Automotive Terminology & Definitions

an increase in velocity or speed.

in automotive terminology, a substance added to a liquid, such as engine oil, transmission fluid, gear oil or coolant to enhance its properties.

a vehicle that combines new engine/power/drivetrain systems to significantly improve fuel economy. This includes hybrid power systems and fuel cells, as well as some specialized electric vehicles.

a specified space between two components. Space or gap between spark plug electrodes, motor and generator armatures Ind field shoes. The space or gap between the compressor drive hub and pulley assembly.

a system that provides fresh air to the exhaust system under controlled conditions to reduce emissions. The air source can be a pulse-air pump or an electrically or belt driven pump. Upstream air injection goes into the exhaust manifold to assist in after-burning HC laden exhaust gases. Downstream air injection goes into the oxidation bed of the catalytic converter to help oxidize HC and CO emissions.

device to produce a flow of air at higher-thanatmospheric pressure. Normally referred to as a thermactor air supply pump.

the proportion of air to fuel by weight in the fuel mixture drawn into the engine.

mixture containing mostly metals. For example, brass is an alloy of copper and zinc. Steel contains iron and other metals, but also carbon

as defined by the Energy Policy Act, any dedicated, flexible-fuel, or dual-fuel vehicle designed to operate on at least one alternative fuel.

alternative fuel, also known as non-conventional fuels, is any material or substance that can be used as a fuel, other than fossil fuels, or conventional fuels of petroleum (oil), coal, propane, and natural gas. The term "alternative fuels" usually refers to a source of which energy is renewable.
Methanol, denatured ethanol, and other alcohols; mixtures containing 85% or more by volume of methanol, denatured ethanol, and other alcohols with gasoline or other fuels; natural gas; liquefied petroleum gas; hydrogen; coal-derived liquid fuels; non-alcohol fuels (such as biodiesel) derived from biological material; and electricity. 'P-Series' fuels were added to this list since the original definition in EPAct.

the temperature of the medium surrounding an object

a material such as ethylene glycol which is added to water to lower its freezing point; used in an automobile's cooling system.

100% (neat) biodiesel.

a blend of biodiesel fuel with petroleum-based diesel where 20% of the volume is biodiesel.

a soft bearing alloy used in engine bearings.

pressure created by a blockage or restriction in an exhaust system.

the sudden combustion of gasses in the intake or exhaust manifold, resulting in a loud explosion.

a weighted shaft used on some engines to dampen or reduce vibration.

resistor in the primary side of the ignition system hat is used to reduce voltage by approximately 4-5 volts.

batteries are the principal energy storage devices for hybrid electric vehicles (HEVs). Desirable attributes of high-power batteries for HEV applications are high-peak and pulse-specific power, high specific energy at pulse power, a high charge acceptance to maximize regenerative braking utilization, and long calendar and cycle life. Developing methods/designs to balance the packs electrically and thermally, developing accurate techniques to determine a battery's state of charge, and developing abuse-tolerant batteries, and recyclability are additional technical challenges.

bottom dead center, when the piston is at its lower limit in the cylinder bore.

the lower half of the bearing saddle. It is removable, as in main cap or rod cap.

the space between a bearing and its corresponding component's loaded surface. Bearing clearances are commonly provided to allow lubrication between the parts.

the bearing is slightly larger at its parting lines so that when the two halves of the bearing are tightened together, the bearing seats firmly in its bore. This keeps the bearing from rotating.

the bearing surface area of a bearing, it is usually made up of an alloy of several metals, including lead.

the condition in which the distance across the outer edges of the bearing insert is slightly greater than the diameter of the housing bore. A bearing is spread slightly apart at its paning halves so that it snaps into place in its bore and remains there during assembly.

the degrees of crankshaft rotation just before the piston in a specific cylinder reaches TDC, the highest point in its vertical travel on the compression stroke. On most vehicles, spark occurs a certain number of degrees of crankshaft rotation BTDC.

a vehicle with two separate fuel systems designed to run on either an alternative fuel, or gasoline or diesel, using only one fuel at a time. Bi-fuel vehicles are referred to as "dual-fuel" vehicles in the Clean Air Act Amendments and Energy Policy Act.

the casting made up of cylinders and the crankcase.

the unburned fuel and products of combustion that are forced past the piston rings and into the crankcase during the combustion stroke.

term used when a turbocharger increases the air pressure entering an engine above atmospheric pressure.

a precision measuring instrument used to measure the diameter of a bore.

a cylindrical hole.

the part of a piston that fits around its pin.

when the piston is at its lower limit in the cylinder bore.

power developed by an engine as measured at the flywheel or crankshaft.

the ratio of engine fuel consumption to power output. It is a measure of engine efficiency.

see 'before top dead center'.

a bearing that supports the camshaft journal. On some engines it is full round and pressed in place. On some OHC engines the camshaft bearing is made up of two shells like a connecting rod bearing.

on OHC engines the equivalent of a rocker arm.

the bearing area of a camshaft.

the eccentric on a camshaft that acts on lifters or followers and in turn, other valvetrain components as the camshaft is rotated, to open the intake and exhaust valves.

a magnetic, halI effect, optical or magneto resistive sensor usually mounted internally in the engine to inform the ECM or PCM of piston position on the intake stroke for timing and synchronization of sequential fuel injection.

the sprocket on a camshaft that is turned by a chain or belt from the crankshaft. The camshaft sprocket has twice as many teeth as the crankshaft sprocket.

