Definitions

Term	Description	Extended Description	Electrical hookup
AFPR	Adjustable Fuel Pressure Regulator	A fuel pressure regulator is needed as fuel injector flow is directly proportional to fuel pressure. Most regulators also feature a vacuum control that lowers fuel pressure at idle, when less fuel is needed.
ECT	Engine Coolant Temperature	A sensor that reports coolant temperature. Used to sense low coolant temperature (cold start) in order to enrich the mixture. Also used to control coolant fans.	Sensor is a thermistor. Hooks up with 2 wires. ECM measure the resistance. Higher temperature = Lower resistance.
ECM	Electronic Control Module	The main computer running the Fuel Injection System.	Lots and lots of wires...
EST	Electronic Spark Control	Older term used for the 7-pin HEI module that allows a ECM to control timing advance.	In the case of a GM EST distributor, the hookup is over a 4-pin connector.
HEI	High Energy Ignition	Common GM distributor introduced in 1975. EST added in 1981 (1980 for California). Coil located in cap 1975-1986. A remote coil was used from 1987-on.
IAC	Idle Air Control	A stepper motor that controls a pintle. The pintle fits in a air passge that connect above and below the throttle plates. As the IAC steps out, the pintle clears more of the passage, and airflow increase. When more air goes past the throttle plate, engine rpm increases. The IAC lets the ECM control idle speed to a preset value.	4 wires.
IAT	Intake Air Temperature. Also known as MAT, Manifold Air Temperature.	A sensor that reports the air temperature in the intake manifold. Used to adjust fuel mixture as cold air contains more oxygen than warm air and thus requires more fuel.	Sensor is a Thermistor. Hooks up with 2 wires. ECM measure the resistance. Higher temperature = Lower resistance.
MAF System	Mass Air Flow	A type of Fuel Injection System that measures the actual mass of the air entering the engine. This allows more precise engine mangement compared to a Speed Density system. However, the MAF sensor could be a air flow restriction and it is difficult to incorporate in a top-fed system, as the sensor has to be located at some distance from the throttle plates to avoid turbulence at the sensor.
MAF (sensor)	Mass Air Flow	A sensor reporting the actual mass of the air entering the engine. Not used in a Speed Density system.	The sensor consists of a thin wire that is exposed to incoming air. A current is sent through the wire heating it up. As the temperature increases, resistance decreases. The MAF sensor will increase the current until a pre-defined voltage drop is observed. The incoming air cools the wire, increasing resistance and the voltage drop. The MAF sensor will increase current until the pre-defined voltage drop is once again observed. By measuring the current required to obtain the wanted voltage drop, the mass of the air can be calculated. Output to the ECM is usually in the form of a frequency. Higher frequence corresponds to higher airflow.
MAP	Manifold Absolute Pressure	Measures the air pressure in the manifold. Think of it as a vacuum gauge. Used so that the ECM can sense the engine load and adjust both fuel and spark accordingly.	Sensor has 3 wires. Ground, Reference voltage and output voltage.
MAT	Manifold Air Temperature. See IAT.
PCM	Powertrain Control Module	Newer term replacing ECM. Usually referring to a on-board control system that controls functions besides the engine such as an automatic transmission.
SD	Speed Density	Type of Fuel Injection control. Speed density systems base the fuel and timing requirments on sensor inputs such as TPS, MAP, IAT etc, but do not measure the actual mass of air entering the engine like a Mass Air Flow System does.
TPS	Throttle Position Sensor	Current throttle position. Used to sense sudden throttle movement so that additional fuel can be added. Similar to an accelerator pump on a carburetor.	Sensor is a potentiometer. 3 wires. Ground, reference voltage and output.The output is a voltage dependent on throttle position.