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Thread: Bucking and not getting full mm3

  1. #1
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    Bucking and not getting full mm3

    Having trouble figuring out why the truck is bucking right around 3,000 rpm and fuel rate dropping with tps at 100%.

    You can see on the log from 7:43 to 7:48 it starts pulling fuel. The truck is bucking through that and then shifts and everything is fine.




    Sixth Log.hpl
    Limiters 5th Revision.hpt

  2. #2
    Advanced Tuner JaegerWrenching's Avatar
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    Quote Originally Posted by Markcuckerberg View Post
    Having trouble figuring out why the truck is bucking right around 3,000 rpm and fuel rate dropping with tps at 100%.

    You can see on the log from 7:43 to 7:48 it starts pulling fuel. The truck is bucking through that and then shifts and everything is fine.




    Sixth Log.hpl
    Limiters 5th Revision.hpt
    Try raising this Forced shift.PNG

  3. #3
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    That one will raise the desired engine rpm for shift to occur at 100% throttle but if raised will probably still cause defuel but a much further drop in fueling due to some other limiters

  4. #4
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    Quote Originally Posted by Jim P View Post
    That one will raise the desired engine rpm for shift to occur at 100% throttle but if raised will probably still cause defuel but a much further drop in fueling due to some other limiters
    Any idea what limiter is pulling fuel? I'm out of town for work right now, so unfortunately I don't have access to the truck. The only other limiters I saw were limiter c and trans limit. I disabled them on a different tune and the truck wouldn't shift out of first without some coaxing.

  5. #5
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    Disabling those can cause some issues.

    Your rpm limits in the fuel-governors tab and I think fueling tab, very close to 3000rpm, raise them up higher to make sure the ecm isn?t running into begin defueling calculations. There are some delays in the transmission programming as well. I didn?t look too in-depth at what you have going on there though.

  6. #6
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    Quote Originally Posted by JaegerWrenching View Post
    Try raising this Forced shift.PNG
    Quote Originally Posted by Jim P View Post
    Disabling those can cause some issues.

    Your rpm limits in the fuel-governors tab and I think fueling tab, very close to 3000rpm, raise them up higher to make sure the ecm isn?t running into begin defueling calculations. There are some delays in the transmission programming as well. I didn?t look too in-depth at what you have going on there though.

    Thanks for the responses!
    I raised the WOT forced upshift, the high speed governor, and the all speed governor..... I still have the same issue, and now it's fueling more than the pedal map is commanding. Not sure why it would exceed the pedal map.

    You can see the fuel rate is higher than it should be from 2:59 through 3:07 then the bucking and defueling shortly thereafter.

    High Fuel Rate Still Bucking.hpl
    9th Limiters.hpt
    Last edited by Markcuckerberg; 04-26-2020 at 10:38 AM.

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    Your max commanded fuel rate is set to 160mm3, that's what the log hits so I'm not sure why you say its exceeding commanded, its literally hitting commanded. That being said, the max it actually hits is here...

    max fuel.png

    Fueling never goes outside the table. It tops out at 140mm3, you can set 200mm3 if you want but the fueling will not exceed whats in the 140mm3 column in the pulsewidth table.

    You are bouncing off of a bunch of limiters, reduce your throttle to fuel tables to 150mm3 where you have it set to 160mm3 in the 100% row.

  8. #8
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    You are hitting a trans limp, torque curve and altitude fuel limiters

  9. #9
    Advanced Tuner MAIDENCR's Avatar
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    Quote Originally Posted by Jim P View Post
    You are hitting a trans limp, torque curve and altitude fuel limiters


    Hey jim...do you know how to remove the torque curve limiter i have a weird issue on mine between 145 and 150mm3....at 145 my rail pressure start to drop(2kpsi) and at 150 when it switch on torque curve limiter it start to climb back
    03 cummins,175% flux injectors,dual cp3,s467.7/83 1.00
    Nv5600 with valair triple disc clutch