Fuel Injector Electrical Quick-Fix

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Fuel Injector Electrical Quick-Fix

Running electrical tests on the fuel injector should be a main component of an auto repair injection strategy. The fuel injector is a coil winding, that magnetically moves a fuel valve pintle. Here are the electrical facts about the fuel injector.

1) The opening and closing of the injector can be determined, by the superimposed voltage and current waveform.
2) As a rule of thumb, fuel injectors draw about 950 milli Amps, or almost 1 Amp.
3) The first step in testing a fuel injector is to make sure it's being triggered, so use a noid light to make sure ECM is doing its job. Do not use an LED test light to test injectors, as the current or Amps is all wrong to test the injector.
4) Use a stethoscope or screw driver to listen for a clicking injector noise.
5) The injector always has 12 volts steady power applied to it, through a power relay. On some vehicles, the injector relay stays off with engine off, so a crank signal is needed by the ECM to turn the injector relay on. Dodge and many European cars use this system.
6) The ECM provides a pulsed ground to activate the fuel injector.
7) At idle, most ECMs give the injector about a 3 to 5 milli second pulse. During cranking the pulse may reach over 20 milli seconds.
8) The best way to determine fuel flow pulse is not using injector pulse width, is by doing a duty cycle test with the multi-meter.
9) There are 2 electrical tests done on the fuel injector, the duty-cycle and the oscilloscope test. To run a duty-cycle test, connect the multi-meter set to duty-cycle between injector pulsed wire and 12 volt power. On 99% of vehicles, at idle, the duty-cycle should be about 2.9 to 3%.
10) To run the waveform test, use an oscilloscope of graphing meter with a good resolution. Connect the leads between battery negative and injector pulsed wire. Look for the following waveform spots. Make sure it's grounded all the way down. Look for a clean pulse-width. Make sure the shut off spike is at least 35 volts or higher. Many ECMs clip the turn-off spike at 35 volts. The high spike is an indication of injector coil winding health.

Remember to use the injector resistance specification. The 0.95 Amps rule of thumb here is just that, a general rule. That concludes the Fuel Injector Electrical Quick-Fix.

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