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Ls1 sputtering and down on power when hot

This is a discussion on Ls1 sputtering and down on power when hot within the General Help forums, part of the LSx Technical Help Section category; Stock LS1 from an 04 gto. It has relatively low miles. Around 20k original miles. It has been sputtering at ...

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    Ls1 sputtering and down on power when hot

    Stock LS1 from an 04 gto. It has relatively low miles. Around 20k original miles.

    It has been sputtering at high rpms anywhere after 4K.

    When it's hot or at operating temp it is noticeably down on power. Much more power when colder.

    Smells rich out the exhaust.

    Is burning some oil. (Quart a month) Absolutely zero oil leaks anywhere.

    Getting poor mpg. Never got above 15 mpg. Average around 12 mpg.

    No fault codes at all. Or misfires on scanner.

    Was dyno tuned a year ago. Only made 297 to the wheels.

    So what should I check first? Need some help on what could be my problem. Compression check? Any help is appreciated.


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    Check your fuel pressure for starters. Headers or stock manifolds? Is it running a MAF?

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    It has a MAF. BBK long tube headers. It's swapped in an rx7. Fuel pressure regulator is stock. Has 255 walbro pump, corvette filter.


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    What are the pressure specs for idle and should I have a gauge ran into the car for high rpm WOT?


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    Smiles for 9.5 Years cammed goat's Avatar
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    Phantom Black Metallic
    2004 GTO M6

    How long did the LS1 sit before you purchased/installed it? Are the harnesses okay? I ask as wiring/harnesses could be damaged/melted from the headers. Inspect spark plug wires for tightness/damage. If you haven't cleaned the MAF, clean with MAF cleaner. IAC should be cleaned with throttle body/intake cleaner. Check your throttle body and clean that as well as the IAC port gets clogged with carbon and will cause performance/stalling issues.

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    Quote Originally Posted by cammed goat View Post
    How long did the LS1 sit before you purchased/installed it? Are the harnesses okay? I ask as wiring/harnesses could be damaged/melted from the headers. Inspect spark plug wires for tightness/damage. If you haven't cleaned the MAF, clean with MAF cleaner. IAC should be cleaned with throttle body/intake cleaner. Check your throttle body and clean that as well as the IAC port gets clogged with carbon and will cause performance/stalling issues.
    Engine didn't sit too long and it has been running good for the first 15k of the swap. Plug wires and plugs are pretty new. I'll check connections. Need to inspect coil packs also. Any easy way to test them? Also I have good cleaner for MAF sensor and throttle body so I will do that. I watched MAF on graph and it was reading good.

    IAC is making a loud click and buzz when I turn on key. And idle is perfect. I will double check it though.

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    Quote Originally Posted by NickatinaREX7 View Post
    What are the pressure specs for idle and should I have a gauge ran into the car for high rpm WOT?


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    You should have around 58 psi at the rail. No need to get crazy with revving on it. Just run the rpm up a bit and see if you have any significant drop.

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