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Thread: Idle tuning help stalling

  1. #1

    Idle tuning help stalling

    Let me start by saying i went through the idle tuning sticky and i cant figure it out. Its a 6.0, 216/220 cam, turbo. My issue is it will start and then stall. It takes about 6 key starts to get it to stay running and then it will idle fine. Its better when its up to temp. Other than that it runs and drives fine.
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  2. #2
    Wrong idle startup log was attached
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  3. #3
    Tuning Addict 5FDP's Avatar
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    Yuor cylinder volume is way off, the computer thinks it's like a 4.5L engine and not a 6.0. So all of your calculation are wrong for the real engine size. You need to change that back to .74590 I believe.

    I'd fix that, make any VE table change to make sure fueling is spot on. Make sure you aren't having fuel pressure issue after the prime, maybe add a touch to the base running airflow.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

  4. #4
    It's scaled 25%. It started and idled fine before the cam and turbo with the tune scaled like this

  5. #5
    Senior Tuner
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    I don't know what you mean by "scaled 25%" but that
    alone creeps me out. There's very little about the tune
    that would want a "dumb" across-the-board falsehood
    applied.

    In my experience idle stalling comes from over-rich fueling.
    This has multiple actors (and I know little about the DBW
    throttle, there's probably more). The VE table is a big deal
    and cam overlap whacks that, at the low end, and you are
    going to have no chance of direct-fitting the 400RPM column
    (800RPM, you can at least force idle and get some valid AFR
    points to fit the rest against). The 400RPM column I have
    had to do "by eye" (curvature ought to look right based on
    the trajectory from above).

    Open loop fuel/air enrichment is a problem with big cams
    and worse when pressurized. You could be pushing the
    commanded fueling up because you're at higher MAP than
    before. You need to stay out of enrichment at idle and
    enough above idle MAP, that any surging doesn't tickle
    the enrichment "threshold", shoot big fuel and set up a
    yo-yo behavior with the idle RPM or idle airflow loops -
    IAC and DBW throttles can't (or don't) respond fast when
    the motor is "soggy". Some relief can be found in the idle
    air control P,I,D settings (tuning the loop) but you want
    to clean up the fueling first.

    Also a consequence of high idle MAP is low idle timing. This
    also destabilizes the idle control loops.

    I think you will be well off to go to a manifold referenced
    fuel pressure regulator if you haven't already. This can get
    rid of the pressure hassles and some injector response
    issues at the low end (can you really control injectors at
    very low duty / pulse width? If swapped, have you any
    info at all on short-pulse behavior (offset)?

  6. #6
    After it starts and stays running it idles at 14.7 afr in open loop. By scaling I mean I reduced the cylinder volume my 25%. Any table that was measured in g/sec was reduced 25% and the injector size was also reduced 25%. The reason for this was when it was n/a the timing was at .84 g/sec at 100kpa. Now it's at .60 g/sec at 100kpa after scaling. Leaving more room in the timing table for adjustments while in boost. It started fine with a scaled tune n/a stock cam. I think the best thing will be to unscale and see it that makes a difference.

  7. #7
    Tuner in Training
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    Compared to my centrifugal supercharged 6.0, I've got about 1.5 more g/s in my Idle/Airflow/Startup/Friction Airflow Initial at 68 degrees. You may want to try bumping up some values there and see if it helps.

  8. #8
    I have tried the following things with no success.

    1. Remove my 25% scaling back to stock
    2. Add airflow to friction airflow as Hoosier suggested.
    3. Reduce idle airflow at low temps (was at 25 g/s)

    Looking at my logs it starts, revs to 1200rpm then injector pulse with drops from 4-5 down to 1.6ms and stalls. For reference it needs about 2.9ms pulse width to maintain 1000rpm. Looking for any ideas

  9. #9
    Tuner in Training
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    Can you post your tune now that you've taken the scaling out?

  10. #10
    I don't know what I did but since I reduced idle airflow it starts fine now.