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Need some mech. help

This is a discussion on Need some mech. help within the General Help forums, part of the LSx Technical Help Section category; 2000 Trans AM WS6 80k had car scanned came back with multiple cylinder misfires. Car had a bad idle, popping ...

  1. #1
    clebouef04
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    Need some mech. help

    2000 Trans AM WS6 80k

    had car scanned came back with multiple cylinder misfires. Car had a bad idle, popping exhaust with a rich smell, and nearly no power, along with a blinking SES light. I changed plugs, wires, and the fuel filter myself. When I pulled the #1 plug I found some gunk in the gap of the plug. I bought it down to a local mechanic. It was then diagnosed by him and he came up with a bad ignition coil pack along with a weak one on cylinders #1 & #7. I had him replace both of those. It didn't help the situation any. He then did a leak test on my valves thinking it was an exhaust valve but couldn't make them leak. Next he did a compression check on all cylinders and found those 2 cylinders with he said about 20 psi. This mechanic said his knowledge of the LS1 wasn't that great and he didnt do that kind of overhaul work. I then picked the car up and made some calls to a knowledgable mechanic shop and was told it could be a fuel problem due to that motor being port injected but to bring my car in. I need some opinions before I bring it in for maybe a very expensive overhaul. With these problems note the car is not burning oil noticeably. Could it sensor related or more serious like head gaskets, or ring damage. Any help would be greatly appreciated.

  2. #2
    Grand Imperial Wizard Sarge's Avatar
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    Many things come to mind.....oxygen sensors going south will do this sometimes....are you throwing a code?

  3. #3
    Kill Whore LS1What's Avatar
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    The 20 psi on 2 cylinders, I don't like the sound of that. You checked the oil already I take it, no milkshake in the oil pan is always great. Check your coolant tank and radiator for nasty black coolant. Could have popped a headgasket between a water jacket and two cylinders. That is assuming the ones with low compression are adjacent to each other.(Won't cause heating problems either) I hope this isn't the case, but no sensor is gonna trick out a compression reading. You can't ignite an atomized air/fuel mix with no compression, could be where the miss is coming from. Though, it could be the exhaust valves as he mentioned also. Do you know the actual compression numbers for each cylinder by any chance??
    Last edited by LS1What; 11-24-2005 at 05:50 PM.

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    G2 LS1 SEAN's Avatar
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    We'll be back... GatorSS's Avatar
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    The compression loss makes me think it could be burnt valves.

  6. #6
    Senior Member SeVeReDiStOrTiOn's Avatar
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    Wierd how the low compression cylinders are the first and last cylinder in the driver side...change your oil and check it for coolant. Could be a blown headgasket.. cracked/warped head...having any over heating issues?

  7. #7
    clebouef04
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    Oil looks good from what I can tell. I'll change it to get a better look at it. Cars not running hot or consuming radiator fluid. Out of town until Thurs. but I'll check those things first. Also I'm not sure what the compression readings were on the good cylinders. Thanks for the help guys. So no fuel restriction problem could cause any of this then?

  8. #8
    Veteran Hi-Po's Avatar
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    Blinking SES light means your cat is going out!!

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    Senior Member SeVeReDiStOrTiOn's Avatar
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    Quote Originally Posted by Hi-Po
    Blinking SES light means your cat is going out!!
    Blinking ses is actually a misfire bro....p0420/p0430 are the cat codes.

  10. #10
    Senior Member SeVeReDiStOrTiOn's Avatar
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    Quote Originally Posted by clebouef04
    Oil looks good from what I can tell. I'll change it to get a better look at it. Cars not running hot or consuming radiator fluid. Out of town until Thurs. but I'll check those things first. Also I'm not sure what the compression readings were on the good cylinders. Thanks for the help guys. So no fuel restriction problem could cause any of this then?
    No..lack of fuel wouldn't lower compression in the cylinders. Bad rings, headgasket, warped head...etc will though. Lack of fuel can cause a misfire though...but your compression needs to be fixed first, then see if you still have the misses.

  11. #11
    99PontTA
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    look for broken or cracked valve springs

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    My guess is its something in the head or having to do with the head cause of the combination of bad compression and misfire. I would remove the head and have it checked to see if its warped and check for cracks or something, also wouldnt hurt to replace the bolts and gasket while your in there.

    That brings me to another idea... Has the head ever been off the car? The head bolts must be replaced for proper torque on them when they are put back in, so if the head was off and the bolts werent replaced that would cause some problems. Also, cylinders 1 and 7 are first and last on drivers side, the 2 and olny 2 short bolts of the 10 main head bolts are the first and last of the middle set, maybe that has something to do with it.

    Dunno just throwing out ideas there.

    Good luck
    -Scott

  13. #13
    Kill Whore LS1What's Avatar
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    Quote Originally Posted by sk8runeg
    My guess is its something in the head or having to do with the head cause of the combination of bad compression and misfire. I would remove the head and have it checked to see if its warped and check for cracks or something, also wouldnt hurt to replace the bolts and gasket while your in there.

    Good luck
    -Scott
    Could be both, but low compression can/will cause a misfire..

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