Question about 1994 Oldsmobile 88

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No injector pulse width if system voltage over 12.5 volts

I work a a Gm dealer and pretty good at what I do, But this one has me stumped as well as others in the shop. The car is an 89 Pontiac Grand Am 2.5 with TBI. heres what it came in for and where we are now. It came in with a no start. when you crank it and keeped the key in start it would run. if you let go it would die. after running some diag. we did notice that there was no pulse wisth after starting it, there would be spark but the pulse wisth would go away. after a day of diag. i unplugged the alternator and it continued to run. pulse width was back, if you put a shop charger on it, the same thing, it would loss pulse width, seams anything over a system voltage of 12.5 would kill the injector pulse. the ecm and prom where replaced. its not the injector driver, we have even used another know good ecm and got the same results. the ignition module as well as the crank sensor have been replaced as well. all engine ground and grounds the pcm are good and solid. all power have been verified as well. any help would be appriciated. I was told just to give it back to the customer, but i dont like to give up.

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  • support754 Dec 02, 2008

    with the alternator disconnected, if i apply a battery charger to the battery, once it goes past 12.5v i lose the pulse from the injector, the ground/driver sie, i still have power.

  • support754 Dec 02, 2008

    ignition switch is new, and im not lossing any powers anywhere in the system, as well as at the ecm.

  • support754 Dec 02, 2008

    i lose the ground/driver side, voltage is stable. with aternator disconnected and a charger on the vehicle, once system voltage hits 12.5 i lose the injector ground/driver circuit.

  • support754 Dec 02, 2008

    ignition switch is new, and i have all powers and grounds verified.

  • SM124 May 11, 2010

    Do you lose the injector feed or the ground side. Have you checked for a bad diode in the alternator putting out an a/c signal that could cause the pcm to misread the signal from the module.

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Hi, it sounds to me that you are losing contact at the ignigtion switch..C1...

Posted on Dec 02, 2008

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