Computers and Control Systems: Description and Operation

Engine Coolant Temperature Sensor
The engine temperature sensor is located in the flow of the engine coolant and sends information concerning temperature to the ECM.

Oxygen Sensor
The exhaust oxygen sensor is located in the exhaust system and monitors oxygen content in the exhaust gas stream. The ECM receives this information and adjusts the air/fuel ratio as necessary.

Manifold Absolute Pressure Sensor
The manifold absolute pressure (MAP) sensor measures changes in the intake manifold pressure resulting from engine load and speed changes. As the pressure changes, the electrical resistance of the sensor changes. This change in resistance causes a voltage change which is amplified and sent to the ECM.

Vehicle Speed Sensor
The vehicle speed sensor (VSS) is located behind the speedometer in the instrument cluster. The sensor sends a series of pulses to the ECM used to determine road speed. The ECM uses this information to reset the idle air control motor, canister purge and [1][2]torque converter clutch. Do not drive vehicle without VSS, as idle quality may be affected.

Throttle Position Sensor
The throttle position sensor (TPS) is connected to the throttle shaft and is controlled by the throttle mechanism. The TPS converts the throttle valve angle to an electrical signal and transmits the signal to the ECM.

Hall Effect Unit
The Hall Effect Unit is located above the pickup coil in the distributor and sends engine RPM information to the ECM. This unit is used in place of the ``R'' terminal of the conventional HEI module.

Park/Neutral Switch
The park/neutral switch indicates to the ECM when the transmission is in park or neutral. Do not drive vehicle with park/neutral switch disconnected, as idle quality may be affected in park or neutral.

A/C Compressor Clutch Engagement
The A/C compressor clutch engagement signal tells the ECM that the A/C compressor clutch is engaged.





Manifold Air Temperature (MAT) Sensor, 1987-88
The Manifold Air Temperature (MAT) sensor is a thermistor, or resistor that changes its value based on temperature. The MAT sensor is mounted on the engine air cleaner on 4-121 overhead cam engines, on the TBI air bonnet on 4-121 overhead valve engines, and on the intake manifold on 4-151 engines. Low air temperatures produce a high resistance while high temperatures produce low resistance. The ECM supplies a 5 volt signal to the MAT sensor, through a resistor in the ECM and monitors the voltage. The voltage will be high when the air is cold and low when the air is hot. By monitoring the voltage, the ECM calculates the air temperature and adjusts fuel and spark advance.

Ignition Module, 1987-88
The ignition module, used on 4-121 overhead cam engines, receives a signal from the pickup coil which is sent to the ECM as a reference signal. The ECM uses this reference signal for RPM and spark calculation.

Crankshaft Sensor, 1987-88
The crankshaft sensor sends a signal through the ``DIS'' (Direct Ignition System) module to the ECM. The ECM uses this reference signal to calculate RPM and crankshaft position.