Non-Turbo

The Electronic Control Module (ECM) is a computer that judges air/fuel ratio as rich or lean according to oxygen sensor output voltage. Based on oxygen sensor and other input data, the ECM generates a controlling signal to the carburetor mixture control solenoid (duty solenoid), causing it to continuously cycle on and off (duty cycle). By changing the duty cycle, the ECM controls air/fuel ratio adjustments.

The ECM duty cycle control signal is selected from four operational modes:

1. Inhibit mode: Fixed control signal to duty solenoid.
2. WOT (wide open throttle) mode: Pre-programmed duty cycle generated based on engine RPM.
3. Open loop mode: Pre-programmed duty cycle generated based on various parameters (cold oxygen sensor, for example).
4. Closed loop mode: Calculated duty cycle generated based on oxygen sensor and other sensor outputs.

The ECM has a self-diagnostic capability that is monitored via a dash mounted "Check Engine" light. When the ECM detects a fault in a monitored component and/or circuit, the light will come on and stay on (while the engine is running), alerting the driver to seek service. With intermittent problems, the light may come on and then go out, but a trouble code will be stored in ECM memory if correct parameters are met. The technician can then extract trouble codes from the ECM that will aid in the performance of efficient troubleshooting and repair.

To allow one model of ECM to be used for different vehicles, a device called a programmable read only memory (PROM) is utilized. The PROM is located in the ECM and contains information on vehicle weight, engine, transmission, axle ratio, etc. Because the PROM is vehicle specific, it must be be transferred to a new ECM if the original is being replaced.

In addition, the ECM also controls various emission control components through its operation of associated vacuum switching valves and solenoids.

ECM CONNECTIONS

ECM Connector Identification: