Idle Air Fuel Ratio

Idle Air Fuel Ratio

During idle conditions the ECM implements an idle air fuel ratio map. The ECM implements this map when the engine speed is below an idle speed set point.

NOTE: The idle CO is adjustable via the serial port using TestBook.

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 reduce at a rate depending upon coolant temperature. To implement after start enrichment, the ECM increases the injector pulse width.

Acceleration enrichment During acceleration, additional fuel is required to ensure response is smooth. This enrichment is applied by the ECM, which receives an output voltage (rising) from the TP sensor and a rise in manifold absolute pressure. This additional fuel is provided by increasing the injector pulse width and instigating additional pulses at 80°crank intervals.

Over-run Fuel Cut-off

Over-run fuel cut-off is implemented by the ECM when the following conditions exist:

• Coolant temperature is above 80°C approx.
• Engine speed above approximately 2200 rev/min.