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cylinder misfire

This is a discussion on cylinder misfire within the Internal Engine forums, part of the LSx Technical Help Section category; recently had code indicating cyl. #5 misfire. since my 99 bird has 150K miles i assumed new coil packs plugs ...

  1. #1
    Junior Member
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    blk
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    cylinder misfire

    recently had code indicating cyl. #5 misfire. since my 99 bird has 150K miles i assumed new coil packs plugs wires would solve problem. didnt!!! im an aircraft mechanic, so i do have someskills, but i dont have a garage right now. a auto mech. friend took a look and thought it might be a busted valve spring. do i pay a mechanic to open her up and know for sure, or since its high milage i was considering new heads. if i do upgrade my heads, whats a good bolt-on pkg? i do plan on keeping car and when i get into new house doing complete restore. any comments welcomed.
    thanks

  2. #2
    Senior Member rajiv1998's Avatar
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    1998 Pontiac Trans Am

    If had a code that said "Cylinder 6 miss fire" and it turned out to be a busted spark plug wire. When I was replacing the plugs, I forgot to reinstall the metal boot that came off the stock plug wire. The new MSD wires were actually rubbing on the exhaust manifold and burned over time. Car kept on suring and missfire.

    I wouldnt think its a busted spring or anything with the valvetrain. You will most likley hear noises if its a valvetrain problem. Take off the valve covers and make sure your springs are ok.
    "Life is to short to drive a slow car"

    Gone but not forgoten: 1998 Pontiac Trans Am M6 "The Black Bandit"
    Bought- 11-18-05
    Sold- 10-14-08

  3. #3
    The Demon Demon_Z28's Avatar
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    usually a broken wire will cause a noise and arcing to occur. I'd swap a coil with another to see if the misfire transfers to another cylinder. But you said you replaced them, so my next thing to tell you if it isn't your plug/ plug wire/ or coil pack. It could be your Fuel Injector. The last thing to check after a bad fuel injector would be to do a compression and leak down test on CYL. #6. If it happens to be a dead cylinder or bad compression, it could be piston rings or it could be a head issue.

    Busted Spring would cause some major issues and noise and engine performance issues.
    Last edited by Demon_Z28; 12-03-2010 at 01:44 PM.

  4. #4
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    turns out to be broken push rod!! guess valve stuck and snap. rocker and spring seem fine. replaced rod, cleared code, running great!!!
    thanks

  5. #5
    The Demon Demon_Z28's Avatar
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    Glad you figured it out! now that you found one broken push rod, did you roll test them aqll to see if they are bent. It could reduce engine performance. If anything I'd get some hardened pushrods. $100 can save you in the long run. I run TSP ChromeMolly Hardened Pushrods. 7.400 length (Stock length). Good Luck.
    Last edited by Demon_Z28; 12-04-2010 at 12:59 PM.

  6. #6
    The Bandit Wesman's Avatar
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    1998 Trans Am WS6

    Quote Originally Posted by Demon_Z28 View Post
    Glad you figured it out! now that you found one broken push rod, did you roll test them aqll to see if they are bent. It could reduce engine performance. If anything I'd get some hardened pushrods. $100 can save you in the long run. I run TSP ChromeMolly Hardened Pushrods. 7.400 length (Stock length). Good Luck.
    Same here. I had a few that were bent just from high RPM shifts. Aftermarket hardened push rods are much stronger than the factory ones.

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