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Misfire cyl #3 HELP!!!!

This is a discussion on Misfire cyl #3 HELP!!!! within the General Help forums, part of the LSx Technical Help Section category; I drove the vehicle last night - got on the gas - now I have a misfire. I noticed the ...

  1. #1
    Member blownh2x's Avatar
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    99 Firehawk (M6) #518

    Misfire cyl #3 HELP!!!!

    I drove the vehicle last night - got on the gas - now I have a misfire. I noticed the misfire when I was parking the car and it was idling. I'm having the misfire on cyl #3 only (P303). I drove the car to a friends house nearby and changed some parts around. still has the misfire. Then I'm driving home and the vehicle is stumbling bad and decelerating, I press the gas and the car has no power, then all of a sudden it has power and lost power again. I barely made it into my garage from the lack of power. I changed some more parts around trying to move the problem to a different cylinder, but no luck. I have no cats, so only the pre-cat 02's. Did I maybe screw up an 02 sensor or not have enough fuel pressure?

    I've checked everything below

    1. coil pack - changed with cyl #1
    2. spark plug - changed with cyl #1
    3. Compression test - ok
    4. Injector - changed with cyl #1
    5. Plug wire - checked ohm reading and changed with cyl #1
    6. Installed stock tune - no help / reinstalled custom tune
    7. Cleaned MAF sensor

    checking fuel pressure next and pulling valve cover off. any other ideas?

  2. #2
    King 0f n00bz shady milkman's Avatar
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    maybe the injector plug..clean off the plug and make sure it has slack

  3. #3
    King 0f n00bz shady milkman's Avatar
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    blacker than wesleysnipes
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    but yeah for sure take the vlave cover off and take a look.

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    Life in the Fast lane sunsetorangess's Avatar
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    Like said above, double check the injector harness and also the 02 harness.
    J
    2001 SS, Its not the car its the Driver that matters....

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    Member blownh2x's Avatar
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    99 Firehawk (M6) #518

    Quote Originally Posted by shady milkman View Post
    maybe the injector plug..clean off the plug and make sure it has slack
    I can hear the injector firing with a stethoscope, I did an ohm reading on it as well and checked it to another injector. I'm scratching my head on this one a little bit.

    I smelled a real faint burning smell last night in the garage also now that I think of it - I'll check the 02 wiring. I remember zip tying it pretty good though - thanks for the help.
    Last edited by blownh2x; 03-27-2009 at 08:42 AM.

  6. #6
    King 0f n00bz shady milkman's Avatar
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    the way you discribe it though..sounds like it would be alot more then 1 cylinder misfiring...a possible fueling issue or i also hate to say it..did you check the main injectors plug..the white one with the blue locking thing ? when i removed my intake once i forgot to plug one side in...

  7. #7
    King 0f n00bz shady milkman's Avatar
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    blacker than wesleysnipes
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    opps never mind about the injector thing..you can hear it spraying

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    Member blownh2x's Avatar
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    99 Firehawk (M6) #518

    I can unplug inj#3 and vehicle stays the same because of the misfire on that cyl. If I unplug any other inj the vehicle idle changes so I know my prob is with #3 and I also had the P303 code. I don't hear anything going on in the valve train though - at least nothing rattling or out of the ordinary.

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    King 0f n00bz shady milkman's Avatar
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    blacker than wesleysnipes
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    Quote Originally Posted by blownh2x View Post
    I can unplug inj#3 and vehicle stays the same because of the misfire on that cyl. If I unplug any other inj the vehicle idle changes so I know my prob is with #3 and I also had the P303 code. I don't hear anything going on in the valve train though - at least nothing rattling or out of the ordinary.
    weird.

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    Member blownh2x's Avatar
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    99 Firehawk (M6) #518

    Will the valve covers come off pretty easy or is it a pain in the a$$

  11. #11
    Just a souped up sunfire. Ryans99LS1's Avatar
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    They arent bad. Just take the coil rack off and then you just unbolt it.

  12. #12
    King 0f n00bz shady milkman's Avatar
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    Quote Originally Posted by blownh2x View Post
    Will the valve covers come off pretty easy or is it a pain in the a$$
    very easy.

  13. #13
    TunedbyFrost.com Tuner Frost's Avatar
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    swap entire coil packs left to right and see if it moves. If it does, since you already looked at the coil the main coil harness connector is suspect. I have definitely had issues with that before.

  14. #14
    Member blownh2x's Avatar
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    99 Firehawk (M6) #518

    Quote Originally Posted by Frost View Post
    swap entire coil packs left to right and see if it moves. If it does, since you already looked at the coil the main coil harness connector is suspect. I have definitely had issues with that before.
    I did switch coil packs on cyl#1 to cyl#3 thinking the misfire would move to cyl#1 from cyl#3. I also checked for actual spark coming out the coil pack - it was good and strong. checking valve train when I get home after work and fuel pressure

  15. #15
    Member blownh2x's Avatar
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    99 Firehawk (M6) #518

    Update

    OK, so I have a couple of bent push rods, a few rocker arms that are loose in the bearing department, and a electrical connector with some corrosion for the coil packs. I need to fix this problem and hopefully my problem above will go away. I'm thinking about going with 1.8 rocker arms and some chromemoly push rods, what do you think? Anything on sale you know of? I'm buying this weekend. Why are there different lengths of push rods? Is stock length 7.4"?

  16. #16
    Just a souped up sunfire. Ryans99LS1's Avatar
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    stick with stock rockers.. Or if you wanna good stock upgrade use ls7's. not sure on stock length of the rods though.

  17. #17
    Member blownh2x's Avatar
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    99 Firehawk (M6) #518

    Quote Originally Posted by Ryans99LS1 View Post
    stick with stock rockers.. Or if you wanna good stock upgrade use ls7's. not sure on stock length of the rods though.
    I believe the LS7's have a taller installed height. I'll probably go with LS6 valve springs

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