Fuel Injection Duration

The multi-point injector is an electro-mechanical device, which is fed by a 12 volt supply from either the fuel injection relay or from the Electronic Control Module (ECM). The injector consists of a solenoid-operated valve, which is held in the closed position by a spring until the ECM completes the earth circuit. When the electromagnetic field lifts the pintle off its seat, fuel is delivered to the engine. The total lift on the pintle is approximately 0.15 mm (6 thou) and has a reaction time around 1 millisecond.
The voltage at the injector is present only when the engine is cranking or running, because the voltage supply is controlled by a tachometric relay.
The injector is supplied with fuel from a common fuel rail. The length of time for which the injector is held open depends on the input signals seen by the engine management ECM from its various engine sensors.
These input signals will include:
· The resistance of the coolant temperature
· The output voltage from the airflow meter (when fitted)
· The resistance of the air temperature sensor
· The signal from the Manifold Absolute Pressure (MAP) sensor (when fitted)
· The position of the throttle switch / potentiometer
The held open time or injector duration varies to compensate for cold engine starting and warm-up periods, a large duration decreasing the injection time as the engine warms to operating temperature. The duration also expands under acceleration and contracts under light load conditions.


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