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Thread: 4l80e shifts won't shift until redline

  1. #1
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    Default 4l80e shifts won't shift until redline

    I have a 2003 6.0 with 4l80e DBC swap in 89 FS. It will not up-shift until almost redline. The only things that seems to affect it and get shifting closer to where it should be is if I change VSS pulse/revolution from 40 to 20. Trans is an early 90's 4l80 with newer harness and solenoids. I've tried multiple tunes and PCM's (DBC, express van PCMs from 03 and a few 03 Silverado PCM's with the IAC drivers). Any ideas on what I can try next? I am using OS 12592618
    Last edited by bubba68ss; January 18th, 2016 at 08:25 PM.

  2. #2
    Joe (Moderator) joecar's Avatar
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    Post tune file.

    Your 4L80E should have a 40x VSS reluctor...

    do you have ISS connected to PCM...?

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    ISS is connected.

    Here is the latest tune I have tried.

    2005_DBC_6..0_4l80e.ctz

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    Take a look at D0910 and D0925 - you have the shift logic backward. Upshift speed must be greater than downshift speed. Your part-throttle shift tables look OK - but only glanced at them, did not look cell by cell.

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    I see that. Could that be causing all my problems?

    I looked at a stock 6.0 4l80e tune from tunedepot and it has the logic reversed as well. http://www.tunefiledepot.com/calibra...(12212156).ctz

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    Some OEM tunes have the WOT shift logic backward - we as tuners strive to improve upon the OEM tune.

    D1206 to D1209 (I think) determine the TPS% when the PCM will use the WOT parameters. If this vehicle shifts OK below about 80% TPS, but then fails to shift property at WOT - then this is likely the problem (or one of the problems). I generally set the last 3 cells of the part-throttle shift speeds to the same value as the WOT speed - for each respective shift.

  7. #7
    Joe (Moderator) joecar's Avatar
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    And the other WOT shift MPH parameters are backwards also (e.g. D0915 and D0930, D0920 and D0935).


    The rule is (applies to all MPH shift parameters/tables): downshift MPH must be below the upshift MPH...

    this difference in downshift/upshift MPH is called "hysteresis", you want it to be about 5 mph or greater.
    Last edited by joecar; January 19th, 2016 at 03:07 PM.

  8. #8
    Joe (Moderator) joecar's Avatar
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    Also, set D0960,1,2 Throttle Kickdown to 100% all cells (otherwise these interfere with the PT upshift/downshift tables).

  9. #9
    Joe (Moderator) joecar's Avatar
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    Yep, stock truck files are the worst offenders, it's a wonder they shift...

    they are also the worst offenders for PE enabling, I'm shocked at GM.

  10. #10
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    Which PIDs should I watch that could reveal any potential problems? After I change the up shift and down shift points of course. ISS? OSS? Commanded gear? Anything else?

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