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Thread: Breaking up under boost

  1. #1
    Join Date
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    Question Breaking up under boost

    Been fighting this breaking up and can't figure it out. It's reacting to changes in plug gap, fueling and timing. Some things make it worse. Some better. But it never pulls clean as soon as it breaks over into boost it acts up.. Iv been from 11-22* timing. Fueling from 11.0-12.0afr. Plug gap from .020-.028. Tried tr6 and br7ef plugs. Runs fine until it breaks over into boost. It's on 8lbs. Doesn't matter if its 2500 or 5500 rpms. Same breaking up.. Runs completely normal until it gets in boost. Ideas??
    Slowest in Oklahoma...

  2. #2
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    Aug 2007
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    Honeywood, Ontario
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    Shitty plug wires? Coils getting weak?
    2006 Silverado
    Little Black Bitch

  3. #3
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    Brand new wires. Also swapped coils from my other truck. No change. The coils are relocated to the firewall though. A buddy thought might of been a bad ground to coils. But ran a ground straight to them with no change
    Slowest in Oklahoma...

  4. #4
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    Everything you listed are good things to check and adjust; they all seem correct.

    I had the same situation with my truck a while back with a new set of heads.
    Turns out a couple of the valve seats weren't 100 percent and as soon as boost came in I'd hear small backfires and stumbling. Just like when the plug gap is too wide.
    I know you'll hate to hear that but just a possibility.
    Last edited by farmtruc; 07-24-2013 at 02:24 PM.

  5. #5
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    Now that would suck. Any way to tell which side or way to tell without pulling heads? This isn't a small backfire and miss. It's pretty bad lol
    Last edited by ecld_07; 07-24-2013 at 02:41 PM.
    Slowest in Oklahoma...

  6. #6
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    You'll need to perform a leak down but that probably won't tell you which one because all cylinders will be very close.
    Forget doing a compression test; too general for something so specific and sensitive; only when in boost.
    To be honest my truck was fine before the new set of heads and the new heads were the only change so...
    Pulled the heads after a leakdown wasn't good enough, flipped them, filled chamber with water and watched them leak.

  7. #7
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    Dammit....
    Slowest in Oklahoma...

  8. #8
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    Sep 2008
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    I have heard of the spark getting blown out under boost, but if you have tried closing the gap it doesn't sound like the issue. I know some plugs are designed for this type of issue to protect the spark, but I will try and find the thread from pt.net.
    ECSB 2kSierra 2wd 4.8L-K&N-HPtuners-Calspeed LT's-Magnaflow-Tahoe20's-HankookRH06

    waiting to go in... 3.90s, 214/220cam

  9. #9
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    I was troubleshooting the same issue on my 5.3 when I melted #7. When I tore it down I found 2 exhaust leaks at the manifolds that I never aware of. I'm not sure if that was part of my problem or not but it sure makes me wonder.
    99 rcsb silverado...... boosted.

  10. #10
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    He's only pushing 8lbs and has the gap set small, even stock plugs gapped correctly won't blow that out.
    I think ur referring to the plugs that have the unexposed tip, like the tr7/9?

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