A product of combustion that has become an environmental concern in recent years. CO2 does not directly impair human health, but is a greenhouse gas that traps the Earth's heat and contributes to the potential for global warming.

a colorless, odorless gas, which is highly poisonous. CO is produced by incomplete combustion. It is absorbed by the bloodstream 400 times faster than oxygen.

a hard or soft nonmetallic element that forms in an engine's combustion chamber when oil is burned.

a device that atomizes air and fuel in a proportion that is burnable in the engine.

metal that is manufactured by pouring it into a mold. It is more porous than forged metal and does not conduct heat as well. It is less expensive to manufacture, however.

an emission control device located in the exhaust system that contains catalysts, which reduce hydrocarbons, carbon monoxide and nitrogen oxides in the exhaust gases.

process of oxidizing unburned hydrocarbons and carbon monoxide by means of a catalytic reaction to reduce pollution.

a device used on carbureted vehicles to reduce the amount of air entering the intake manifold while leaving the amount of fuel unchanged. The purpose of a choke is to richen the mixture enough that a cold engine can still get enough vaporized fuel to start.

electronic feedback system in which sensors provide constant information on what is taking place in the engine; the state of the engine control computer system when it is working normally, at full operating temperature and normal speeds with the oxygen sensor switching. The fuel injection quantity is determined by the set of inputs from the engine control computer's sensors, most specifically the oxygen sensor in the exhaust stream. A closed loop system samples its output and uses that sampling to modify the next inputs.

system in which the fuel/air ratio in the engine is carefully controlled to optimize emissions performance. A closed-loop system uses a fuel metering correction signal to optimize fuel metering.

a Coil-on-Plug ignition system uses one ignition coil for each cylinder attached to the spark plug. The system replaces remote ignition coils and high-voltage ignition wires in a distributorless ignition system.

difficulty of starting an internal combustion engine in cold weather because of gasoline, which evaporates more slowly when it is cold; oil, which gets thicker in cold weather; and the chemical reactions inside the battery, which progress more slowly in cold weather.

enclosure formed by a pocket in the cylinder head and the top of the piston, where the spark plug ignites the compressed air/fuel mixture. The volume of the cylinder above the piston when the piston is at TDC.

the burning of the air/fuel mixture.

a fuel-injection system that uses a single "rail" (fuel line) that maintains constant fuel pressure regardless of injection sequence (also called common rail injection). The engine's electronic timing regulates fuel-injection timing and quantity according to data from sensors on the camshafts and crankshafts so that compression and injection occur independently. Fuel is injected only as needed, which reduces fuel consumption and emissions.

the form of ignition that initiates combustion in a diesel engine. The rapid compression of air within the cylinders generates the heat required to ignite the fuel as it is injected.

ratio of the volume in the cylinder above the piston when the piston is at bottom dead center to the volume in the cylinder above the piston when the piston is at top dead center.

usually the top two rings on a piston, they form a seal between the piston and cylinder wall to compress the air fuel mixture in the cylinder.

the second stroke of the 4-stroke engine cycle, in which the piston moves from bottom dead center and the intake valve is closed, trapping and compressing the air/fuel mixture in the cylinder.

in a solid material, compression is the opposite of tension. In a gas, compression causes the gas to be confined in a smaller area, raising its temperature and pressure.

commonly called the diesel engine, has the highest thermal efficiency of any internal combustion engine. Challenges to improvements include a lower specific power than the gasoline engine; significant particulate matter and nitrogen oxides in the exhaust; and the noise, vibration, and smell of the engine.

the plain bearing shells located in the big end of the connecting rod that support the connecting rod and piston on the crankshaft.

the removable part of the big end of the connecting rod.

a rod that connects the crankshaft to the piston and enables the reciprocating motion of the piston to turn the crankshaft.

a system that uses fuel under pressure to maintain or change the fuel injection area.

the mixture of water and antifreeze used in an engine's cooling system to maintain the engine's temperature throughout Its operating range.

a mechanically or electrically driven propeller that draws air through the radiator.

the system used to remove excess heat from an engine and transfer it to the atmosphere. Includes the radiator, cooling fan, hoses, water pump, thermostat and engine coolant passages.

additives used to inhibit corrosion (e.g., rust) in the fuel system.

distance from the crankshaft main bearing centerline to the connecting rod journal centerline. The stroke of any engine is the crank throw.

unmachined portion of a crankshaft that lies between two crank pins or between a crankpin and main bearing journal.

the lower part of an engine block that houses the crankshaft.

the part of the crankshaft to which the connecting rod is attached.

the bearing areas of a crankshaft are the main and rod journals.

a magnetic, hall effect, optical or magneto resistive sensor usually mounted internally in the engine, externally to the engine or in the distributor to inform the ECM or PCM of crankshaft position, location of No.1 piston, and crankshaft speed for ignition timing and other calculations needed by the system where rpm is an input.

the belt drive pulley mounted on the front of the vibration damper.

a flat machined area that is 90 degrees to the crankshaft main journals. The flange of the thrust main bearing rides against it to control cranksnan end tnrust.

a lower engine part with main and rod bearing journals. It converts reciprocating motion to rotary motion.

a radiator in which coolant enters on one side, travels through tubes, and collects on the opposite side (see downflow radiator).

the bearing is slightly larger at its parting lines so that when the two halves of the bearing are tightened together, the bearing seats firmly in its bore. This keeps the bearing from rotating.

the casting that contains the valves and valve springs, and covers the top of the cylinders.

in engine diagnostic test where the piston in the cylinder to be tested is brought to top dead center (TDC) on the compression stroke and compressed air is pumped into the cylinder through the spark plug hole. Where the air leaks out shows the location of the compression leak. A leakage tester will compare the air leaking out of the cylinder to the amount of air being put into it, expressed as a percentage.

