Fuel Quantity: Function

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To be able to calculate the amount of fuel to be injected into each cylinder, the ECM needs to determine the amount of air mass drawn into each cylinder. To perform this calculation, the ECM processes information from the following sensors:

Mass air flow (MAF) sensor.
Crank speed and position (CKP) sensor.
Engine coolant temperature (ECT) sensor.
Throttle position (TP) sensor.

During one engine revolution, 4 of the 8 cylinders draw in air. The ECM uses CKP sensor information to determine that one engine revolution has taken place, and the MAF sensor information to determine how much air has been drawn into engine. The amount of air drawn into each cylinder is therefore 1/4 of the total amount measured by the ECM via the MAF sensor.

The ECM refers the measured air mass against a fuel quantity map in its memory and then supplies an earth path to the relevant fuel injector for a period corresponding to the exact amount of fuel to be injected into the lower inlet manifold. This fuel quantity is in direct relation to the air mass drawn into each cylinder to provide the optimum ratio.

During adaptive fuelling conditions, information from the heated oxygen sensors (HO2S) is used by the ECM to correct the fuel quantity to keep the air/fuel ratio as close to the stoichiometric ideal as possible.