The Engine Computer is by far the least likely suspect but that's what a lot of mechanics jump on first because they're used to seeing an extremely high failure rate on GM vehicles. If you measure that voltage at the injectors, I'll bet you find it missing there too.
The most common failure item is the camshaft position sensor. Next would be the crankshaft position sensor. Both of them have to supply signals to the Engine Computer. When they do, the computer turns on the relay to send voltage to the coil pack, injectors, oxygen sensor heater, and fuel pump or pump relay.
If you measure the voltage feeding the coil pack with a test light, you should see it light up for one second after turning on the ignition switch. That proves the relay and wiring are okay and the computer has control of it. If that voltage doesn't come back during cranking, suspect one of those sensors. A scanner will display a diagnostic fault code telling which signal is missing. If there's no code, one of them is shorted and killing the power supply for both of them. That will result in no signal from either sensor and the computer won't even know it should be expecting the signals.
You might get away with using a digital voltmeter to measure that voltage but many of them don't respond fast enough to show that one-second pulse of voltage.
Friday, March 23rd, 2012 AT 2:44 AM