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Thread: High Speed Governor Kicking in?

  1. #1
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    High Speed Governor Kicking in?

    Hey there. I've had an issue with my truck since before I started tuning, and now with the proper scanning capability, I'm seeing some things.

    The issue has been that when I take off for the first time, my truck will hang in first gear, at about 2000rpm. The power rolls off softly starting around 1500rpm, and even with max throttle will only hit 2000rpm. I release the throttle pedal and repress and the truck will run normally the rest of the day. Sometimes if I hold the pedal, after a long delay, the torque will reappear as if a switch was flipped.

    The scanner is telling me that around 2000rpm the master fuel correction reason is going from 'Running Nor', which I suspect is running normally, to 'High Speed ...' which I suspect is high speed governor. I don't know how to expand the window in the 'channels' window to see the entire text string. Not sure what I'm missing there!

    Anyway, the settings for the governor are Low Limit: 1400, High Limit 3500, Setting 3500. Not sure what a low limit is for on a high speed governor? Starting point to start calculating limiting rate of rise of rpm perhaps?


    When the transmission asks for defuel for a shift, is this how it shows up in the ecm? I have had some shuttle shifting 1-2. Not bad, just occasional. I haven't yet replaced the transmission transducer and solenoid.

    Snapshot and settings enclosed.
    Attached Images Attached Images
    Last edited by cfoss1000; 05-14-2019 at 06:06 PM.

  2. #2
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    That 1400rpm low limit is the rpm above which refuel calculations are allowed to happen. If you are hitting the high speed governor at 2000 rpms you got some other issue going on. Does this occur when running stock tuning?

  3. #3
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    Yeah it did.

    I did some research, and didn't find much. I did find some info on the ISX. If they used the same idea, then I know more about how the high speed governor works. It seems like from the settings the governor works in the same way.

    In short if you are drawing lots of power it will allow the engine to spin to a high rpm.

    When not drawing much power it will only allow the engine to spin to a lower rpm.

    The transmission shift points should occur at a lower rpm than the governor activation, so you shouldn't hit the governor except at high speed in top gear, or top selected gear if manually selected.

    I suspect my transmission is not shifting on time from 1-2, and that the low load on the engine is limiting the rpm to 2k.

    Sound right?


    Chay

  4. #4
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    I just found the TV cable on frayed on the transmission end.

    It acted to prevent the throttle valve from returning to the idle position, which would cause a late shift.

    Hopefully this is my issue.

    Chay

  5. #5
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    There are multiple high speed governors all for different purposes, the engine tuning is generic for the vast range of applications the engine gets used in besides light duty automotive. The Chrysler specific flash files just have the transmission control algorithms and parameters laid into it that sets it apart from other flash versions.

    I?ve only ever logged high speed governor being set when engine rpm reaches the threshold. Till then it?s either at LSG, ASG, unless some other limiter like boost/fuel is hit.

  6. #6
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    It's hard to find solid info on how these actually work, what the setting mean etc.

    I wish there was more information available from Cummins. I will continue to look.

    Chay

  7. #7
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    Well, the issue persists. On the positive side, after changing the cable the trans shifts like butter at low power settings. Very nice.

    Onward and upward....


    Chay

  8. #8
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    I have found and fixed the issue.

    Turns out that it was a failed transmission output shaft speed sensor.

    I have read that the pcm looks at the input rpm and the output shaft speed and calculates actual gear etc.

    Fixed now.

    I had another issue I thought was related (Misfire over 2krpm), but it turns out to be a programming issue. I will raise another thread as it's a separate issue.


    Chay

  9. #9
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    Correct, it?s called NV ratio. Output shaft speed divided by engine rpm to get the NV ratio, ecm compares it to a set of parameters to determine which gear it is in and whether the TCC is engaged in lockup or not.