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Thread: Pcm Question

  1. #1
    93sevillests is offline Cadillac Owners Member
    Automobile(s): seville sts
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    Pcm Question

    I have a 1993 cadillac sts with the 4.6 and I am wondering if there is a sure way to find out if the pcm needs to be replaced right now
    I dont have any codes showing up on the dash
    however when I got the car I had a few i took it to the mech and he fixed them
    and he told me I would need to get a new fuel rail, injectors,pcm
    i am already out a grip load of cash for the rail and the injectors plus the other ends in outs that the mech fixed


    any advice would be helpful
    Thanks for your help


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  3. #2
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: Pcm Question

    If you feel that the engine is just not running correctly, there's a better chance that the ICM (Ignition Control Module) under the coils, not the PCM (Powertrain Control Module) is the culprit. You need to run ACDelco Platinum plugs, #41-950, and ACDelco wires. Clean the coil connectors for both plug wires and primary 12V and signal wiring. Check the wiring against the diagrams. It makes a big difference. Google "waste spark ignition" for insight. You may have one or more weak coils - there are 4.

  4. #3
    N0DIH's Avatar
    N0DIH is offline Cadillac Owners Master
    Automobile(s): 94 Fleetwood Brougham
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    Re: Pcm Question

    The L67 3800 (supercharged NOT the non SC!) coils are a hotter coil. You can get take offs from Sinister Drag Designs in Chicago or Morad Auto who specializes in 3800's.

    Get GM coils not aftermarket. Used are fine, ohm them out to be sure they are good.

    Quote Originally Posted by submariner409 View Post
    If you feel that the engine is just not running correctly, there's a better chance that the ICM (Ignition Control Module) under the coils, not the PCM (Powertrain Control Module) is the culprit. You need to run ACDelco Platinum plugs, #41-950, and ACDelco wires. Clean the coil connectors for both plug wires and primary 12V and signal wiring. Check the wiring against the diagrams. It makes a big difference. Google "waste spark ignition" for insight. You may have one or more weak coils - there are 4.

  5. #4
    ewill3rd is offline Cadillac Technician
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    Re: Pcm Question

    Why do you think there is a problem with the computer?
    I see some information but what is the problem you are after?

  6. #5
    N0DIH's Avatar
    N0DIH is offline Cadillac Owners Master
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    Re: Pcm Question

    What he said.... Sorry wasn't paying close attention!

    But I have said it a lot before, don't throw parts at it, that only serves to make one broke or just plain frustated. Troubleshooting it takes time and learning or finding someone who does know.

    Why would he say rails, injectors and PCM, are they all bad? Which ONE is bad? How did he determine it? It urks me when mechs sell people on the 3-4 things their car had bad on it when only one is. Maybe they need it, but the customer needs to know that too.

    If "injectors" are bad, which one, not all surely are bad. If one is bad, then it will miss. And pulling injectors wires one at a time will show the cyl that is not firing, not necessarily if the injector or the coil is bad.

    If a COIL is bad you will find 2 cyls bad, if an injector, one.

    So pull injectors wires off one at a time with the engine running and note rpm drop. when you get to a cyl or 2 with no drop, paydirt.

    Disconnect the IAC so the PCM won't compensate for the idle drop.

    Reconnect all when done.

    I ohm out coils, primary and secondary and have never had an issue with not finding a good/bad one.


    Quote Originally Posted by ewill3rd View Post
    Why do you think there is a problem with the computer?
    I see some information but what is the problem you are after?


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