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Thread: Really poor shifts at light throttle in cold weather

  1. #1

    Really poor shifts at light throttle in cold weather

    I could use some advice on how to potentially tune out some strange transmission behaviors. It seems like there's a possibility of the offgoing clutches letting go before the oncoming clutches are ready. a shift gets commanded then the engine revs up as if it's in neutral then it grabs the next gear. This seems to only happen during low torque request and outside temperatures around or below 32F. If you request more torque from the 'go pedal' shifts are normal.

    I've attached a datalog that shows the pressures doing something that appears funky to me. It looks like it drops the offgoing clutch pressure then builds some pressure on the oncoming clutch but maybe not enough to fully engage the oncoming gear then the pressure drops and slowly builds back up I think this is when I'm noticing the feeling of a neutral gear for a second or so. It looks like it took about 1.5 seconds to build up what appears to be a holding pressure of 506KPa.

    *Another transmission question: should it be possible to attain 0 Torque Converter slip when it's locked and under acceleration?

    This is in a 2011 F350 6.7 Diesel. dual fuel pumps, larger turbo and a built transmission.
    Attached Files Attached Files

  2. #2
    One place I would look is would be the boost Pressure and time because these maps have the axis based on transmission oil temperature, and you are having issues at low temperature. from what i have read these maps affect the pressure to the offgoing clutch during the shift. Since the issue seems to go away at higher torque, I would look at how the shift pressure maps change as torque increases and change your pressures in the problem areas to be closer to that- in most cases this would be an increase in pressure. In theory when the converter is locked it should have zero slip. It probably wont be zero all the time but it should be close to it. What exacly is modified in your transmission? clutches, valvebody, pump, solenoids etc? Also when you first load a tune is the problem present or does it start to happen after a while? this might suggest that it is related to the adaptive shift time tables. Hope this helps

  3. #3
    Thanks CKrueg. I really appreciate the response. I've been trying to log with SCT because HPT just doesn't seem to have the params I need. Turns out SCT doesn't really have all the params either. I ended up using IDS to log with which was really helpful because I knew I was logging the right thing and seeing the correct values output to the log. The other thing that makes troubleshooting difficult is the temps are warming up. Sometimes I think I've got it figured out then the next cold day the problem resurfaces.

    I decided to focus on just one gear change (3-4) and see if I could affect it in a positive way. The thing that seemed to make the most difference so far was nearly doubling the boost time on Element E. Which really doesn't make sense to me. I thought boost was for the offgoing clutch not the oncoming. My understanding is E is oncoming and B is offgoing for the 3-4 shift. Another thing that seemed to help was reducing the overall slip time and initial slip time.

    The Converter is good I got it locked up well, the slip was just SCT LiveLink reporting bogus information. I really wish HPTuners would enable better logging for this truck. I've seen logs of other vehicles using HPT and it looks so much better to use than IDS or SCT.

  4. #4
    That does seem weird. Have you tried messing with the off going pressure or the boost pressure?

  5. #5
    I upped boost pressures on B and E 2 weekends ago and I thought I had fixed the problem however, a couple days later I noticed the problem came back. I haven't touched offgoing pressures.

  6. #6
    Also from one of Ford's Patent diagrams it sort of looks like boost get's skipped at light throttle.

  7. #7
    Maybe try raising the offgoing pressure and see if that helps.

  8. #8
    Did you ever figure this out. I am having a similar problem on the 1-2 shift at really light throttle on my 6R80.