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Fuel Injector (Multi Point)

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Fuel Injector (Multi Point) Waveform Notes

The injector is an electromechanical device which is fed by a 12 volt supply. The voltage will only be present when the engine is cranking or running, due to the voltage supply being controlled by a tachometric relay.
The length of time the injector is held open will depend on the input signals seen by the Electronic Control Module (ECM) from its various engine sensors.

The held open time or ‘injector duration’ will vary to compensate for cold engine starting and warm-up periods. The duration time will also expand under acceleration. The injector will have a constant voltage supply while the engine is running and the earth path will be switched via the ECM, the result can be seen in the example waveform. When the earth is removed a voltage is induced into the injector and a spike approaching 50 volts is recorded.

Multi-point injection may be either sequential or simultaneous. A simultaneous system will fire all 4 injectors at the same time with each cylinder receiving 2 injection pulses per cycle (720° crankshaft rotation). A sequential system will receiving just 1 injection pulse per cycle, this is timed to coincide with the opening of the inlet valve.

As a very rough guide the injector duration for an engine at normal operating temperature, at idle speed are:-

  • 2.5 ms - Simultaneous
  • 3.5 ms - Sequential