a replacement iron liner that fits into a cylinder bore. It can be either wet or dry. The outside diameter of wet sleeves contacts the coolant.

the walls of the cylinder bore.

round hole in the engine block for the piston.

a device mounted on the front of the crankshaft. It reduces the torsional or twisting vibration that occurs along the length of the crankshaft in multiple cylinder engines. It is also called a harmonic balancer.

the extreme upper or lower position of the crankshaft throw at which the piston is not moving in either direction.

the top of the engine block where the cylinder head is attached.

abnormal combustion of an air fuel mixture. When pressure in the cylinder becomes excessive and the mixture explodes violently, instead of burning in a controlled manner. The sound of detonation can be heard as the cylinder walls vibrate. Detonation is sometimes confused with preignition or ping.

a code that represents and can be used to identify a malfunction in a computer control system.

an accurate casting made by pouring pressurized molten material into a mold or die.

any internal-combustion engine in which air is compressed to a sufficiently high temperature to ignite fuel injected into a cylinder. A diesel engine differs from other internal-combustion engines, such as gasoline engines, in that it employs no ignition devices, such as an electric spark. For this reason, it is often called a compression-ignition engine.

petroleum products normally used as fuel for diesel engines are components of crude oil having heavy hydrocarbons containing at least 12 to 16 carbon atoms per molecule. These heavier fractions are taken from crude oil after the more volatile portions used in gasoline are removed.

a condition by which hot spots in the combustion chamber(s) cause the engine to run on after the key is turned off.

distributorless ignition system in which spark distribution is controlled by the computer.

in DI, fuel is injected directly into the cylinder, as is typical in a diesel engine (also called direct fuel injection). Most other internal combustion engines use either carburetion (in which the air and fuel are mixed long before the air enters the cylinder) or port fuel injection (in which the fuel is injected just in front of the cylinder intake valve).

direct injection (DI) refers to fuel injected directly into the combustion chamber above the piston. Direct Injection has long been used on large diesel engines. Smaller diesels are increasingly adopting direct injection (vs. indirect injection into a pre-chamber). Direct Injection also can be used in spark ignition (generally gasoline) engines instead of port fuel injection - for cleaner emissions, increased full throttle power and potentially for lean-burn operation.

with direct injection spark ignition (DISI) engines, fuel is injected in one of two ways depending on operating conditions. Lean burn operation (at part throttle), injects fuel after the air has entered, causing higher fuel concentration near the injector and spark plug for easy ignition. This is known as stratified charge. The overall air/fuel ratio is lean for better fuel consumption. At full power, fuel is injected at the same time as air (same as for conventional) to promote good mixing. Fuel evaporating in the combustion chamber cools the air slightly for higher volumetric efficiency and power. Since all fuel being injected goes directly into the cylinder, it can be metered more precisely, promoting cleaner emissions.

a fuel injection system wherein fuel is sprayed directly into the combustion chamber, that is, no precombustion chambers or manifold injection.

the volume of a cylinder displaced by the piston as it moves from TDC to BDC (a complete stroke).

the percentages of gasoline that evaporate at various temperatures. The distillation curve is an important indicator for fuel standards such as volatility (vaporization).

the degree to which a vehicle operates properly, including starting, running smoothly, accelerating and delivering reasonable fuel mileage.

a sleeve, that when installed in a cylinder block, does come into contact with coolant.

see 'diagnostic trouble code',

vehicle designed to operate on a combination of an alternative fuel and a conventional fuel. This includes (a) vehicles that use a mixture of gasoline or diesel and an alternative fuel in one fuel tank, commonly called flexible-fuel vehicles; and (b) vehicles capable of operating either on an alternative fuel, a conventional fuel, or both, simultaneously using two fuel systems. They are commonly called bi-fuel vehicles.

the length of time that a valve remains open, measured in crankshaft degrees.

degree of crankshaft rotation during which the primary circuit is on.

a dye which is painted on a valve seat in order to determine seat concentricity. The valve is inserted into the guide, lightly seated, and rotated about 1/8 in. A continuous blue line should appear all the way around the valve face if the valve and seat are mating properly. Open patches or breaks in the line indicate that the seat is not concentric and the low spots are not making contact.

a mixture of 85% denatured ethanol and 15% gasoline, by volume; an alternative engine fuel.

ethanol mixture that contains 93% ethanol, 5% methanol and 2% kerosene, by volume.

ethanol/gasoline mixture that contains 95% denatured ethanol and 5% gasoline, by volume.

a sensor mounted on the EGR valve that signals the engine control computer regarding EGR valve pintle position and EGR flow.

see 'exhaust gas recirculation (EGR) valve',

the ability of the bearing lining material to absorb contaminants.

the casting made up of cylinders and the crankcase.

the electronic computer that controls engine operation. ECM is synonymous with ECA, ECU, SBEC or SMEC. It is less powerful than the PCM or VCM in that it controls only engine operation.

a sensor which works by a negative coefficient thermistor that loses resistance as its temperature goes up (just like the intake air temperature sensor). When the computer applies its 5-volt reference signal to the sensor, this voltage is reduced through a ground circuit by an amount corresponding to the temperature of the engine coolant.

the volume displaced by aIl of the pistons in all of an engine's cylinders.

a device that converts heat energy into mechanical energy.

actual air/fuel ratio divided by the stoichiometric air/fuel ratio. An air/fuel mixture is said to be stoichiometric when fuel combustion consumes all of the initial reacting species in going to completion.

a liquid alcohol made by fermenting sugars derived from starches in plants, such as corn or sugar cane (CH3CH2OH, ethyl or grain alcohol). When denatured (made unfit for human consumption), it can be used as an engine fuel. Can be produced chemically from ethylene or biologically from the fermentation of various sugars from carbohydrates found in agricultural crops and cellulosic residues from crops or wood. Used in the United States as a gasoline octane enhancer and oxygenate, it increases octane 2.5 to 3.0 numbers at 10% concentration. Ethanol also can be used in higher concentration in alternative fuel vehicles optimized for its use.

a fuel oxygenate used as a gasoline additive to increase octane and reduce engine knock.

