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Thread: Unknown Bucking???

  1. #1
    Lifetime Member hquick's Avatar
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    Default Unknown Bucking???

    I decided to post this here instead of continuing with my trany thread because I no longer think they're related.
    I've been slowly tuning for the past few weeks and cannot find the cause of this bucking I'm getting at low RPM high Kpa.
    The situation is, as I pull up to an intersection and then go to turn and accelerate...not particularly hard, the vehicle bucks alot.

    It seems this vehicle is a one off...there is nothing to compare it to.
    Please have a look at my log and tune and see if anything stands out?
    Is there something else I should try logging?
    Attached Files Attached Files
    Howard

    YOU ONLY NEED TWO TOOLS IN LIFE - WD-40 AND DUCT TAPE. IF IT DOESN'T
    MOVE AND SHOULD, USE THE WD-40. IF IT SHOULDN'T MOVE AND DOES, USE THE
    DUCT TAPE.
    IF YOU CAN'T FIX IT WITH A HAMMER, YOU'VE GOT AN ELECTRICAL PROBLEM.


    98 K1500 'HOLDEN' Suburban.
    Custom Whipple SC, Mercruiser Marine intake, 0411 PCM, 4L80E w/shift kit

  2. #2

    Default

    Can you give some more info about the engine? What plugs are you use and what gap are the set at?

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  3. #3
    Lifetime Member hquick's Avatar
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    Default

    Sorry...I knew I was leaving something out.
    98 4x4 Suburban
    5.7L Vortec
    Mercruiser Marine Intake
    Whipple SC
    2 bar MAP
    NGK...hmmm...TR6 or something (standard type plugs...not irridiums etc)...rings a bell. Sorry, been a while since I changed them. Gapped at .030 I believe...as recommended by many people.
    42lb Bosch green top injectors.
    4L80E transmission
    Running 98 octane fuel

    Thanks for taking a look
    Howard

    YOU ONLY NEED TWO TOOLS IN LIFE - WD-40 AND DUCT TAPE. IF IT DOESN'T
    MOVE AND SHOULD, USE THE WD-40. IF IT SHOULDN'T MOVE AND DOES, USE THE
    DUCT TAPE.
    IF YOU CAN'T FIX IT WITH A HAMMER, YOU'VE GOT AN ELECTRICAL PROBLEM.


    98 K1500 'HOLDEN' Suburban.
    Custom Whipple SC, Mercruiser Marine intake, 0411 PCM, 4L80E w/shift kit

  4. #4
    Lifetime Member hquick's Avatar
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    Default

    Frame 4631 - 4646 is where a marker is placed that the bucking was occuring at one stage of the log.
    Howard

    YOU ONLY NEED TWO TOOLS IN LIFE - WD-40 AND DUCT TAPE. IF IT DOESN'T
    MOVE AND SHOULD, USE THE WD-40. IF IT SHOULDN'T MOVE AND DOES, USE THE
    DUCT TAPE.
    IF YOU CAN'T FIX IT WITH A HAMMER, YOU'VE GOT AN ELECTRICAL PROBLEM.


    98 K1500 'HOLDEN' Suburban.
    Custom Whipple SC, Mercruiser Marine intake, 0411 PCM, 4L80E w/shift kit

  5. #5
    Unknown Zone TAQuickness's Avatar
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    Default

    Any chance you have a '98 RR?

    I had a very similar experience with my 383 and it turned out to be a combo of the throttle cracker, spark, and commanded AFR. Looking at my logs, nothing seemed out of the ordinary, but by focusing on each of the three above with the RR, I was able to, by trial and error, find a happy medium that eliminated the bucking.

  6. #6
    Lifetime Member hquick's Avatar
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    Default

    Do you mean a 98 Road runner?
    No...I'm running a 99+ 0411 PCM.
    I think I may be able to convince Jez to let me hook up his RR again.

