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Thread: Upshifts Too Late, Downshifts Too Soon In One Truck But Works Great In Another

  1. #21
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    Quote Originally Posted by Supercharged111 View Post
    the cause of the bang shifts was me not doing a TPS relearn.
    Glad to hear you found the cause. I've never come across that before... so I've learned something new today.

  2. #22
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    Correction: went for a rip earlier and the dually was softer than I remembered so I shortened the min shift time to .3. My guess is that it needs to learn to the quicker times, but I suspect there's a way to land the base pressure so that less correction is required for shorter shift times. What might I need to log for that and how would I plot it? It's something I've been pondering for a bit. If it's the way ahead, then I have 3 trucks to apply it to.
    1998 GMC Sierra K1500 5.7/4L80E, longtubes, 411 w/COS 5, marine cam/intake, Whipple. 91 octane at 6000'.
    1997 GMC Sierra K3500 7.4/4L80E, 411 w/COS 3, Whipple, small cam.
    2004 Corvette Z06 with longtubes.

  3. #23
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    That's something which I can't help you with... hopefully someone else will be able to help. What I do is leave the line pressures stock and give it some more room to learn by changing {D1101}, {D1102}, {D1103}, {D1107}. There probably is a way to adjust base line pressures, but I would never be comfortable doing that.

  4. #24
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    Quote Originally Posted by statesman View Post
    Glad to hear you found the cause. I've never come across that before... so I've learned something new today.
    If I had corrected some of the known wrongs in my tune in conjunction with the throttle body swap and done a flash at the same time I would have not known it was a factor either (kinda odd that I didn't as I tend to flash something new into the truck most days). Made for a slower haul as I was afraid to give the thing any throttle with the trailer to try and keep the shifts as soft as possible but now that it's healthy again I can concentrate on some of the things you and Joecar have highlighted. The real prize was taking this back into posession.

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    Quote Originally Posted by statesman View Post
    That's something which I can't help you with... hopefully someone else will be able to help. What I do is leave the line pressures stock and give it some more room to learn by changing {D1101}, {D1102}, {D1103}, {D1107}. There probably is a way to adjust base line pressures, but I would never be comfortable doing that.
    Well there's another reason to fear base pressures as I currently do. Seems these tables would also need to be smartly coordinated with a shift in base pressure. Definitely going to poke around an 8.1 4L80E tune to scout for significant differences.
    1998 GMC Sierra K1500 5.7/4L80E, longtubes, 411 w/COS 5, marine cam/intake, Whipple. 91 octane at 6000'.
    1997 GMC Sierra K3500 7.4/4L80E, 411 w/COS 3, Whipple, small cam.
    2004 Corvette Z06 with longtubes.

  5. #25
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    Hooked up the trailer again and I must say it is much better than last weekend even if you ignore the smoother shifting. Deleting the kickdown has the transmission downshifting in a far more intuitive manner and having the TPS read properly I'm sure is also helping. I didn't find myself cursing the truck, just needs more power now. Shifts aren't even really that firm, but they are quicker now. I feel I now have the 90% solution as far as drivability, I can't imagine being stuck with a stock tune on one of these things with an automatic.
    1998 GMC Sierra K1500 5.7/4L80E, longtubes, 411 w/COS 5, marine cam/intake, Whipple. 91 octane at 6000'.
    1997 GMC Sierra K3500 7.4/4L80E, 411 w/COS 3, Whipple, small cam.
    2004 Corvette Z06 with longtubes.

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