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Thread: Transmission tuning help - 8L90e

  1. #1
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    Exclamation Transmission tuning help - 8L90e

    Hi Guys,

    I have a jeep wrangler outfitted with the GM L86 6.2L Gen 5 Engine and 8L90e transmission out of a 2015 Cadillac escalade. The Jeep runs and drive but I believe that there is a lot of room for improvement when it comes to the transmission tune that the installer is using. Therefore, I am spending some time looking at the current tune and trying to understand why the transmission shifts so poorly.

    First and foremost, here are a few things worth noting:
    +The modified Jeep and the escalade weight nearly the same (5,000 ~ 6,000 Lbs range).
    +The jeep is geared at 4.10 and runs 35" (true to size) tires and the escalade usually comes with 3.23 gears and 32" tires.
    +The escalade has a top speed of 130 MPH (not sure if it is governed or not, but the car is made to handle that speed) whereas the Jeep should be limited to 100 MPH.

    The issues I am facing with the current transmission tune are listed below:
    +The transmission is very quick to upshift and stays most of the time in 8th gear. It feels like it's lugging the engine.
    +When you depress the pedal hard enough for the transmission to downshift, it drops too many gear and ends up going back to the 8th gear shortly after.

    I have a few general questions when it comes to the VCM editor software:

    1-Windows software usually come with a help menu that is indexed and that explains the software's operation and parameters. It seems that it isn't the case with the VCM editor. Is there a manual that can be downloaded? If so, can you please share the link.

    Update on question 1: found the link. Here it is: https://www.hptuners.com/help/
    However, this help guide applies to version 2. We are at version 4... Is this going to get updated soon?


    2-Is there a parameter hierarchy guide that shows which parameter supersedes the other? Let me explain. Looking at the WOT shift RPM vs Shift - Normal table, I noticed that shifting from 1>2, 2>3, 3>4, 4>5 and 5>6 is set to 5,600 RPM. However shifting from 6>7 and 7>8 is set to 8,192 RPM! My engine simply cannot rev at 8,192 RPM. Therefore there must be a parameter set in another table that supersedes this table values and limits the engine to the max governed 6,400 RPM limit. Moreover, according to this table, the transmission will never upshift to 7th and 8th gear, because the engine will never rev that high.

    3-Is there a table hierarchy guide? If so where can we find it?

    I also have a question regarding the WOT Shift Speed vs Shift ? Normal Table. Here are the parameters:

    2>1 | 19
    3>2 | 36
    4>3 | 59
    5>4 | 76
    6>5 | 107
    7>6 | 313
    8>7 | 313
    1>2 | 23
    2>3 | 42
    3>4 | 63
    4>5 | 81
    5>6 | 94
    6>7 | 313
    7>8 | 313

    How is the transmission supposed to upshift 5>6 @94 MPH and downshift 6>5 @ 107 MPH ?
    It doesn't make any sense.

    Also why is the 313 MPH value even used in this table?
    update: It turns out that by using the 313 MPH value which isn't attainable, the transmission will never upshift to 7th or 8th gear at Wide Open Throttle (WOT).


    Thank you!
    Last edited by Dlanor82; 08-07-2019 at 05:57 PM.

  2. #2
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    sounds like a fun toy. might get more info if you post the tune file. not sure id be any help, but im curious to see tune file

  3. #3
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    It is very similar to the 2015.5 Yukon Denali L86-8L90E stock tune. It is attached for your review.
    Attached Files Attached Files

  4. #4
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    thanks for sharing. maybe to help with your questions.

    1) only help ive seen in the program is when you hover over a setting , in the lower bar it will give description and min max variables.

    looking at your tune, in the speedo tab, you have 2 different tire settings (one for ecm,one for tcm) and they are different. the math i used came up with 576.526 for 35" tire . and i would change the gear ration to 4.10. will help it make correct gear changes if it has correct info. not sure what you used for tcase , but you could put that info in as well for 4lo operation

  5. #5
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    Thank you for the feedback.
    The tune I uploaded was the stock tune before modification.
    I did change the tire size in the Edit > Gear/Tire Wizard menu.

    However I have always wondered where one could enter the transfer case ratio. In my case, the transfer case ratio is 2.72:1
    Where should this be entered?

  6. #6
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    Quote Originally Posted by Erik Dicus View Post
    thanks for sharing. maybe to help with your questions.

