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I Ideal Air/Fuel Ratio A term used for Stoichiometric air/fuel ratio. Ignition The firing of a spark plug to ignite the air/fuel mixture in the combustion chamber.
Ignition Circuit An ignition circuit is made up of two sub-circuits: the primary, which carries low voltage; and the secondary, which carries high voltage. The primary circuit is controlled by the ignition key. It releases 12 volts of electricity from the battery or alternator through the coil to a set of breaker points in the lower part of the distributor, or to the relay in electronic ignition applications. When the points or relay are closed, current flows through the chassis back to the battery, completing the circuit. When the points or relay are open, the flow stops, causing a high-voltage surge to pass from the coil through a rotor in the top of the distributor to the spark plugs. Once the car has started, the voltage regulator protects the battery from being overcharged by the alternator. part of the low -voltage current is absorbed by the condenser when the points are open. 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 Switch A five-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 ACCESSORIES, LOCK, and OFF. Ignition System The various components that provide the spark to ignite the air and fuel mixture in an engine during the combustion process. Some late-model engines (and virtually all vintage engines) use a distributor to tell the coil when to fire. Many late-model vehicles feature a distributorless ignition system, in which case the engine management computer tells the coil when to fire. The spark energy then passes through the spark plug wires to the spark plugs. Many people enhance the performance of an ignition system by adding an ignition box and a high-performance coil, or even swapping to higher-performance spark plugs. Ignition Temperature The lowest temperature at which a combustible material will ignite and continue to burn independent of the heat source. Ignition Timing The moment at which the spark plug fires, usually expressed in the number of crankshaft degrees before the piston reaches the top of its stroke. Ignition Wire See spark plug wire. Independent Front Suspension Abbreviated IFS. A type of front suspension system in which each wheel can move independently of the other. This improves driver control on rough terrain, and it also allows automotive engineers to create a vehicle with better handling and a more comfortable ride. There are several styles of IFS, including designs that use coil springs and designs that feature torsion bars. Independent Rear Suspension Abbreviated IRS. A type of rear suspension system in which each wheel and tire operate independently of the other for better traction in tough conditions. This design also reduces body roll, as well as a vehicle's tendency to squat down in the rear when accelerating or leaning forward when braking. By keeping the vehicle's weight better balanced, IRS improves both ride quality and handling--and safety. Very few vehicles come with IRS (Corvettes and Jaguars are among those that do), but it is possible to retrofit IRS to some cars and trucks. Independent Suspension Suspension in which each wheel is sprung individually so that any disturbance on the wheel has no effect on the opposite wheel.
Induction
System
Inline Engine An engine having the cylinders in a straight line, one after the other. Also called a "straight" engine. Intake Stroke The first stroke is called the intake stroke. The piston moves down the cylinder, creating a partial vacuum in the cylinder. A mixture of air and fuel is then forced through the inlet valve into the cylinder by atmospheric pressure, now greater than the pressure in the cylinder. The exhaust valve stays closed during the stroke.
Intake Valve A valve in a cylinder head that opens to allow air and fuel into a combustion chamber. Part of a vehicle's valvetrain. Internal-Combustion Engine Any engine, either reciprocating or rotary, in which the fuel is consumed in the interior of the engine rather than outside of the engine.
J
THE
MOST COMMON JACKS
Jackshaft A shaft found in most overhead cam engines that is used to drive the distributor, fuel pump, and oil pump.
K Knock A noise within an engine generally caused by detonation or preignition. Knock-Off A single wing nut for fastening a wheel to the hub. Easily removed and replaced, it is struck (knocked off) with a mallet on the wings. Knock Sensor The knock sensor senses when fuel is burning unevenly and causing "knocking" or irregular vibrations in the engine. It consists of an electric coil that is wound around two ceramic rods with a magnet in the center. The vibration of the engine causes the rods to vibrate. This disturbs the coil's magnetic field and alters the current passing through the coil. This disturbance returns to the computer as a signal pattern that the computer analyzes. The computer then determines whether the vibrations are characteristic of engine knocking.