"EVAP" canister purging is controlled by the engine control computer, which determines when the canister should be purged based on various sensor inputs. When purging is needed the computer operates the purge solenoid, which controls the vacuum to purge the canister. Generally, the purge solenoid is activated when the engine is running above idle speed and at normal operating temperature.

a valve on the line between the EVAP canister and the intake manifold. When the engine is running, under certain operating conditions, the valve opens, fresh air is drawn in through the canister air filter and the air and fuel vapors are drawn into the engine and burned, purging the canister.

a charcoal-filled container with lines to the top of the fuel tank, to the intake manifold and to the air cleaner. The charcoal element adsorbs fuel vapors from the gas tank and stores them until the engine is running at normal operating temperatures and speeds. Then, a valve between the canister and engine opens, fresh air is drawn in through the canister air filter and the air and fuel vapors are drawn into the engine and burned, purging the canister.

an emission control system that prevents HC emissions from escaping the fuel system to atmosphere.

hydrocarbon vapors that escape from a fuel storage tank or a vehicle fuel tank or vehicle fuel system.

a method of controlling emissions from internal combustion engines - primarily Nox - by applying air pollution control technologies to engine exhaust (as opposed to treatments applied to the engine's intake air or during in-cylinder combustion stages).

helps prevent the formation of oxides of nitrogen (Nox) by recirculating a certain amount of exhaust as an inert gas through the intake manifold to keep the peak combustion temperatures below what would form those chemical compounds. The computer determines when and how much exhaust to recirculate based on information from all its other sensors. It then actuates the EGR solenoid, which opens a vacuum circuit or operates an electronic circuit or operates an electronic circuit to actually work the EGR valve. The computer uses a duty-cycle (percentage of on-time) signal to activate the solenoid.

component in the EGR system, used to meter a controlled amount of exhaust gas into the intake air stream.

an emissions control technique that reuses engine exhaust gases as part of the intake air supply to help reduce harmful emissions (especially Nox).

the part of the exhaust system that is fastened to the cylinder head.

the pipe between the exhaust manifold and muffler.

the passage or opening in a four stroke cylinder head for the exhaust valve.

the final stroke in a 4-stroke cycle engine during which the exhaust valve is open and the intake valve is closed, exhausting the combusted gases.

poppet valves in the cylinder head that control the flow of exhaust from the engine.

a basic concept in the way the engine control system works. 'Feedback' refers to the mechanism whereby the computer is able to measure the Oxygen in the exhaust stream and then modify the amount of fuel injected into the intake manifold to optimize exhaust emissions by keeping the air/fuel ratio at stoichiometry.

a Vehicle with a common fuel tank designed to run on varying blends of unleaded gasoline with either ethanol or methanol.

a piston pin that moves in the piston and the small end of a connecting rod. It is held in place by retaining clips in the pin bosses.

a condition in which unvaporized fuel in the intake manifold and/or combustion area, prevents the engine from starting.

as applied to engine valves, refers to a condition wherein the valve is not held tightly on its seat due to a weak valve spring, during the time the cam is not lifting it.

a unit of measurement for torque. One foot pound is the torque obtained by a force of one pound applied to a wrench handle that is 12-in. long; a unit of energy required to raise a weight of one pound, a distance of one foot.

an engine, either gasoline or diesel that uses four strokes: intake, compression, power and exhaust. A firing impulse occurs every two turns of the crankshaft. When this engine is a gasoline engine it is also called an Otto cycle engine after its inventor. A diesel engine is called a Diesel cycle engine for the same reason.

another name for core plug.

ability of a vehicle to operate on either (a) a wide range of fuels blends (e.g., blends of gasoline and alcohol) or (b) two different fuels carried aboard the vehicle (e.g., gasoline and compressed natural gas).

a system that sprays fuel directly into the intake air stream.

an electrically-opened nozzle that sprays finely atomized fuel through its aperture into the intake manifold during a cylinder's intake stroke. On some vehicles, these injections are sequential, on others, the injectors are fired all at once or in banks.

uses intake manifold vacuum, or more properly intake manifold absolute pressure (MAP), to modify the pressure in the fuel rail. The fuel pump can pump more fuel than the engine can use, so the system routes the extra fuel back to the tank through the fuel pressure regulator.

the computer controls the electric fuel pump by energizing the fuel pump relay. It does so by grounding the fuel pump relay coil circuit. The relay then directly supplies power to the fuel pump.

a mechanical or electronic device that draws fuel from the fuel tank and sends it to the carburetor or fuel injection system.

a manifold used to connect fuel injectors to the fuel pump

works by de-energizing the fuel pump relay. This occurs if the engine speed sensor indicates excessive engine speed or if the vehicle speed sensor indicates a certain mph.

fuel delivery (volume) adjustments based on closed loop feedback. values above the nominal value (0%) indicate increased injector pulse width (IPW); values below 0% indicate decreased injector pulse width. Positive percentages indicate richening air/fuel ratio; negative percentages indicate a leaning air/fuel ratio. Short Term Fuel Trim (STFT) is based on current oxygen sensor switching values. Long Term Fuel Trim (LTFT) is a learned value used to compensate for continual deviation of STFT from the nominal value. For example, if STFT continually signals richening the air/fuel ratio, it will reach a value sufficient to increment the LTFT to a richer value.

a multi-dimensional 'map' that correlates engine speed, temperature, load and other factors into a specific spark advance and fuel injection pulse width for that set of conditions. There are several such 'maps' in the computer's hardwired memory. The fine-tuning of the fuel mixture is completed by the signal from the oxygen sensor. On some vehicles, a knock sensor is included to fine-tune the ignition advance to accommodate differences in fuel octane rating and engine wear.

a rotary engine that draws energy from a fuel-air mixture. A compressor raises the pressure and temperature of the inlet air. The air is then moved into a burner, where fuel is injected and combusted to raise the temperature of the air. Power is produced when the heated, high-pressure mixture is expanded and cooled through the turbine.

a material such as artificial rubber, cork, or steel used to seal between parts that would otherwise leak fuel, coolant, lubricants or combustion gases.

an electrically heated wire that helps ignite diesel fuel when a compression ignition engine is cold and the compression process may not raise the air to a high enough temperature for ignition.

a device that reduces the torsional or twisting vibration that occurs along the length of the crankshaft in multiple cylinder engines. It is also called a vibration damper.

an oxygen sensor with a resistance element built into it to shorten the time needed to bring the sensor to operating temperature. Heated oxygen sensors will keep the sensor at operating temperature during idle, low speeds, and in very cold weather. The HO2's heater is on whenever the ignition switch is on.

a combustion chamber shape that resembles a half a globe. The valves are on the sides of the spark plug, which is in the center.

the chemical symbol for the element mercury. Engine vacuum is measured in inches of mercury or in/Hg

abrasive tool for correcting small irregularities or differences in diameter in a cylinder, such as an engine cylinder or brake caliper; to enlarge or smooth a bore with a rotating tool containing an abrasive material.

measurement of an engine's ability to perform work. One horsepower is the energy required to lift 550 pounds 1 foot in 1 second.

the machined bore in a block or head where a bearing will be installed.

controls the amount of air allowed to bypass the closed throttle to keep the engine at the proper idle speed. The computer also controls the idle speed of the engine, depending on engine coolant temperature and the number of accessories such as headlights, air conditioning, etc. that are engaged. The idle air control (lAC) valve controls air flow through a throttle bypass passage by means of a stepper motor, an electric motor that can move to a specific location in its travel. Based on the information from its sensors and the parameters in its memory, the computer sends a duty-cycle (percentage of on-time) signal to the lAC valve motor to open or close the bypass to increase or slow the idle speed. This signal can range from zero to 100 percent, and corresponds to the amount of airflow the computer determines is needed. Displayed on the scan tool as counts or percentage.

characteristic of a solid that enables it to spontaneously ignite. Any liquid with a flash point below 140°F is said to possess ignitability.

transforms the low 12-volt battery ignition primary current into the high voltage secondary current that fires the spark in the plugs. The current through the primary coil windings builds up an electromagnetic field around the ferrous core of the coil. When the current is suddenly shut off, the electromagnetic field collapses and generates the high voltage in the secondary windings.

the computer does not directly operate the ignition coil, because of the comparatively high voltages and currents involved. Instead, it signals the ignition control module when to fire the spark. The (ICM) has a power transistor which turns on the ignition primary circuit to charge the coil by building an electromagnetic field around the ferrous core, and fires the spark by shutting off the current to the primary circuit, aI/owing the field to collapse and generate a high voltage spark current in the coil secondary circuit. The ignition control module typically includes additional internal circuits to perform other functions such as calculating dwell. Some modern systems have dwell and timing control in the PCM regulating the ICM to the duties of an on-off switch for the coil.

a key operated switch located on the steering column, that connects and disconnects power to the ignition and electrical systems.

the components that produce the spark to ignite the air/fuel mixture in the combustion chamber.

refers in crankshaft degrees to the position of the piston in the cylinder when the spark occurs.

a valve arrangement in most modern engines where the valve is positioned above the piston (in the cylinder head). The engine can be either an OHC (overhead cam) or pushrod type.

commonly referred to as a pump, the impeller is the rear halt ot the torque converter shell that drives the turbine; a driving nember in a turbine or pump.

one twelfth of a foot pound.

a device which receives metered fuel under relatively low pressure and is activated either electrically or mechanically to spray the fuel under relatively high pressure into the engine.

valve guides that are pressed fit in the cylinder head

distance from the valve spring seat to the underside of the valve spring retainer.

distance from the valve spring seat to the stem tip.

works by a negative coefficient thermistor that loses resistance as its temperature goes up (like the engine coolant temperature sensor). When the computer applies its 5-volt reference signal to the sensor, this voltage is reduced through a ground circuit by an amount corresponding to the temperature of the intake air.

a part with runners that connect the fuel system to the intake valve ports.

the passage or opening in a cylinder head that is closed by the intake valve.

the first stroke of a 4-stroke cycle engine in which the intake valve is open and the exhaust valve is closed, during which the downward motion of the piston draws the fuel/air mixture into the cylinder.

also called inlet valve, it closes off the intake port and opens it at the correct time in response to movement from the cam lobe.

valve guides that are part of the cylinder head.

valve seats that are part of the head.

a component on some turbocharged engines used to cool the compressed intake air.

