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Someone swaped my PCM for a later model now car wont run

This is a discussion on Someone swaped my PCM for a later model now car wont run within the Computer & Tuning forums, part of the LSx Technical Help Section category; I have a 1998 Trans am, I had the transmission rebuilt and it works fine but when the mech ran ...

  1. #1
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    1998 trans am

    Someone swaped my PCM for a later model now car wont run

    I have a 1998 Trans am, I had the transmission rebuilt and it works fine but when the mech ran a diagnostic on the computer it was sending the wrong info to the transmission so he was afraid the PCM was bad and might burn out the transmission so I went to this other guy who claims all he does is build fbodies he swaped out my PCM for a 99 PCM and the car would not start the fuel pump was nor coming on so he put my PCM back in and it still didn't work so I bought a new fuel pump and it didn't come on then I jumped the pump from the fuse box, the pump came on but the car didn't start so I checked the fuel rail and there was no fuel in the rail now what should I do from here.

  2. #2
    Your friendly policeman FinZ28's Avatar
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    I'm thinking you need a PCM from a '98 model, although I could be wrong. Or it may need to be programmed for your car, at least.

    Did some reading and it looks as though you'll have to repin your PCM, as the harnesses are different. I still believe you'll have to have the new PCM programmed to your VIN. As for why your fuel pump won't work as it should, I'm not sure where to start there.
    Last edited by FinZ28; 05-06-2012 at 02:15 PM.
    2001 Chevy Camaro Z28 A4
    SLP cold air intake/lid, SLP smooth bellow, Pacesetter LT's, ORY, Magnaflow exhaust, BMR STB, adjustable Panhard rod, SFC's, LCA's, 1LE sway bars, cross-drilled rotors

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    '98 PCM's are different than later model PCM's -- they are not interchangeable. What exactly was the stock PCM doing wrong in his opinion?

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    Spaz is My Mentor SMWS6TA's Avatar
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    Sounds like you need to talk with Frost. He is a member and one of our sponsors. He does tuning on our cars for a living and he should be able to help you.

    You can reach him via PM or through his website located in the sponsor section.

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    1998 trans am

    It was giving to wrong info to the transmission I just got rebuilt so me and the mech. Who rebuilt it were wondering if the PCM would eventually burn the transmission out

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    I tried talking to frost at first and he said he never heard of a PCM acting like that and he didn't carry my year PCM, so i don't know if I should send it to him because if it's bad then he probably can't tune it

  7. #7
    Your friendly policeman FinZ28's Avatar
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    Was your car throwing any codes prior to the PCM swap?

    If you've ever considered a mail-order tune, I'd send your '98 PCM to Frost and let him take a look at it. If all is well, he should be able to tune your PCM without any trouble. If the PCM is truly going bad then you can either repin the '99 PCM and get it reprogrammed to your VIN, or sell the '99 PCM and pick up a good '98 PCM.
    Last edited by FinZ28; 05-06-2012 at 04:06 PM.

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    Senior Member cpop98ws6's Avatar
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    Check your PCM fuse.

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    ʢ ൧ ൨ ൩ ൪ ൫ ൬ ൭ ൮Ր Ց Ւ Փ Smittro's Avatar
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    Quote Originally Posted by bvar20 View Post
    It was giving to wrong info to the transmission I just got rebuilt so me and the mech. Who rebuilt it were wondering if the PCM would eventually burn the transmission out
    ??? Never heard of such a thing..

    As a rebuilder he/they should know that.

    PAJeff is correct.

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    Where is the PCM fuse located

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    Senior Member cpop98ws6's Avatar
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    Under the hood fuse box, the one closest to the radiator. Should tell you on the lid which fuse it is, im pretty sure is a 15amp fuse.

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    Senior Member cpop98ws6's Avatar
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    If the fuse is bad, change it and plug in your 98' PCM and you should have fuel pressure again.

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    Veteran 0rion's Avatar
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    what a mess.......you need to take the car to a certified mechanic. You have a lot going on with that car. You've also spent A LOT of money that you didn't really need to spend most likely. PCM sending bad information to the tranny makes zero sense to me......it sounds like something a mechanic would tell you that doesn't know shit. I just really think at this point it would be in your best interest to find a reputable mechanic that can handle this job. You've gotten a couple mechanics so far that have cost you money, time, and work that weren't necessary.

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    ʢ ൧ ൨ ൩ ൪ ൫ ൬ ൭ ൮Ր Ց Ւ Փ Smittro's Avatar
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    Quote Originally Posted by 0rion View Post
    what a mess.......you need to take the car to a certified mechanic. You have a lot going on with that car. You've also spent A LOT of money that you didn't really need to spend most likely. PCM sending bad information to the tranny makes zero sense to me......it sounds like something a mechanic would tell you that doesn't know shit. I just really think at this point it would be in your best interest to find a reputable mechanic that can handle this job. You've gotten a couple mechanics so far that have cost you money, time, and work that weren't necessary.
    This.....

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    Actually Orion the transmission mech. Did a great job rebuilding the transmission and he showed me what the diagnostic was in person before and after the rebuild and showed me on a print out what the readings should be he was only alerting me that I may have a bad computer. My mistake was trusting this second guy that I was sent to that is more of a parts changer than a mech. If learned that he's only built cars with all the parts in place never has he fixed a real problem. I need to find someone in my area who can look at my PCM and troubleshoot it, I tried the local dealerships but they tell me the the car is too old they can't check the pcm

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    Do you still have your '98 PCM, or did the parts changer chuck it? As far as sending bad info, the only thing I can equate that to is if you had a bad sensor, such as the throttle position sensor, then I could understand your transmission having issues as the shift tables and such are based off input it receives from the TPS, MAP, engine RPM and so forth.

  17. #17
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    Well those sensors were check because like I said it was giving this bad info before the rebuild and the sensors check out good but he still replaced them with new one anyway and it still had the same problem. And yes I still have the 98 PCM it was put back in my car I told to keep his computer

  18. #18
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    what were the symptoms of the car prior to having it worked on? Also, in order for that 99 pcm to work ( and it will work) you have to repin it. Do you know if it was repinned at all? That may be why your 98 pcm isn't working now. Did you have a security light on or flashing? Have you checked your fuel pump relay?

    Good luck and keep the thread updated....we'll try to help as much as possible but with something like this is always much easier if you have the car in front of you. I would want to make sure your pinned correctly for your 98 pcm first and then start trouble shooting the fueling issue like you normally would.

  19. #19
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    The car was running and the transmission was shifting I had just got the tranny rebuilt the problem was when the mech at the transmission shop put his scanner on the car the tfp switch assembly data showing up wrong

  20. #20
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    And no I don't know if the plug was repinned it had a 98 PCM in it and like I said it was running fine other than the bad readings

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