Electronic Control Module

The Electronic Control Module (ECM) receives and processes information from all data sensors to produce the proper pulse duration ("on" time) for the injector(s), correct idle speed and proper spark timing. The ECM performs calculations to control the following operating conditions: engine start, engine running, fuel enrichment during acceleration, lean fuel mixture during deceleration, fuel cut-off and battery voltage correction.

During engine starts, the ECM delivers an injector pulse for each distributor reference pulse received (synchronized mode). The injector pulse width is based upon coolant temperature and throttle position. The air/fuel ratio is determined by the ECM when the throttle position is less than 80 percent open. Engine starting air/fuel ratio ranges from 1.5:1 at -33°F (-36°C) to 14.7:1 at 201°F (94°C).

If the engine is flooded, the driver must depress the accelerator pedal all the way down. At this position, the ECM calculates injector pulse width equal to an air/fuel ratio of 20:1. This air/fuel ratio will be maintained as long as the throttle valve remains wide open and engine speed is below 600 RPM. If the throttle position becomes less than 80 percent open and/or engine speed exceeds 600 RPM, the ECM changes the injector pulse width to that used during engine starting.

When the engine is running above 400 RPM, the ECM operates in the open loop mode. In open loop, the ECM calculates injector pulse width based upon coolant temperature and manifold absolute pressure. The engine will remain in open loop operation until the oxygen sensor reaches operating temperature, the coolant temperature reaches a preset temperature, and a specific period of time has elapsed after the engine starts. When all these conditions are met, the ECM operates in the closed loop mode. In closed loop, the ECM controls injector pulse width based upon oxygen sensor signals to maintain the air/fuel mixture ratio close to 14.7:1.

During deceleration, the ECM looks at changes in throttle position and manifold pressure and reduces fuel to fuel injector(s). When deceleration is sudden, the ECM can cut fuel off completely for short periods of time. When battery voltage is low, the ECM can compensate for a weak ignition system by increasing injector "on" time, increasing idle RPM, and increasing ignition dwell.

The ECM used on fuel injected vehicles has a "learning" capacity which allows it to make minor corrections to fuel system. If the battery is disconnected, the "learning" process must begin all over again. During this period, a change may be noted in vehicle performance. To "teach" the vehicle, ensure the vehicle is at normal operating temperature. The vehicle should then be driven at part throttle, moderate acceleration and idle until performance returns.