L Leaf Springs A number of slightly curved, flexible steel plates of varying lengths, mounted one atop the other. The ends are attached to the chassis, and the middle is fixed to the axle. Also called semi-elliptic springs. Lifter Body The valve lifter body houses the valve lifter mechanism. The valve lifter is the unit that makes contact with the valve stem and the camshaft. It rides on the camshaft. When the cam lobes push it upwards, it opens the valve. Lift Kit A kit designed to increase the space between a vehicle's suspension and its frame, or between its body and its frame. A lift kit makes it possible to fit larger wheels and tires under the vehicle, for increased ground clearance and suspension travel. A lift kit might include blocks, add-a-leafs, new leaf springs, coil spring spacers, lifted spindles, replacement control arms and special brackets to mount suspension components lower on a frame.
Lighting Circuit The automobile lighting circuit includes the wiring harness, all the lights, and the various switches that control their use. The complete circuit of the modern passenger car can be broken down into individual circuits, each having one or more lights and switches. In each separate circuit, the lights are connected in parallel, and the controlling switch is in series between the group of lights and the fuse box. The parking lights, are connected in parallel and controlled by a single switch. In some installations, one switch controls the connection to the fuse box, while a selector switch determines which of two circuits is energized. The headlights, with their upper and lower beams, are an example of this type of switch. Again, in some cases, such as the courtesy lights, several switches may be connected in parallel so that any switch may be used to turn on the lights.
The limiting coil passes the current from the battery to the common connection of two coils at the lower terminal on the dash unit. This current may pass from either the operating coil of the dash unit and the other over to the tank sending unit. When the fuel tank is low or empty, the sliding brush cuts out all resistance in the tank unit. Then the current will passes through the tank unit circuit because of the low resistance, and only a small portion will pass through the operating coil to the dash unit. This coil is not magnetized enough to move the dash unit pointer, which is then held at the "Empty" position by the limiting coil. When the tank is full or partly full, the float of the tank unit will rise to the surface of the fuel and move the sliding brush over the rheostat, putting resistance in the tank unit circuit. This results in more current will then passing through the operating coil to give a magnetic pull on the pointer, which overcomes some of the pull of the limiting coil. When the tank is full, the tank unit circuit contains the maximum resistance to the flow of the current. The operating coil will then receive its maximum current and exert pull of the pointer to give a "Full" reading. As the tank empties, the operating coil loses some of its magnetic pull and the limiting coil will still have about the same pull so that the pointer is pulled toward the lower reading. Live Axle An axle that transmits power either by separate half shafts or by side chains, as opposed to a dead axle. Load Sensing Proportioning Valve (LSPV) A brake hydraulic system control valve that works like a proportioning valve, but also takes into consideration the amount of weight carried by the rear axle. Locknut A nut used to lock an adjustment nut, or other threaded component, in place. For example, a locknut is employed to keep the adjusting nut on the rocker arm in position. Lockwasher A form of washer designed to prevent an attaching nut from working loose. Louver A slatted air intake or air outlet. Slats used to capture and control the air flow. Low-Profile Tire A tire with a short sidewall. Tires with an aspect ratio of 55 or lower are considered low profile. This type of tire improves handling, but also produces a noticeable increase in ride firmness and tire noise. Many people also swap to low-profile tires because they look sportier, since they commonly are found on sports cars and exotics.
Lug
M Main Bearings The main bearing secure the crankshaft in its place. The largest number of main bearings a crankshaft can have is one more than the number of cylinders, but it can have one less bearing than the number of cylinders. Not only do the bearings support the crankshaft, but one bearing must control the forward-backward movement of the crankshaft. This bearing rubs against a ground surface of the main journal, and is called the "thrust bearing." Maintenance-Free Battery A sealed battery having no practical provision for the addition of water to the cells, since periodic maintenance is unnecessary.
MAP sensor See manifold absolute pressure sensor.
Master Cylinder Controls the brake fluid, acting as a reservoir when you are not applying the brakes. Mopar A contraction of "motor parts" that has become a slang term for Chrysler vehicles, especially those from the musclecar era. Chrysler's performance parts division is called Mopar Performance. Mud Tire A tire with a special tread pattern that is designed to provide traction in mud. A mud tire typically will feature large tread blocks, wide grooves and larger-than-average channels along the edge of the tire, so it can shed mud, water, gravel and other debris.
Multimeter An electrical test instrument with the capability to measure voltage, current and resistance.
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