engine that converts the energy contained in the fuel inside the engine into motion. Combustion engines use the pressure created by the expansion of the gases to do mechanical work.

precisely-sized, calibrated hole in a hollow passage through which fuel or air can pass.

the bearing surface on a shaft.

small locks that hold the valve retainer onto the valve stem. Also called split locks.

a sensor used in the engine control system that detects preignition, detonation and knocking. It contains a piezoelectric crystal that produces an AC voltage under vibration.

the process of fitltng one surface to another by rubbing them together with an abrasive material between the two surfaces.

a device for adjusting valve lash or maintaining zero lash in certain types of OHC engines. The lash adjuster is stationary in the cylinder head, with one end of a cam follower mounted on top of it. The other end of the follower acts on the valve stem when the camshaft lobe, which is positioned over the center of the follower, pushes the follower down.

the amount of clearance between components in a geartrain or valvetrain.

a lean burn engine is designed to operate with a very lean air-fuel ratio during light load conditions. Most modern gasoline engines are controlled to run at a chemically correct (stoichiometric) air fuel ratio (about 14.7:1) to make the three-way catalyst operate at high efficiency, reducing tailpipe emissions. Lean burn engines mix more air with the fuel when full power is not needed, resulting in better fuel economy. Air/fuel ratio in lean burn engines can be as high as 20:1. When full power is needed, such as during acceleration or hill climbing, a lean burn engine reverts to a stoichiometric (14.7:1) ratio or richer.

the holes in an engine block that the litters fit into.

the valvetrain part that rides on the camshaft lobe.

a metric measurement used to calculate the volume displacement of an engine. One liter is equal to 1,000 cubic centimeters or 61 cubic inches.

the eccentric part of the camshaft that moves the lifter.

the tab on a bearing back that fits into the slot in the main or rod bearing bore to locate it properly.

85% methanol and 15% unleaded gasoline by volume, used as a motor fuel in FFVs.

see 'mass airflow sensor'.

the lower removable lower halves of the main bearing bores.

the clearance between the main bearing journal and its bearings.

the central, load-bearing points along the axis of a crankshaft, where the main bearings support the shaft in the block.

the housings that are machined for main bearings.

the plain bearings that support the crankshaft in the engine block.

a sensor that measures changes in intake manifold pressure resulting from changes in engine load and speed. The pressure in the intake manifold as referenced to a perfect vacuum. Manifold vacuum is the difference between MAP and atmosphere pressure. For example, in a standard atmosphere (sea level) the pressure is 29.92 inches of mercury, 101 kilopascals, or 0 inches of vacuum.

measure of the degree of vacuum or pressure within an intake manifold.

relatively low pressure in an engine's intake manifold just below the throttle plate(s). Manifold vacuum is highest at idle and drops during acceleration.

see 'manifold absolute pressure sensor'.

a sensor in a fuel injection system that measures the mass (weight/density) of the incoming air flowing through a meter. The measurement transmitted to the PCM is usually either a frequency or a voltage.

failure of an explosion to occur in one or more cylinders whiIe the engine is running; can be continuous or intermittent failure.

a lack of power observed in one or more cylinders, either regularly or intermittently.

a fuel injection system in which there is one fuel injector for each cylinder.

chemically-modified oil that has been tested for viscosity at cold and hot temperatures.

lifters with contact faces that are wider than the lifter bore. They must be installed through the bottom of the lifter bores, before the cam is installed.

a folding over of the metal at the tip of the valve stem in response to pounding from too loose a valve adjustment or a defective hydraulic lifter.

a by-product of the combustion process when using petroleum-based fuels; one of the primary causes of acid rain and a contributor to global warming.

overhead cam engine. An engine with the camshaft located in the cylinder head.

the difference between the inside bearing diameter and the journal's diameter.

a line that supplies oil to areas of the engine block or cylinder head.

a groove machined in the bearing surface that provides a channel for oil flow.

the part that encloses the crankcase at the lower end of the block.

the pressure that results from resistance to flow from the oil pump. As the pump turns faster, it produces more flow. A relief valve limits the amount of pressure it can produce.

the screen that filters and keeps debris out of the oil pump.

the pump that circulates lubricating oil throughout the engine, usually driven by the camshaft (by way of the distributor).

the bottom ring on the pistons, scrapes excess oil from the cylinder walls to keep it from entering and burning in the combustion chamber.

a diagnostic software system in the ECM or PCM that monitors computer inputs, outputs, and resultant engine/transmission operations for failure. OBD-l is thought of as any of the systems in use before OBD-ll , typically 1979 to 1995 systems, although some OEMs started transitioning to OBD-ll in 1994 and 1995. OBD-ll has been a federally mandated system since 1996, it monitors emission control systems for degradation as well as for failures.

system in which the air/fuel mixture is preset by design with no feedback correction signal to optimize fuel metering.

an instrument that displays electrical activity in the form of line patterns on a screen.

the dimension by which a machined hole is larger than the standard size.

an engine with the camshaft located in the cylinder head.

an I-head engine. The intake and exhaust valves are located in the cylinder head.

regulated air pollutants, primarily NO and NO2 but including other substances in minute concentrations. Under the high pressure and temperature conditions in an engine, nitrogen and oxygen atoms in the air react to form various Nox. Like hydrocarbons, Nox are precursors to the formation of smog. They also contribute to the formation of acid rain.

