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Thread: losing timing and hanging idle

  1. #1
    Tuner
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    losing timing and hanging idle

    stock 4.8 and manual nv 3500 swapped into 89 jeep wrangler.
    drivetrain, pcm and harness all from swap truck.
    wideband not hooked up for drive, but i know fueling is good.
    in my tune i have timing for "launch". but issue was present before that change.
    hanging rpm and timing dropping off has become more pronounced.
    failing cam sensor? crank sensor?
    ive posted before about this but have not gotten much response.
    i believe i have have everything for timing logged but cant see where its pulling it.
    base advance still good but actual goes super low(negative).
    towards the end of the drive is the hanging rpm.
    when i give high throttle at low rpm it hangs to the point if i push the clutch after letting off the throttle the rpms will rise.

    have attached log file as it sits and a drive home with lots of documented faults.
    if you think i should log something else please let me know.
    Attached Files Attached Files

  2. #2
    Senior Tuner
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    Mar 2011
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    You didn't include the IAC counts on the datalog. That info would help.
    Typically, you'll want it to idle with the IAC counts between 40 and 60.

    Try this modified tune and let me know how it performs.

    modify spark tables kw mod.hpt

  3. #3
    Tuner
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    as far as i can tell those changes wont effect when its happening. say at time 21:31 the spark corrections you did are the same as my file. 2000-2400 rpm .08 to 30c/g.
    sorry drove my tahoe today. so cant try it today.

    time 21:27 base advance 49* and no corrections but sae timing is -4.
    Last edited by shtboxyj; 11-12-2019 at 08:49 AM.

  4. #4
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    anyone else run into this? been trying to nail this down and dont want to just throw parts at it.
    also ive copied stock spark tables from my 02 4.8 tahoe and still getting issue.

  5. #5
    Tuner
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    figured out the hanging rpm was a bad maf. was going low 10 afr so burning the xtra fuel when i lift throttle. confirmed fueling is now good. i still have a losing timing problem at low throttle and low rpm. higher throttle % and rpm it never happens.
    Attached Files Attached Files

  6. #6
    Advanced Tuner
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    Dec 2011
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    San Antonio, TX
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    https://www.youtube.com/watch?v=wVyxH_bAit8

    Log all your timing and torque management channels and see whats going on.
    JTC Performance - Authorized HP Tuners Reseller
    Remote performance tuning

  7. #7
    Tuner
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    Quote Originally Posted by charcoal03silvy View Post
    https://www.youtube.com/watch?v=wVyxH_bAit8

    Log all your timing and torque management channels and see whats going on.
    did you look at my log? thats why im here. im logging everything advance and retard and nothing seems to be pulling it.

  8. #8
    Tuner in Training
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    Nov 2018
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    looks like DFCO is kicking in..as both fuel an timing are being pulled..
    Capture.PNG
    02 Silverado Z71 4x4 RCSB SS