified clearance between a valve stem end and a rocker arm on an OHV engine or valve stem end and the camshaft on an OHC engine; necessary to allow for heat expansion.valve lift: Distance that the valve moves from the closed to the open position.

Valve Lifter - A cylindrically shaped hydraulic or mechanical device in the valve train that rides on the
camshaft lobe to lift the valve off its seat.

Valve Overlap - The time that the closing of the exhaust valve overlaps the opening of the intake valve at the end of the exhaust stroke and at the beginning of the intake stroke, when the intake and exhaust valves are partially open at  the same time depending on the spacing of the lobe centers on the camshaft and the cam's duration.

Valve Retainer - A term used for valve keeper or valve key.

Valve Seat - The ring of hard metal to which the valve seals.

Valve-seat Insert - A replacement valve seat.

Valve Spring - A small coil spring that closes the valve and keeps the lifter in contact with the camshaft.

Valve Timing - The actual opening and closing of the valves in relationship to the number of degrees of
crankshaft rotation.

Valvetrain - The many parts making up the valve assembly and its operating mechanism.

Viscosity - The resistance of a fluid to flowing.

Viscosity Grade - The numerical rating of a fluid's resistance to flow.

Viscosity Index - A number to indicate the change in viscosity of an oil when heated.

Viscosity Rating - A numerical indicator of the viscosity of an engine oil established by the American Petroleum
Institute.

Viscous Coupling - A particular kind of fluid coupling in which the input and output shafts mate with thin, alternately spaced discs in a cylindrical chamber. The chamber is filled with a viscous fluid that tends to cling to the discs, thereby resisting speed differences between the two shafts. Viscous couplings are used to limit the speed difference between the two outputs of a differential, or between the two axles of a car.

Volt Meter - An instrument used to read the pressure behind the flow of electrons.

Voltage Regulator - The Voltage Regulator is a device used in the electrical system to keep voltage at a predetermined value.  Usually around 13.5v DC or so depending on application.

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W

Warp - A slight twist or curve in a surface.

Wastegate - A turbocharger relief valve to prevent the buildup of too much pressure.

Water Pump - A device, usually located on the front of the engine and driven by one of the accessory drive
belts, that circulates the coolant by causing it to move from the lower radiator-outlet section into the engine by
centrifugal action of a finned impeller on the pump shaft.

Weather-pack Connector - A connector, having rubber seals on the terminal ends and on the covers of the
connector half, used on computer circuits to protect the circuit from corrosion, which may result in a voltage drop.

Wheel Hop - An undesirable suspension characteristic in which a wheel (or several) moves up and down so violently that it actually leaves the ground. Wheel hop can be caused by many problems, including excessive unsprung weight, insufficient shock damping, or poor torsional axle control.

Wheelbase - The distance between the centers of the front and rear wheel axles as viewed from the side of the car.

Windage Tray - A metal meshed screen in the oil pan to deflect oil away from the crankshaft.

Wrist Pin - A pin used to attach the connecting rod to the piston.

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X

Xenon - A colourless, odourless gas used in electric luminescent tubes to provide a bright light. Xenon is often used in timing lights because it produces enough light to use in daylight.

Xylene - A chemical solvent (C8H11) used to remove grease and paint.
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Y

 
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Z

Zener Diode - A diode often used in electronic voltage regulators.

Zerk Fitting - A nipple-like lubrication fitting through which grease is applied to a chassis or suspension joint with a grease gun.

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