a sensor that consists of a ceramic zirconium thimble, coated on each side with a very thin film of platinum. Once it reaches operating temperature of 600°F, the oxygen sensor begins to function as a very low current battery, producing between 0 and 1.0 volt with the output corresponding to the difference in oxygen between the exhaust and the ambient air. The signal from the oxygen sensor enables the computer to keep the air/fuel mixture as close as possible to the stoichiometric mixture. Under normal conditions, the oxygen sensor signal should fluctuate above and below 450 millivolts several times a second while the system is in closed loop.

diesel vehicle emission control device that traps and incinerates diesel particulate emissions after they are exhausted from the engine but before they are expelled into the atmosphere.

see 'positive crankcase ventilation system'.

a part of the positive crankcase ventilation system. Meters crankcase vapors into the intake manifold.

the part of the piston that is above the rings.

see 'wrist pin',

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.

a noise that result from excessive piston to cylinder wall clearance.

the cylindrical component that is attached to the connecting rod and moves up and down in the cylinder bore. The top of the piston forms the bottom of the combustion chamber. When combustion occurs, the piston is forced downward in the cylinder, moving the connecting rod which in turn rotates the crankshaft.

a diesel exhaust treatment system that uses a small amount of electricity from the engine to generate a nonthermal plasma (NTP) on a ceramic surface. The resulting reaction can reduce Nox and particulates by up to 90% without onboard chemicals or heating.

a plastic material that is compressed between a bearing and journal, and the resulting compressed material measured to determine the clearance.

port fuel injection (used spark-ignition engines) have injectors in the intake port near the valve. During the intake stroke, fuel sprayed into the port enters the combustion chamber along with the air charge.

a fuel injection system that uses one injector at each cylinder, making fuel distribution exactly equal among all the cylinders.

valve openings in a cylinder head.

a system that controls crankcase emissions by using a valve to meter crankcase vapors nto the intake manifold.

the third stroke of a four-stroke cycle engine which begins with the combustion of the fuel/air mixture, driving the piston away from top dead center, which then exerts turning force on the crankshaft.

a diesel engine design with a small combustion chamber in the cylinder head that contains the fuel injector. The fuel is ignited in this chamber. This design is often used with automotive diesels because of lower combustion pressures and because fuel quality is not as critical.

also called ping, it is abnormal combustion of the air/fuel mixture before it is time to do so. A hot surface or carbon deposit in the combustion chamber ignites the air/fuel mixture before the spark plug is fired. The sound of preignition can be heard as the cylinder walls vibrate. Detonation is sometimes confused with preignition.

the low-voltage circuit of an ignition system.

a paste used to determine the contact area between two parts, such as the height of the valve seat on the valve face.

the octane as posted on retail gasoline dispensers as (R+M)/2; same as Antiknock Index.

a rod between the lifter and rocker arm. They are sometimes hollow to allow oil distribution to the valves.

a device that seals the radiator and maintains a set pressure in the cooling system.

the part of the cooling system that acts as a heat exchanger, transferring heat to atmosphere. It consists of a core and holding tanks connected to the cooling system by hoses.

a seal that fits around the rear of the crankshaft to prevent oil leaks.

an up and down or back and forth motion.

a tool used to remove the ridge from the top of a cylinder bore.

a raised area at the top of a cylinder bore created by ring lear. The ridge occurs because the piston ring does not travel all the way to the top of the bore, thereby leaving an unused portion of cylinder bore above the limit of ring travel. This ridge will usually be more pronounced on high mileage engines.

a hone that removes metal and imparts a precise finish and crosshatch to the bore.

the clearance between the ends of a piston ring when installed in the cylinder bore.

a tool used to trim the ends of a piston ring to bring the ring end gap within specification.

the raised parts between the piston ring grooves.

a pivot lever mounted on a round shaft or a stud. One end of the rocker arm is applied by the push rod and the other end acts upon the valve stem.

a round pipe that is mounted parallel on top of the cylinder head. All of the rocker arms on the head are mounted on it.

a stud that is pressed or threaded into a cylinder head on which the rocker arm is mounted.

Information from the ECM, PCM ,or VCM that is displayed on the scan tool. This data includes component and system values on the data stream, DTCs, and on some systems, freeze frame data, system monitors and readiness monitors.

a surface (Usually machined) upon which another part rests or seats (e.g., valve seat).

a fuel injection system that uses one electronically pulsed fuel injector for each cylinder. The injectors are pulsed in firing-order sequence, ordinarily during the engine's intake stroke for that cylinder.

a flat, ribbed drive belt that makes multiple angles, driving several components.

when oil is not changed often enough, moisture and by products of combustion combine in the engine oil to form sludge.

engine noise caused by abnormal, uncontrolled combustion due to preignition or detonation.

an electrical device that is connected to a high voltage source. The high voltage travels down an electrode inside the spark plug and arcs across an air gap, thereby creating the spark that starts the combustion process in the combustion chamber.

an internal combustion engine in which the fuel mixture is ignited electrically. A spark-ignition engine runs on an Otto cycle - most gasoline engines run on a modified Otto cycle. This cycle uses a homogeneous air-fuel mixture that is combined before it enters the combustion chamber. Once in the combustion chamber, the mixture is compressed, then ignited by a spark plug (spark ignition). The engine is controlled by limiting the amount of air allowed inside through the use of a throttling valve placed on the air intake (carburetor or throttle body).

chemically correct. An air/fuel mixture is considered stoichiometric when it is neither too rich nor too lean; an ideal mixture is composed of 14.7 parts air to one part fuel.

the distance the piston moves from TDC to BDC.

a compressor, mechanically driven by the engine's crankshaft, that pumps air into the intake manifold.

a swirling of the air/fuel mixture in a corkscrew pattern that improves combustion.

