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Thread: Trans Overdrive Lock/Unlock on Highway

  1. #1
    Advanced Tuner coachcrow56's Avatar
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    Trans Overdrive Lock/Unlock on Highway

    I have a 2000 GTP--car runs great except for one thing. Cruising down a flat highway at anywhere from 50 to 75---even the slightest throttle position change causes the Overdrive to Unlock. What can I adjust with Hp Tuners to keep the Torque Converter locked under very light throttle position changes??

    Copy of my tune is attached.
    Attached Files Attached Files
    3.0 Pulley/CAI/1.6 HS Rockers/Hi Energy Comp Cam 76-802-9/LS7 Lifters/ZZP Intercooler/Headers/2500 Stall Converter/Autolite 104's/ZZP Fuel Rails/100 shot NOS/GMPP Sway Bars//I forgot the rest!!!

  2. #2
    Tuner ZeroBoostBuick's Avatar
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    In Torque Converter... TCC Apply/Release speed

    In Release... 4th tcc, change the 38mph to 37 mph.

    -----------------------------------------------------------------------------------------------------

    There is a factory glitch with the tcc/apply/release speed for the 4th apply... (and this could be why tcc is releasing because it might be confusing the ecm)

    4th apply, at 0 and 6.3% throttle, change from 42mph to 44 and at 12.5% throttle change from 44 to 47.... This is because you can't lock up the tcc in 4th gear before it even shifted into 4th.

    I hope you understand.

    Once you have that sorted in the "Normal",... copy and paste the whole table to the "Performance" as well.
    Last edited by ZeroBoostBuick; 06-15-2018 at 09:50 AM.

  3. #3
    Advanced Tuner coachcrow56's Avatar
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    I tried the changes you recommended, and it stopped the OD from hunting at low speeds. But on the highway, with the cruise set and anywhere from 60 to 80 mph, the OD will disengage if Throttle Position changes by as little as 2%. As the car starts down a downgrade, the OD will disengage, and then engage as the car starts up a hill or if Throttle Position increases. Is there any way to Tune this out??
    3.0 Pulley/CAI/1.6 HS Rockers/Hi Energy Comp Cam 76-802-9/LS7 Lifters/ZZP Intercooler/Headers/2500 Stall Converter/Autolite 104's/ZZP Fuel Rails/100 shot NOS/GMPP Sway Bars//I forgot the rest!!!

  4. #4
    Tuner ZeroBoostBuick's Avatar
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    Your "Torque Converter" TCC Duty cycles are not how I would have them... In the maximum parameters you have them set at 100 in all the boxes and minimum at 50 in all the boxes.... mine are much different

    I'll post a tune from a 2002 Grand Prix GT naturally aspirated 3800.... You can copy all the trans tables because they're not aggressive, they shift smoothly at all throttle positions, and took me a long time to come up with all those figures. I'll also post the Stock factory tune for the 2002 Grand Prix GT. So you can compare stock to what I did and what's on your tune.

    At least I think the "Torque Converter" TCC duty cycle "minimum" & maximum" is the area that's affecting your tcc overdrive lock/unlock.
    If that doesn't solve the problem, you can copy all the transmission tables one section at a time until things fall into place.

    Stock 2002 GP-GT tune 2002-GP-GT-Stock.hpt

    Modded Jan30_2017_Read-to-verify-tune.hpt
    Last edited by ZeroBoostBuick; 07-01-2018 at 05:27 PM.

  5. #5
    Advanced Tuner coachcrow56's Avatar
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    Thanks for your help. My version of HP Tuners (old) would not open your Modded file, but it would open the 2002 GT tune. So I copied some of the trans settings over to my GTP and I will try it out the next few days.
    3.0 Pulley/CAI/1.6 HS Rockers/Hi Energy Comp Cam 76-802-9/LS7 Lifters/ZZP Intercooler/Headers/2500 Stall Converter/Autolite 104's/ZZP Fuel Rails/100 shot NOS/GMPP Sway Bars//I forgot the rest!!!

  6. #6
    Tuner ZeroBoostBuick's Avatar
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    Here is a modded 2002 Grand Prix GT tune.

    It's a very mild tune for a stock 2002 gp gt with a downpipe.

    2002-GP-GT-mild-tune11_Dec31_2014.hpt


    I wouldn't use the TCC tables from a stock tune unless you're willing to make the changes to the fuckups from the factory for the 4th tcc apply around the 12% TPS.
    Last edited by ZeroBoostBuick; 07-17-2018 at 11:17 PM.

  7. #7
    Advanced Tuner coachcrow56's Avatar
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    I know this post is old. School is out and I have time to work on this. My software will not open the file that ZeroBoostBuick posted. I plan to drive 1700 miles from East Texas to the Grand Canyon in July to see my youngest son get married, and I don't want to deal with the trans "Hunting" all the way. LOL!
    Last edited by coachcrow56; 05-27-2019 at 10:24 PM.
    3.0 Pulley/CAI/1.6 HS Rockers/Hi Energy Comp Cam 76-802-9/LS7 Lifters/ZZP Intercooler/Headers/2500 Stall Converter/Autolite 104's/ZZP Fuel Rails/100 shot NOS/GMPP Sway Bars//I forgot the rest!!!

  8. #8
    Tuner ZeroBoostBuick's Avatar
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    4T65-Shift1.png4T65-Shift2.png

    See if any of these files you can open. All these files should have the same trans settings, or near the same at least when it comes to shift scheduling and tcc apply/release.

    2000_Impala3.4_tuned.hpt
    2002-GP-GT-mild-tune11_Dec31_2014.hpt
    98_Regal-LS-read-sept11-2013-.hpt

    If you can't open any of these files, maybe update the vcm editor to the latest one.
    Last edited by ZeroBoostBuick; 05-27-2019 at 10:45 PM.

  9. #9
    Advanced Tuner coachcrow56's Avatar
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    I made a few changes, using your settings, to my TCC apply/release. It worked and my trans no longer shifts in and out of OD. Thanks for your help.
    3.0 Pulley/CAI/1.6 HS Rockers/Hi Energy Comp Cam 76-802-9/LS7 Lifters/ZZP Intercooler/Headers/2500 Stall Converter/Autolite 104's/ZZP Fuel Rails/100 shot NOS/GMPP Sway Bars//I forgot the rest!!!

  10. #10
    Tuner ZeroBoostBuick's Avatar
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    I've glad it helped.

    When tuning these late 90's / early 2000's GM's, I always thought the transmission tuning was just as important as the engine.