Thread: 2003 GTP P 0300 multiple misfire code

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  1. #1 2003 GTP P 0300 multiple misfire code 
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    This code started popping up lately when accelerating from 30 mph and above when you push it and get into boost.

    CEL will flash if you stay on it and sometimes set and then clear itself after a few starts.

    When you do go into boost it pegs to full boost (on dash, but does not feel like full boost) and then dances around before dropping to 3 or 4 blocks.

    Drives fine under light load.

    I am going to replace the fuel filter which seems like it has never been changed. And i have been avoiding because the nut is so rusted on i am sure i will break the fuel line off getting it off, so i got a repair kit coming ahead of time.

    It has 229000 mi. I have owned it since 199000 mi. Checked plugs when i bought it and they looked ok (guessed 40000 on them). So plugs and wires will be second step.

    The wild boost gauge is making me think there may be another issue, but no P0033 code for boost control solenoid. So will wait on that.

    New MAF not to long ago. Cat did not rattle last time i checked and no smell.

    Any other thoughts?


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  3. #2 Re: 2003 GTP P 0300 multiple misfire code 
    GrandPrix Junkie
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    Maybe a failing ICM?
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  4. #3 Re: 2003 GTP P 0300 multiple misfire code 
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    Changed the plugs and wires last night. OEM stuff and it seems a little better but i can still make the CEL flash and pending P0300 code.

    I will change the fuel filter tomorrow after the fuel line fix kit come today.

    To me thats all preventative stuff so if the fuel filter does not fix it then i may need some ideas on what to do next before throwing parts at it. I took a look at all the vac lines and no obvious leaks.

    Never a specific cylinder misfire code. Always random misfire P0300 code.



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  5. #4 Re: 2003 GTP P 0300 multiple misfire code 
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    Fuel filter surgery done. Take her for a run after i clean up.

    Looks like the rear brake lines will be toast soon. Ah minnesota salt.


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  6. #5 Re: 2003 GTP P 0300 multiple misfire code 
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    Still random misfires under boost. No rattle in cat or smell. Vacuum lines look good.

    That about taps the preventative stuff. I can do before tossing some parts at it. Maybe can do a crank relearn on tuesday.

    Threw a different boost control solenoid on that i had and and still no help.

    Could all 3 coils be going at once?

    If i ever get 2 of my GPs together i could swap a ICM and see if that helps.

    Other thoughts?


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  7. #6 Re: 2003 GTP P 0300 multiple misfire code 
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    Bad tank of gas?


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  8. #7 Re: 2003 GTP P 0300 multiple misfire code 
    GTX Level Member bandook's Avatar
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    I have seen where one coil went bad, and it caused the other 2 to malfunction. I'll see if i can find it if I remember what YouTube channel i saw it on. Maybe ScannerDanner.
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  9. #8 Re: 2003 GTP P 0300 multiple misfire code 
    GrandPrix Junkie
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    I had 1 coil crack on my GT and it ended up taking the ICM with it for some reason.
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  10. #9 Re: 2003 GTP P 0300 multiple misfire code 
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    Got some coil packs coming today ind an ICM tomorrow to swap in and see if that fixes it.

    Seems to drive better and miss less when the engine bay is cool but once it gets up to temp stumbles under load pretty consistently.

    Thanks for the replies.


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  11. #10 Re: 2003 GTP P 0300 multiple misfire code 
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    Put it on a tech 2 and it was the 1/4 coil pack misfiring badly under load.

    So back to full power.

    Seems like the OBD2 code could have steered me there with more than just the random misfire code. It was pretty consistent

    .


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