    Thanks
    Howard

    YOU ONLY NEED TWO TOOLS IN LIFE - WD-40 AND DUCT TAPE. IF IT DOESN'T
    MOVE AND SHOULD, USE THE WD-40. IF IT SHOULDN'T MOVE AND DOES, USE THE
    DUCT TAPE.
    IF YOU CAN'T FIX IT WITH A HAMMER, YOU'VE GOT AN ELECTRICAL PROBLEM.


    98 K1500 'HOLDEN' Suburban.
    Custom Whipple SC, Mercruiser Marine intake, 0411 PCM, 4L80E w/shift kit

  7. #7
    Unknown Zone TAQuickness's Avatar
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    Default

    I'd throw the RR at it. The low load bucking can drive you nuts fast with the log/tune methods.

  8. #8
    Lifetime Member hquick's Avatar
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    Default

    Last time...we thought we'd sorted it with the RR. It doesn't happen every time.
    Is there something else I should be logging?
    Misfires?
    Howard

    YOU ONLY NEED TWO TOOLS IN LIFE - WD-40 AND DUCT TAPE. IF IT DOESN'T
    MOVE AND SHOULD, USE THE WD-40. IF IT SHOULDN'T MOVE AND DOES, USE THE
    DUCT TAPE.
    IF YOU CAN'T FIX IT WITH A HAMMER, YOU'VE GOT AN ELECTRICAL PROBLEM.


    98 K1500 'HOLDEN' Suburban.
    Custom Whipple SC, Mercruiser Marine intake, 0411 PCM, 4L80E w/shift kit

  9. #9
    Lifetime Member Doc's Avatar
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    Default

    I take it you are trying to do a OLSD tune here? I do believe that P0101, P0102 and P0103 -the MAF performance enablers need to be set to "A: 1 Trip Enabled" in order for the MAF to fail and truly enter SD. Until then I think you are just in some quazi no man's land where the pcm is really confused...Not truly being in SD or MAF operation.

    I do see you have the P0102 failure on you DTC page- I normally see P0103.

    Maybe somebody more informed can elaborate on this...

    However, in the frames you referenced in this post you are somewhat rich during the bucking event. I did notice a couple of really lean spots (tho with low counts) Specifically at the 1200rpms 65-70 MAP.

    Overall, your commanded fuel values in B3647 seem kind of strange. Are you viewing your commanded fueling in EQ ratio or AFR? In the tune tool under properties, Display Commanded Fueling should be set to EQ Ratio.
    The only reason I say this is because when I "flipped" that feature to AFR(you have to close the tool and re open it) then the commanded fuel values looked more in line with what one would expect to see for a setup like yours.

    I have found bucking usually come from an unintended error in commanded fuel, air or spark. Spark seems to be fairly steady in the highlighted area

    I didn't see any WOT during this latest posted log. Did you ever do so? In this log that is??

    Finally are you using a V1 or V2?

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  10. #10
    Lifetime Member hquick's Avatar
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    Default

    Thanks for looking Doc.
    I'll check into the things you mentioned.
    Yes I'm attempting an OLSD tune.
    I'm viewing commanded fuel in AFR. I was viewing in EQ but it was recommended I change to AFR.
    I haven't tried any WOT (basically I'm scared). Lol!
    I'm concerned about detonation and the amount of KR I'm seeing and am worried I'll do some damage. I'd really love to be able to plant my foot...even just once. Lol!
    Oh..and I'm using V1 running cos3.

    Thanks
    Howard

    YOU ONLY NEED TWO TOOLS IN LIFE - WD-40 AND DUCT TAPE. IF IT DOESN'T
    MOVE AND SHOULD, USE THE WD-40. IF IT SHOULDN'T MOVE AND DOES, USE THE
    DUCT TAPE.
    IF YOU CAN'T FIX IT WITH A HAMMER, YOU'VE GOT AN ELECTRICAL PROBLEM.


    98 K1500 'HOLDEN' Suburban.
    Custom Whipple SC, Mercruiser Marine intake, 0411 PCM, 4L80E w/shift kit

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