EPA-regulated vehicle exhaust emissions released through the vehicle tailpipe. Tailpipe emissions do not include evaporative and refueling emissions, which are also regulated by EPA. EPA publishes allowable emission levels and vehicle certification standards in the Code of Federal Regulations.

see 'top dead center'.

an octane enhancer. One gram of lead increases the octane of one gallon of gasoline about 6 numbers. The EPA has phased down the use of lead in gasoline as it has been determined to be a health hazard. Lead has been prohibited in highway vehicle gasoline since January 1, 1996.

a catalytic converter system that reduces exhaust gas emission levels. Usually consists of two beds of catalyst, the upstream bed (reduction bed) reducing Nox emissions to nitrogen and oxygen and the downstream bed (oxidation bed) reducing HC and CO emissions to CO2, 02, and H2O.

also called central fuel injection, it has an intake manifold like that used with a carburetor. One or more fuel injectors are mounted in the throttle body, which resembles a carburetor in physical appearance.

a potentiometer that is mechanically connected to the throttle shaft of the throttle body assembly. It provides an input to the vehicle computer control system regarding throttle position. The TP sensor reduces the 5-volt reference voltage supplied by the computer to an amount corresponding to the degree to which the driver is holding the throttle open by foot.

in an automatic transmission, line pressure that passes through the valley of the throttle pressure spool valve.

a toothed reinforced belt used to drive the camshaft from a sprocket on the crankshaft.

a chain that drives the camshaft from a sprocket on thecrankshatt.

gears that drive the camshaft from the crankshaft.

refers in crankshaft degrees to the position of the piston in the cylinder. When referring to camshaft timing, it is when the valves open. When referring to ignition timing, it is when the spark occurs.

the position of the crankshaft for a specific cylinder when the piston is at the highest point in its vertical travel on the compression stroke.

the turning force produced by an engine.

head bolts that are often not reusable. They are torqued into yield, which means that they have purposely stretched beyond the point where they will return to their original length. This provides more uniform clamping force.

see 'throttle position sensor'.

machine for generating rotary mechanical power from the energy in a stream of fluid. The energy, originally in the form of head or pressure energy, is converted to velocity energy by passing through a system of stationary andmoving blades in the turbine.

an exhaust driven pump which compresses intake air and forces it into the combustion chambers at higher than atmospheric pressure. The increased air pressure allows more fuel to be burned and results in increased horsepower being produced.

valve guide seals that fit tightly on the valve stem. They move up and down with the valve stem acting like an umbrella to shield oil away.

a distributor mounted mechanism that controls spark advance in response to engine vacuum.

an enclosure fastened to the top of a cylinder head, over the valvetrain.

the length of time, in degrees of crankshaft rotation, that a valve is open.

the area of the valve that contacts the valve seat.

when valves remain open, usually at high rpm, due to weak or broken valve springs.

a method of refinishing the inside of a valve guide by restoring its original size. This method can be used on guides worn less than 0.007-in.

a thin bronze bushing installed in a valve guide to restore it to original size.

a bore in the cylinder head that the valve stem fits into.

small locks that hold the valve retainer onto the valve stem. Also called split locks.

the amount of clearance in the valvetrain when the lifter is on the base circle of the camshaft lobe.

the distance from the valve seat when the valve is fully open.

a small cylinder that fits into a bore above the cam lobe. It acts on a push rod and rocker arm to open the valve.

a part found at the end of some valve springs that rotates the valve each time it opens. This aids in providing even cooling to the valve.

a seal located over the valve stem, used to prevent oil from leaking down the valve guide and into the combustion chamber.

the machined surface that the valve face seats against.

a tool used to compress the valve spring on a cylinder head. When the valve spring is compressed, the valve keepers can be removed, then the spring is released and the spring, valve spring retainer and valve can be removed from the cylinder head.

the specified distance between the machined spring seat on the cylinder head to the underside of the valve spring retainer. Both grinding the valve and grinding the valve seat result in an increase in this dimension. A shim can be installed under the spring to restore the original installed height for proper spring tension.

the part that connects the valve spring to the valve and holds the valve against the cylinder head. It is held to the valve by keepers.

metal shims used, usually on aluminum cylinder heads, to protect the head from the bottom of the valve spring.

a small coil spring used to keep the valve closed against the valve seat.

the part of the valve that is inside the valve guide.

set rotations of the camshaft and crankshaft to open/close valves at proper intervals during the piston strokes for optimal operation of an engine.

the dynamic relationship between the rocker arm and valve stem during the time when the valve is opening and closing.

parts that convert camshaft movement to valve movement. These include the camshaft, cam timing parts, lifters or cam followers, push rods, rocker arms, valve and spring.

a vehicle that has the capacity of burning any combination of gasoline and an alternative fuel. Also known as a flexible-fuel vehicle.

variable valve timing allows the point at which an engine's valves open and close to change with operating conditions - such as engine speed and throttle position. In addition to changing the valve timing with respect to the crankshaft, some systems also change the duration the valve is open and the extent to which it opens. Varying these parameters allows the engine to operate more efficiently at all engine speeds while maintaining driveability.

see 'harmonic balancer'.

a valve used to limit the boost developed in a turbocharger. A wastegate allows some of an engine's exhaust flow to bypass the turbocharger's turbine under certain conditions.

also called a cooling jacket, it is the hollow area of a casting designed for coolant flow.

a sleeve, which when installed in a cylinder block, is exposed to coolant.

a hollow metal tube that secures the piston to the connecting rod and allows the piston to swivel on the rod. Also called a piston pin.