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Thread: LT1 pcm won't flash anymore.

  1. #1
    Fuel Injected! babywag's Avatar
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    LT1 pcm won't flash anymore.

    This is on a 1994 Caprice wagon.
    I wanted to make some minor changes and have never had or seen this issue before.
    I've flashed it problem free many times using EEHACK.

    It gives an error stating something about VPP voltage, that the power will need to be removed from pcm to clear flash code.
    So I disconnected the battery for a while and tried again. Same error message.
    Lather rinse repeat, but this time rebooted the laptop as well.
    No dice, same error, are the flash chips done? Anything else I can try?
    Tony
    Looking to buy TunerCat OBDII
    '88 Jeep Grand Wagoneer (aka Babywag) and '90 Jeep Grand Wagoneer (aka JUNKbucket) both fuel injected
    '94 Caprice Wagon

  2. #2
    Fuel Injected!
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    It sounds like you need more battery voltage, or have a poor connection between the battery and the PCM.

  3. #3
    Fuel Injected! babywag's Avatar
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    Quote Originally Posted by lionelhutz View Post
    It sounds like you need more battery voltage, or have a poor connection between the battery and the PCM.
    No VPP voltage is used as the means to reflash the chip. It applies voltage to certain pins which allows erase/reflash.

    Car still operates normally, just cannot reflash due to this error that keeps coming up.
    Tony
    Looking to buy TunerCat OBDII
    '88 Jeep Grand Wagoneer (aka Babywag) and '90 Jeep Grand Wagoneer (aka JUNKbucket) both fuel injected
    '94 Caprice Wagon

  4. #4
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    Vpp voltage is used to erase the chip and is applied internaly on the board via software switch. EEhack send a special command to pcm to do it and if the response is not as expected it might give an error. I think I got this error once or twice but can`t remember anything about it. Can you make a verbose log.
    The vpp voltage must be solid 12v for the chip to get errased.

  5. #5
    Fuel Injected! babywag's Avatar
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    Quote Originally Posted by kur4o View Post
    Vpp voltage is used to erase the chip and is applied internaly on the board via software switch. EEhack send a special command to pcm to do it and if the response is not as expected it might give an error. I think I got this error once or twice but can`t remember anything about it. Can you make a verbose log.
    The vpp voltage must be solid 12v for the chip to get errased.
    I'll try. I put in spare pcm and it flashed fine. I'll try to duplicate error on the bench w/ one that refused to flash.
    I have a feeling the flash chip(s) are possibly the cause?
    Tony
    Looking to buy TunerCat OBDII
    '88 Jeep Grand Wagoneer (aka Babywag) and '90 Jeep Grand Wagoneer (aka JUNKbucket) both fuel injected
    '94 Caprice Wagon

  6. #6
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    They are good for 100 000 erase/program cycles, according to Intel specs.

    You can try reading the pcm also. If it reads fine, check the bin for corruption.

  7. #7

  8. #8
    Fuel Injected! babywag's Avatar
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    Quote Originally Posted by lionelhutz View Post
    It sounds like you need more battery voltage, or have a poor connection between the battery and the PCM.
    So let's give this man a prize!!

    Yesterday I started thinking about this and decided to check things out.
    It led me to discover something.
    Turns out the aftermarket alarm was robbing the main ignition feed off the ignition switch.
    Like well over 1volt, and wild fluctuations between 11.1 to 12.6 volts looking @ pcm voltage datastream with engine running.
    The alarm installer did a good job, but for whatever reason the main alarm module was killing voltage.

    All 4 fuses in underhood fuse block read low ~12v-12.5v(checked @diff. times) with car running. Every other fuse ~14v.
    Key on engine off even lower obviously.

    Today I bypassed the alarm splice, and now getting rock solid 13.6v @ 4 fuses and watching pcm datastream.

    So big thx to lionelhutz, betting there is nothing wrong with pcm and was as he suggested.

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