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Thread: Lower compression numbers after lean Dyno ugly plugs

  1. #1
    Senior Member Carroll Shelby
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    Lower compression numbers after lean Dyno ugly plugs

    Initially ran a compression test and had numbers between 185-210 with most around 200-205 so good enough for me. Went to the Dyno and above 4700 or so the air fuel would go up above 14 and buck or pop at times. Blew out the maf messed withe the restrictor and a pull without it but pretty much the same thing. Fuel pressure looked to stay around 58 which is correct for ls1.
    Pulled the plugs and a few of them have some weird deposits on them that I now think is oil-will post pics later.

    Proceeded another compression test and the numbers are down to 160-190 several cylinders down 20-30 or even 40. Tried a different gauge but same thing. Both tests all the plugs were pulled, efi fuses pulled and ignition coils unplugged. Didn't do anything like find top dead center.

    So now the question is do I have an issue with the health of the motor? There are plenty of reasons why it was going lean which I am basically hoping all the stuff I throw at it from what was a good running motor will fix it along with plugs fuel filter clean the maf with cleaner and q tips etc.

    I also pulled the intake and there is evidence of oil soaked into the ports on the heads so pretty certain it has been injecting oil which is common. Surprised that I didn't find any bent pushrods either.

    Let me know if anyone has thoughts on the compression numbers or run it till it blows up in front of the 55?
    Bryan Leinart
    CMC #24

  2. #2
    Senior Member Carroll Shelby
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    Checked the service manual and the numbers are okay. Also I didnt open the throttle blade on the second test and pretty sure we did on the first. That may explain it. Either way I'm less worried now but will still post pics of a plug. The deposits on the plug weren't there before the first test and only appeared after lean demo runs.
    Last edited by BryanL; 04-17-2014 at 07:47 AM.
    Bryan Leinart
    CMC #24

  3. #3
    Senior Member Carroll Shelby
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    Here is the worst plug-about one on each side of the motor looked like this.
    Attached Images Attached Images
    Bryan Leinart
    CMC #24

  4. #4
    Senior Member Grass-Passer MikeP99Z's Avatar
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    I think you need to flush the coolant system. The gunk from your radiator isn't burning correctly in the combustion chamber...

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    BL eureka you've discovered penicillin

  6. #6
    Senior Member Grass-Passer Suck fumes's Avatar
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    Running your car above 14:1 for any given time especially above 4k rpm can heat up and warp your valves if you keep running it like that. That's pretty crispy. If you try something else to fix it don't run it all the way through the rpm band if it starts getting lean again.

  7. #7
    Senior Member Carroll Shelby
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    RE: the oil getting sucked into the intake, are you running that updated fixed orifice PCV valve that's supposed to fix the issue?

    It also fits LT1s, stopped the "reversing of vent flow into the side of the TB" issue, but not sure how that translates to the LS1...

  8. #8
    Senior Member Carroll Shelby
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    I have only run it on the dyno and not much as we were trying a few things due to the a/f. But it only started it at first above 5,000. Pumped out the old gas and put in fresh. Same thing. Put in more gas to make sure it wasn't starving and same thing. Took the lid off and cleaned out the grass on the maf but same thing. Pulled the plate out and quit when it still did it.
    Now I'm swapping all my old stuff over as far as sensors intake injectors and a new fuel filter. Borrowing an a/f gauge to monitor.
    The PVC system was all stock. I'm swapping my vented catch can and closing off the vaccum ports on the intake to keep oil out of the intake. Then see if I can get the tune checked along with monitoring all th sensors. Then a stealth trip around the neighborhood a block from a police station. Or see if I can find a dyno to check it
    Obviously want to know it's fixed before tws.
    I will also be flushing the radiator for Patterson.
    Bryan Leinart
    CMC #24

  9. #9
    Senior Member Grass-Passer Hood's Avatar
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    Not sure if you caught what Mike was saying... it looks like you have a coolant leak into the combustion chamber, at least on that cylinder.
    Gary Hood
    CMC #20
    OH WOW! Racing

  10. #10
    Senior Member Carroll Shelby
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    Quote Originally Posted by Hood View Post
    Not sure if you caught what Mike was saying... it looks like you have a coolant leak into the combustion chamber, at least on that cylinder.
    Yeah just don't want to acknowledge that it might be a head gasket-if it is then I'm likely out for this weekend. Found a hole in the bellows that may have sucked in some unmetered air after the MAF-just wierd because the A/F wouldn't climb above 13 until upper rpms. A/F gauge is on it now and should be ready for a test drive tonight/tomorrow. I'll just run it around the neighborhood and do a short blast to see if the a/f stays in line. If it does then do it a few more times and pull the plugs.
    Bryan Leinart
    CMC #24

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