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Thread: 3800 SC Part Throttle Knock (KR)

  1. #1
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    Question 3800 SC Part Throttle Knock (KR)

    Original owner of a 1999 GTP with 122,500 miles. Had the phantom stalling issue the past few years and threw new sensors at it the few times I returned home. Replaced the MAF in December and drove it hard for the first time in awhile. Immediately noticed power hesitation and misfiring at moderate acceleration (~60% TPS). This was repeatable as seen in the first log.

    Should the engine be cutting power so much with low KR? And how is it possible for the MAF reading to decay to 0 Hz? The thing is, I'm certain I've had KR in the past since I went to a 3.4" pulley many years ago with only a CAI as a supporting mod. Yet no power hesitation or misfiring until recently.

    Mods
    LS7 hyd lifters @ 121,860 miles
    Front stainless powerlog @ 120,649
    Wizaired CAI @ ~100,000
    ZZP 3" downpipe @ 95,00
    Front powerlog @ 82,000
    Alternator voltage booster @ ??
    GMPP 2.5" catback exhaust @ 61,928
    180 tstat @ 51,700
    3.4" pulley @ 40,666
    MSP CAI @ 12,291 miles
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    Last edited by Amped; 03-02-2015 at 12:35 PM.
    1999 GTP / 2005 GTO / 2009 C6

  2. #2
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    Then in January I finally took apart the top end to replace the LIM gaskets. Spent a few days cleaning the LIM, throttle body, valve covers, and supercharger housing. New coolant, engine oil, water pump, and gaskets. Also replaced the crankshaft position sensor. No change in part throttle KR, so I proceeded with a desktop tune copying over most parameters from a DHP 1.5 style bin in the repository. Same results but the KR has increased. Is this just a tuning issue or is something else going on?
    Attached Files Attached Files
    Last edited by Amped; 03-02-2015 at 12:35 PM.

  3. #3
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    Check your knock sensors, I kind of had the same thing and just recently took the engine out and noticed the rear knock sensor needs replacing, its basically fell apart inside. It was saying I had 10deg of knock so pulled 10deg of timing out of the tables and it was still there.

  4. #4
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    Did the KR change when you originally pulled 10deg of timing? If the KR sensor was easier to access, I would probably start by changing the sensor. However, I don't get a CEL or any DTCs.
    1999 GTP / 2005 GTO / 2009 C6

  5. #5
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    The knock was still there so I knew something was up and I was running less than standard timing and 94 fuel. At 10deg or KR constantly my pistons would have melted, when I had the engine apart it was perfect inside the bores.

    The front sensor you can get to from under the car but the rear one might need the manifold taken off to get to.
    Have you tried pulling a chunk of timing out to see if it reduces??? Or try to disconnect one sensor at a time to see if things change.

  6. #6
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    thats plenty of mods for a grand prix to be on a 3.4 pulley. ive been in the 3800 world for along time and personally have a built 2001 grand prix gtp. so i know alot about them.

  7. #7
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    I hope I can help. it's only advice.

    Put good amount 105 octane and hope it's false knot, And take a look at the power enrich / ADD vs RPM vs Time. It look half filled in with zero.

    Don't give up. this is the best part of learning.
    Last edited by 507; 02-28-2015 at 08:13 AM.

  8. #8
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    Quote Originally Posted by 507 View Post
    I hope I can help. it's only advice.

    Put good amount 105 octane and hope it's false knot, And take a look at the power enrich / ADD vs RPM vs Time. It look half filled in with zero.

    Don't give up. this is the best part of learning.
    I believe the Power Enrich/ADD vs RPM vs Time table is that way in the DHP style tune because the Base AFR was lowered. Those tables were closer to stock in my first post, yet I experience light KR, misfires, and loss of power during the same conditions.

  9. #9
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    Do compression test to make sure your cylinders are not losing pressure.

  10. #10
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    I suppose, but the engine runs strong except for that 55% to 68% throttle position (and possibly WOT). Surprised that this knock increased with the DHP 1.5 bin. I've been reacquainting myself with HPTuners. Did some MAF tuning yesterday to lock down the LTFT. Hopefully I'll have time this weekend to scan and reduce timing in the main spark table.

  11. #11
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    Exclamation Eureka?

    Dropped the timing "lightly" in the KR trouble areas. Scanned again on my test route and though the KR has dropped a small amount, the car still falls on it's ass during part throttle! And more than ever, the MAF reading drops to 0 at those times despite holding the throttle pedal! I still don't know how that would be possible on a mechanical throttle linkage.

    So for shits and giggles I installed my old MAF sensor. I didn't scan today, but experienced no hesitation or power loss during part throttle and WOT!!!! I guess that NIB Delphi MAF sensor I installed in December is no bueno.
    Last edited by Amped; 03-10-2015 at 02:23 PM.

  12. #12
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    congradultion Amped, I'm glad it work out for you.