Computers and Control Systems: Description and Operation

PGM-FI System Description:

PURPOSE
These vehicles are equipped with a Programmed Fuel Injection ELECTRONIC CONTROL MODULE (ECM) which is located at the passenger side footwell under the carpet. The ECM controls all phases of engine operation. In order to accomplish this control, the ECM relies on the input from a variety of engine operation sensors.

OPERATION
The ECM compares input signals with those stored in memory to determine what steps should be taken to achieve maximum performance, fuel economy, and meet emission standards. The ECM outputs the necessary signals to the fuel system, ignition system, air control system, and the emission control systems.

The ECM also records any malfunctions in the monitored systems. When a malfunction is detected, the ECM will insert a pre-programmed value to substitute for the defective signal, flash the Check Engine light, and store the malfunction in erasable memory as a numeric code.

Additionally, should the ECM itself fail, there is a back-up circuit which will control the fuel system to allow the vehicle to continue functioning (Back-up Mode).