Fuel Quantity

The ECM controls engine fuel quantity by providing sequential injection to the cylinders. Sequential injection allows each injector to deliver fuel to the cylinders in the required tiring order.

To achieve optimum fuel quantity under all driving conditions, the ECM provides an adaptive fuel strategy.

Conditions
Adaptive fuel strategy must be maintained under all throttle positions except:
^ Cold starting.
^ Hot starting.
^ Wide open throttle.
^ Acceleration.

All of the throttle positions mentioned above are deemed to be 'open loop'. Open loop fuelling does not rely on information from the H02 sensors, but the air/fuel ratio is set directly by the ECM. During cold start conditions the ECM uses ECT information to allow more fuel to be injected into the cylinders to facilitate cold starting. This strategy is maintained until the H02 sensors are at working temperature and can pass exhaust gas information to the ECM. Because of the specific nature of the other functions e.g. hot starting, idle, wide open throttle, and acceleration they also require an 'open loop' strategy. For NAS vehicles with secondary air injection for cold start conditions, refer to the Emissions section.

Adaptive fuel strategy also allows for wear in the engine and components, as well as slight differences in component signals, as no two components will give exactly the same readings.

Function
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.