Air Mass Meters

An instrument which measures both engine intake air mass and factors which affect air density, such as temperature, humidity, and pressure.


Alternators are used in modern automobiles to charge the battery and to power a car’s electric system when its engine is running. Alternators have the great advantage over direct-current generators of not using a commutator, which makes them simpler, lighter, less costly, and more rugged than a DC generator. The stronger construction of automotive alternators allows them to use a smaller pulley so as to turn faster than a DC generator, improving output when the engine is idling. The availability of low-cost solid-state diodes from about 1960 onward allowed car manufacturers to substitute alternators for DC generators. Automotive alternators use a set of rectifiers (diode bridge) to convert AC to DC. To provide direct current with low ripple, automotive alternators have a three-phase winding.

Auxiliary Air Valves

The auxiliary air valve typically serves the same purpose as the high idle cam serves on an engine with a carburetor: it raises the idle so the engine will not stall when cold. Usually this unit consists of a thermal bulb that pushes a piston up a cylinder against a spring. A port is located in the side of this cylinder which allows air into the engine; as the engine warms up, the thermal bulb pushes the piston farther up, covering the port and so bringing the idle back down to a slower “warm idle”.


Automotive starter batteries (usually of lead-acid type) provide a nominal 12-volt potential difference by connecting six galvanic cells in series.

Each cell provides 2.1 volts for a total of 12.6 volt at full charge. Lead-acid batteries are made up of plates of lead and separate plates of lead dioxide, which are submerged into an electrolyte solution of about 35% sulfuric acid and 65% water. This causes a chemical reaction that releases electrons, allowing them to flow through conductors to produce electricity. As the battery discharges, the acid of the electrolyte reacts with the materials of the plates, changing their surface to lead sulfate.

When the battery is recharged, the chemical reaction is reversed: the lead sulfate reforms into lead oxide and lead. With the plates restored to their original condition, the process may now be repeated.


A small metal cylinder which is usually located in the distributor. It is installed between the breaker points and coil to prevent arcing at the breaker points by absorbing or storing the excess current. A condenser (also called a capacitor) has the ability to absorb and retain surges of electricity. It is constructed of two metal plates separated by an Insulator.

Contact Sets

Two or more metal terminals, located inside the distributor on vehicles with non-electronic ignitions. These terminals are brought into contact and then separated by the movement of the cam wheel on the rotating distributor shaft. The points regulate the intensity and duration of the current that is conducted to each spark plug by interrupting the flow of current from the coil as they open and close. Also called Contact points, Breaker points, or ignition points.

Crank Sensors

A crank sensor is a component used in an internal combustion engine to monitor the position or rotational speed of the crankshaft. This information is used by engine management systems to control ignition system timing and other engine parameters. Before electronic crank sensors were available, the distributor would have to be manually adjusted to a timing mark on the engine.

The crank sensor can be used in combination with a similar camshaft position sensor to monitor the relationship between the pistons and valves in the engine, which is particularly important in engines with variable valve timing. It is also commonly the primary source for the measurement of engine speed in revolutions per minute.

Crank sensors in engines usually consist of magnets and an inductive coil, or they may be based on magnetically triggered Hall effect semiconductor devices. Common mounting locations include the main crank pulley, the flywheel, and occasionally on the crankshaft itself. This sensor is the most important sensor in modern day engines. When it fails, there is a small chance the engine will start (engine will likely cut out after a few minutes of driving) but it mostly will not start

Distributor Caps

An insulated cover containing a central terminal or tower with a series (one per cylinder) of terminals or towers that are evenly spaced in a circular pattern around the central terminal or tower, the secondary voltage travels to the central terminal or tower where it is then channeled to one of the outer terminals or towers by the Rotor. The cap also keeps dirt and moisture out of the Distributor.

Ignition Coils

A pulse Transformer which is a part of the Ignition system. It receives a small amount of electrical Voltage from the Battery and steps up the low primary voltage and amplifies it into a big jolt of voltage of about 20,000 volts, and sends it to the Spark plugs via the Distributor. It is made of two windings and a Core of iron. The primary coil has about 200 turns of relatively heavy wire. The secondary windings may have as much as 22,000 windings of fine wire. As electricity travels through the Primary winding, it produces a Magnetic field in the coil. When the points open, the magnetic field collapses and the movement of the magnetic field induces Current in the secondary windings of the coil. The voltage is stepped up in proportion to the ratio of secondary to primary turns and the Distributor directs this high voltage to the Spark plug. Also called just coil.

Ignition Lead Sets

A set of leads which deliver an electrical charge from the distributor to the spark plugs.

Ignition Modules

A transistorized component in an electronic ignition that triggers the ignition coil to fire high voltage. It replaced the breaker points on older cars.

MAP Sensors

A manifold absolute pressure sensor (MAP) is one of the sensors used in a (usually fuel injected) internal combustion engine’s electronic control system. The MAP sensor provides instantaneous manifold pressure information to the engine’s electronic control unit (ECU), which is needed to calculate air density and determine the engine’s air mass flow rate. This in turn determines the required fuel metering for optimum combustion.

Oil Pressure Sensors

A sensor mounted above the oil filter that supplies information on the engine oil pressure to the corresponding warning light

Radiator Fan Switches

A switch which works in conjunction with the water temperature sensor to regulate the water temperature in the radiator.

Reverse Light Switches

Reverse light switches are usually mounted on the front of the gearbox and activate when reverse gear is selected, sending a signal to the reverse lights in rear ligth cluster.

Rotor Arms

A small rotating cap-like unit at the end of the distributor shaft. It is located on the Breaker cam inside the cap. It connects between the center Electrode and the various outer Spark plug terminals as it turns, thus distributing the high Voltage from the Ignition coil secondary winding to the proper Spark plug.


The thermostat is a small device, usually around 2 inches in diameter, which sits between the engine and the radiator.

Its job is to block the flow of coolant to the radiator until the engine has warmed up – only when the engine reaches its operating temperature (generally about 200 degrees F, 95 degrees C)does the thermostat open. By letting the engine warm up as quickly as possible, the thermostat reduces engine wear, deposits and emissions.

Throttle Position Sensors

A potentiometric fuel injection switch with two contacts for the two end positions of the throttle valve, which sends a signal to the electronic control unit when the throttle valve is closed (idle) or wide open (full load). The sensor wiper position is proportional to throttle position. The computer uses this information to control fuel flow