Thread: Misfire like no other

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  1. #1 Misfire like no other 
    GTX Level Member MTXGTP's Avatar
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    ok today i finally hooked up a scan tool to look at all my sensors and stuff and just to check on it plus i had what i beleived was a misfire well it is misfiring and its just one cyl, but it only misfires at idle. #4 is the only cyl. misfiring. well i think it might be a manifold gasket. any other ideas would be well appreciated.
    Justin Young, Kansas
    1999 silver GTP DHP pcm,3" Cattless hogan DP,Front PLOG,3.4 pulley, ported TB, ported LIM, ported supercharger housing.porting done by GBP
    coming soon: LS6 springs ,1.9rr
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  2. #2 Re: Misfire like no other 
    SS-DD Level Member IndeedSS's Avatar
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    Quote Originally Posted by MTXGTP View Post
    ok today i finally hooked up a scan tool to look at all my sensors and stuff and just to check on it plus i had what i beleived was a misfire well it is misfiring and its just one cyl, but it only misfires at idle. #4 is the only cyl. misfiring. well i think it might be a manifold gasket. any other ideas would be well appreciated.
    Plug, plug wire, coil pack?
    04 Indy SS build #972 - Traded
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  3. #3 Re: Misfire like no other 
    GTX Level Member MTXGTP's Avatar
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    nope all tested good plugs new wire is new ive tested the coil pack.
    Justin Young, Kansas
    1999 silver GTP DHP pcm,3" Cattless hogan DP,Front PLOG,3.4 pulley, ported TB, ported LIM, ported supercharger housing.porting done by GBP
    coming soon: LS6 springs ,1.9rr
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  4. #4 Re: Misfire like no other 
    SS-DD Level Member IndeedSS's Avatar
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    sure sounds electrical since it is only present at idle and only one cylinder.
    04 Indy SS build #972 - Traded
    2010 Camaro SS LS3
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  5. #5 Re: Misfire like no other 
    GTX Level Member MTXGTP's Avatar
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    ive seen it where a manifold will not seal and allow unmetered air into the cyl. causing a miss fire.
    Justin Young, Kansas
    1999 silver GTP DHP pcm,3" Cattless hogan DP,Front PLOG,3.4 pulley, ported TB, ported LIM, ported supercharger housing.porting done by GBP
    coming soon: LS6 springs ,1.9rr
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  6. #6 Re: Misfire like no other 
    SS-DD Level Member IndeedSS's Avatar
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    Quote Originally Posted by MTXGTP View Post
    ive seen it where a manifold will not seal and allow unmetered air into the cyl. causing a miss fire.
    sounds like you know what the problem is, yes?

    ok let me backup you have a leak at the exhaust manifold gasket, and that would cause a misfire? Wouldn't running open headers cause a misfire on all cylinders then?
    04 Indy SS build #972 - Traded
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  7. #7 Re: Misfire like no other 
    GTX Level Member MTXGTP's Avatar
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    no at the LIM no im not sure cause i did a coolant pressure check and found out that im losing pressure but i have no leaks externally. im wondering if coolant could cause an miss fire.
    Justin Young, Kansas
    1999 silver GTP DHP pcm,3" Cattless hogan DP,Front PLOG,3.4 pulley, ported TB, ported LIM, ported supercharger housing.porting done by GBP
    coming soon: LS6 springs ,1.9rr
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  8. #8 Re: Misfire like no other 
    GrandPrix Junkie
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    yes it can
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  9. #9 Re: Misfire like no other 
    SS-DD Level Member IndeedSS's Avatar
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    ^^^ agreed on the coolant since it can kill the spark or combustion.
    04 Indy SS build #972 - Traded
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  10. #10 Re: Misfire like no other 
    Bastard Reptile's Avatar
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    I had this problem today actually...on a local's car. A slight coolant seep was killing one cylinder. Bad gasket in his case.

    Is your plug wet from coolant?

    Test to see if you have any spark at that plug. Pull it, and then put the boot on it and hold it with some insulated pliars. Have someone crank on it while you watch for a spark.
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  11. #11 Re: Misfire like no other 
    GTX Level Member MTXGTP's Avatar
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    ok but last time i tried this i got a not so very nice shock.
    Justin Young, Kansas
    1999 silver GTP DHP pcm,3" Cattless hogan DP,Front PLOG,3.4 pulley, ported TB, ported LIM, ported supercharger housing.porting done by GBP
    coming soon: LS6 springs ,1.9rr
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  12. #12 Re: Misfire like no other 
    GTP Level Member Toasty's Avatar
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    Quote Originally Posted by MTXGTP View Post
    ok but last time i tried this i got a not so very nice shock.

    insulated pliers and a glove, man
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  13. #13 Re: Misfire like no other 
    Bastard Reptile's Avatar
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    Quote Originally Posted by MTXGTP View Post
    ok but last time i tried this i got a not so very nice shock.
    That's why I said insulated pliars.

    But if you said that you pressurized the coolant system, and it's bleeding off....you will need to find the leak. It could be going into the intake, or worse going into the block. If you think that you have it pegged at which cylinder it is, then pressurize the system again, wait for it to bleed off and check that plug. If it is going into the cylinder the plug will be soaking wet, and you have found your problem.

    New intake gaskets could be in your future.
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  14. #14 Re: Misfire like no other 
    GXP Level Member Zef_66's Avatar
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    If this much coolant was going into the cylinder and fouling the plug to where it won't spark, I would imagine it would be very difficult to start. Do you find it hard to start at all?
    2001 GSE
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  15. #15 Re: Misfire like no other 
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    I'm laying money on a plug going dead. I had the same problem were a plug just went dead all of a sudden. is the car running rich? One sure fire way to tell if your burnning coolant with the car running smell the exhaust gas's if they smell sweet then the cars burnning coolant. Keep us posted on whats going on
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  16. #16 Re: Misfire like no other 
    GTP Level Member Toasty's Avatar
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    if you're burning coolant, you also may see white smoke from the exhaust...
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  17. #17 Re: Misfire like no other 
    GrandPrix Junkie
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    but not always (I had a truck came in with a cracked head and no gasket that showed no smoke or smell)
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  18. #18 Re: Misfire like no other 
    GTX Level Member MTXGTP's Avatar
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    ok well today on the way home i started to get a miss fire during boost so plug has fouled. so would you say a intake or a head gasket if its an intake ill start on it tomorrow.
    Justin Young, Kansas
    1999 silver GTP DHP pcm,3" Cattless hogan DP,Front PLOG,3.4 pulley, ported TB, ported LIM, ported supercharger housing.porting done by GBP
    coming soon: LS6 springs ,1.9rr
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  19. #19 Re: Misfire like no other 
    SS-DD Level Member IndeedSS's Avatar
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    Quote Originally Posted by MTXGTP View Post
    ok well today on the way home i started to get a miss fire during boost so plug has fouled. so would you say a intake or a head gasket if its an intake ill start on it tomorrow.
    Don't you have to pull the LIM to get to the heads off? My vote is LIM gaskets. But that is just going by historical data.
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  20. #20 Re: Misfire like no other 
    GTX Level Member MTXGTP's Avatar
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    yea you do have to casue the LIM bolts to the heads
    Justin Young, Kansas
    1999 silver GTP DHP pcm,3" Cattless hogan DP,Front PLOG,3.4 pulley, ported TB, ported LIM, ported supercharger housing.porting done by GBP
    coming soon: LS6 springs ,1.9rr
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