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Need help with P0300 misfire

This is a discussion on Need help with P0300 misfire within the Computer & Tuning forums, part of the LSx Technical Help Section category; In coming home two weeks ago (200 mile trip),, the SES light come on and the engine started to run ...

  1. #1
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    red
    1999 Camaro SS

    Need help with P0300 misfire

    In coming home two weeks ago (200 mile trip),, the SES light come on and the engine started to run a little rough.

    I limped the car home and check for DTC codes. I had multiple misfires and mainly on #3. The misfire history on #3 was in the many thousands.

    I pulled some plugs and found that they were very sootie black. Pull one O2 and it was in bad shape, also. The LFTFs were +25%. I judged that the O2 were reading lean when it really was not. I had turned the PCM to -5% LTFT in most FTCs. So I figured that if I installed new front O2 sensors and all new plugs, clear the DTC codes, the engine would be back all good with no misfires.

    But that did not happen, I still had a noticable miss, as well as, ATAP telling me random misfires on #3.

    So I swapped #1 coil with #3, cleared codes, no change, still have misfire #3.

    Now, I swapped #1 plug wire for #3 plug wire, cleared codes, still #3 misfires.

    So whats going on??? Can the PCM identify the wrong cylinder? maybe its a misfire on #6 for example.

    In addition, some searching turned up a CKP Learn procedure, what is this thing?

  2. #2
    Senior Member SeVeReDiStOrTiOn's Avatar
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    05 Wrangler
    00 Z28 sold :-(

    might be a bad injector...is it leaking fuel?

  3. #3
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    1999 Camaro SS

    I'll have to check the fuel pressure drop off at key off. But I am thinking that for the LTFTs to go to +25%, the PCM must have detected a lean condition in order to increase the LTFTs to max. Therefore, a clogged injector might do this.

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