Port Fuel Injection

The Electronic Control Module (ECM), located in the passenger compartment, is the control center for the fuel injection system. The ECM continually monitors and processes the input information and generates output commands to the various systems affecting vehicle performance.
A removable calibration unit (PROM) enables the ECM to recognize and adjust for vehicle variations (vehicle weight, axle ratio, etc.). There are specific ECM/PROM combinations for each specific vehicle which are not interchangeable.
A CALPAK is also installed in the ECM. The CALPAK allows fuel delivery if other parts of the ECM are damaged.
On 1987-88 4-122 (2.0L), V6-173 (2.8L) and V8 engines and 1988 V6-231 (3800) engine, the PROM, CALPAK and ESC control module are combined into a single calibration unit called MEM-CAL. The MEM-CAL includes calibrations for the specific engine/vehicle calibration, as well as the back-up fuel control circuitry needed to allow engine operation in the event of an ECM failure.
The ECM also performs the diagnostic function of the fuel injection system. When the ECM senses an operational problem, it will illuminate the ``Check Engine'' lamp and store the appropriate code(s) to identify the problem area.