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Thread: Cummins 5.9 Idle tuning issue

  1. #1
    Tuner in Training
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    Nov 2019
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    Cummins 5.9 Idle tuning issue

    Im having a hard time getting the truck to idle right. The idle speed seems to rapidly fluctuate between 600 and 800 rpm in a manner that is analogous of a gasoline engine with a vacuum leak. I wend through a bunch of revisions chasing some power and then later noticed the terrible idle. I tried reverting to an older revision but at 5 minutes a flash i got quite frustrated and continued tuning. Long story short, i killed the turbo before i solved the idle issue and now im waiting on a replacement. But in the mean time i wanted to better understand the parameters in the tune to hopefully find the idle issue.

    Im not too concerned with output power as the current tune seems to just demolish the tires, and my turbo but that may have been user error or turbo manufacturing error. But i would like to get the idle fixed up. What i don't completely understand are the governors, whats the highspeed, all speed, etc. Also i don't understand the droop and alt droop. The HP tuners description isn't quite explanatory for me. Sorry for the ignorance but im a gasoline guy , but ive been reading about diesel for like 2 days now and got a pretty good handle on inj timing, fuel pressure, and pulsewidth effect on each other. The truck was pulling pretty hard and put down some reasonable numbers on the dyno.

    tune is attached
    idles like crap
    Pulls hard AF
    No Smoke
    Attached Files Attached Files

  2. #2
    Banned
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    High speed governor - engine rpms above a preset threshold

    All speed governor - regular engine speed governor so long as not in low(idle) speed governor, high speed governor, boost limiter, or any other limiter.

    Droops are parameters to configure the behavior of the associated governor. Typically all those can be left alone. They govern engine speed just fine. When they don?t govern engine speed just fine anymore it?s because of something you done somewhere in the tune.

  3. #3
    Tuner in Training
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    Nov 2019
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    Thanks Jim, what tables effect the idle speed governor? I haven't found anything relating to that and i don't think i made any changes to it. But i would like to get the idle sorted out.

  4. #4
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    Whichever air density table the ecm is on at the time affects your idle. The low speed governor is just a pile of single value parameters for the most part operating in a PID loop to regulate the engine speed to the target idle speed.

  5. #5
    Advanced Tuner
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    Jun 2015
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    Sometimes I had idle issues after changing stuff and never really figured out what was causing it. When you say low speed governor where is that? I have looked and can only find high speed governor and all speed governor. I was looking back at a log and pilot pw pretty much stays the same and it just seems to change main pw to regulate rpm. Sometimes it over seems to over compensate or something and that is when the rpms aren't steady.