Cranking Enrichment

Cranking Enrichment

During cranking when the engine speed is below a preset threshold speed of approximately 400 rev/min the ECM increases the injector pulse width to aid starting. The amount of increase varies dependant upon coolant temperature. To prevent flooding the cranking pulses are intermittent (30 pulses on, 16 pulses off).

After Start Enrichment

Additional enrichment is provided following cranking at all temperatures. The amount of additional fuel supplied is controlled by the ECM and will decay at a rate depending upon coolant temperature.

To implement after start enrichment, the ECM increases the injector pulse width.

Acceleration enrichment When the throttle pedal is depressed, the ECM receives a rising voltage from the throttle position sensor on the Y/G wire and detects a rise in manifold absolute pressure. The ECM provides additional fuel by increasing the normal injector pulse width and also provides a small number of additional pulses on rapid throttle openings.

Over-run Fuel Cut-off

The ECM implements over-run fuel cut-off when the engine speed is above 1600 rev/min with engine at normal operating temperature and the throttle position sensor in the closed position, i.e. the vehicle is ’coasting’ with the throttle pedal released. The ECM indexes the idle air control valve open slightly to increase the air flow through the engine to maintain a constant manifold depression, keeping emissions low.

Fuel is immediately reinstated if the throttle is opened. If the engine speed drops below 1600 rev/min on over-run, fuel is progressively reinstated.