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Thread: Throttle fluctuation Cherokee SRT Whipple

  1. #1
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    Throttle fluctuation Cherokee SRT Whipple

    i have big problems with a 2014 Cheroke SRT Whipple.
    car runs nice on WOT and make 719PS but on part throttle the car is bucking.
    you can see in the log file the throttle fluctuates.

    the car is with operating system AH
    the same car with the same mods in the software runs nice. only difference is operating system AG

    I don't know whats the bug. maybe a problem with the TCM software?

    thanks for help.
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  2. #2
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    Can you give me the exact spot on the log time wise you are getting hesitation? Tough to tell whether its shifting gears or its bucking.

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    in this log file from sec. 37 to 45
    still in gear, only TP fluctuates. it seems to me the car is running in a torque reduction.
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  4. #4
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    Looks to be all timing related, its picking up knock. Are the knock thresholds lower in the AG? Any other work done to the motor etc? Forged or have a non factory cam?

  5. #5
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    You are going into open loop fueling by having your pedal voltage threshold so low, should never be that low, you are DUMPING fuel into it.

    FUEL>GENERAL>WOT Thresholds>WOT Pedal Thresh you have it at 1.8824 volts. This should be closer to 3 volts.

  6. #6
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    I think that is most of your problem, your spark is also reflecting the WOT spark table, its way way too low for the cruising speeds (10-11* and should be in the mid 20's cruising).

  7. #7
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    i think it's more a Throttle Air Flow issue.

    could you post your original file?
    ____DH INDIVIDUAL____
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  8. #8
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    What and where is the S/C Bypass Flap vacuum conneced to?
    ____DH INDIVIDUAL____
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  9. #9
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    DH are you seeing in his log where its going into open loop under regular driving? Surely that's the issue, hes cruising around and tipping into WOT with a commanded 12.8 AFR and 10 degrees of timing, and then a little lighter throttle and it switches to 14.7 AFR and mid 20's timing. that will feel like hitting a wall everytime.

  10. #10
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    thanks for the response.

    I will set the WOT Pedal Thresh near to 3V and will see what happens.
    Supercharger Bypass vacuum is connected to the manifold (intercooler housing) like whipple installation instruction.
    actuator and hose are ok.

  11. #11
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    WOT Pedal Thresh set so 2.8V and still the same problem. car is in closed loop and throttle oscillates.

    see in logfile 1:07 to1:29
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    Can you post up the original stock tune file?

  13. #13
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    EDIT: Nevermind, had a different tune open.
    Last edited by 06300CSRT8; 08-03-2015 at 03:51 PM.

  14. #14
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    I think its your Torque/Airflow Factor Offset table. looks very strange going positive and negative every 500 rpms. Never seen that before.

    Sorry sort of guessing here until you can post up a stock tune.

  15. #15
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    yes I saw the strange looking offset table. stock the table is also looking strange.
    the table in the tune files is only compared from a well working whipple Cherokee.
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  16. #16
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    I def think your issues are in that table, you see the pressure ratio scaling from the factory? Looks REALLY wacky, why would the factory calibration allow for an airflow calc at a 3x pressure ratio???? They contemplated the aftermarket running 42psi of boost???? Makes no sense, my guess is there is a bug somewhere in this OS that HP Tuners is reading and programming wrong.

    Based on the timing you are seeing at part throttle, tells me the PCM is calculating a very high airflow and giving you very low timing, and closing the throttle body to manage the high airflow. If you look at the factory calibration, in the upper two rows, you are mostly all negative values, and these are the pressure ratio areas you are in under part throttle.

    I personally would try making the values all negative -3 or -4 up to a 0.90 PR and from 3,058rpms down, then highlight and interpolate the rows to the value in the 6,752 column, see how it behaves.

    Torque Offset Table.JPG
    Last edited by 06300CSRT8; 08-04-2015 at 08:38 AM.

  17. #17
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    Also I am trying to see which hysteresis value is causing it, but its taking this jeep far too long to switch from DFCO (open loop) to closed loop, if you look at your log, it stays in open loop for almost 5 seconds after you apply the pedal, and the timing takes forever to get to a reasonable cruising level and you're getting knock, very very bad. I see KR in your log every time you go from coasting to accelerating. Recipe for disaster with that 6.4 and paper thin ring land.

  18. #18
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    maybe knock comes from forged pistons?

  19. #19
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    ha....slight detail left out, the motor is forged?

  20. #20
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    jop, forged pistons inside