    1) only help ive seen in the program is when you hover over a setting , in the lower bar it will give description and min max variables.

    looking at your tune, in the speedo tab, you have 2 different tire settings (one for ecm,one for tcm) and they are different. the math i used came up with 576.526 for 35" tire . and i would change the gear ration to 4.10. will help it make correct gear changes if it has correct info. not sure what you used for tcase , but you could put that info in as well for 4lo operation
    Do you mean the boxes under "Speedometer", then "calibration", then "sensor calibration" and VSS Tire Revs per": " Dist" and "Dist - Trans" both need to read the same?

    Mine reads "Dist" 598.02 and "Dist - Trans" 358.06 once tuned for 4.56 gears and 35 inch tires.
    Stock "Dist" was 680 and with 3.42 gears and 30.5 inch tires wit "Dist" that says 660.

    I dont have the stock "Dist-Trans" because the original tuner "lost' my stock files.


    How do we get the "Dist-Trans" number....or what is it? (Im still trying to polish out some trans tuning issues, a new tuner tuned a hybrid v6 camaro tune into my colorado and its good when driven in anger but a little rough when driven around)...Ill post it in a second

  7. #7
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    18 colorado v6 zr2, 35 inch tires, 4.56 gears, GM intake, afe exhuast....8l45 trans....
    Attached Files Attached Files

  8. #8
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    fifty, those numbers need to match. one is for the ecm and one is for tcm to reference. i came up with 576.419 tire revs/per mile.

    math is : tire diameter x 3.14 = rollout (circumference) in inches

    rollout divided by 12 = rollout in feet

    5280 divided by rollout in feet

    thatll usually get you close, ive found best number to be from ground to center of axle times 2. hope this helps
    Last edited by Erik Dicus; 08-15-2019 at 07:45 PM. Reason: grammar

  9. #9
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    Quote Originally Posted by Erik Dicus View Post
    fifty, those numbers need to match. one is for the ecm and one is for tcm to reference. i came up with 576.419 tire revs/per mile.

    math is : tire diameter x 3.14 = rollout (circumference) in inches

    rollout divided by 12 = rollout in feet

    5280 divided by rollout in feet

    thatll usually get you close, ive found best number to be from ground to center of axle times 2. hope this helps
    Thanks Erik. So I should change the “Dist-Trans” to 598.02 as well? I am using the revs per mile from the tire manufacture. But I’ll double check that right now. Edit: just confirmed 598 From Toyo RT website for 35/12.5/17

    I wonder where the differing “dist-Trans” numbers came from?
    Last edited by fifty; 08-15-2019 at 07:58 PM.

  10. #10
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    use the manufactures info if you have it. You can double check it with a gps or phone app.

    The other is someone messing with something they shouldnt have, or not paying attention.

  11. #11
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    I went back to the original trans tune and the vss and vss trans are different. They apparently should not be identical.

  12. #12
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    can you post that tune so I can see what the variance is?

  13. #13
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    It was 680 and 425. I’m not at home so i wanted to just get this up quick from
    Memory.

  14. #14
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    so doing some research , there is a high and lo resolution vss signal. havent found any info on what the parameters used are. be nice if they were labeled correctly in hp tuners for what they really are. but for research puposes , i took 680 divided by 425 = 1.6 , so if we are looking for 598 i took 373.8 x 1.6 = 598.08 . so maybe try 598.08 / 373.8 and see if it makes it happy . was able to read most of your post up till now, been at this awhile i see. just my .02 .

  15. #15
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    a 2016 cadillac ATS shares same trans , downloaded a stock file 814.33/500.50 = 1.627 . current is 598.02/358.06 = 1.670

  16. #16
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    Thank you for the feedback.
    The tune I uploaded was the stock tune before modification.
    I did change the tire size in the Edit > Gear/Tire Wizard menu.

    However I have always wondered where one could enter the transfer case ratio. In my case, the transfer case ratio is 2.72:1
    Where should this be entered?


    in the low adjust , under final drive. its the multiplier for low range
    Last edited by Erik Dicus; 4 Weeks Ago at 01:06 AM. Reason: clarity

  17. #17
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    Ok, so if the final drive ratio is 4.10 and the transfer case multiplier is 2.72:1 how do you calculate the low adjust value ?

  18. #18
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    you put 4.10 in the 2 boxes below final ratio , and 2.72 is the low adjust value
    Last edited by Erik Dicus; 4 Weeks Ago at 01:24 PM. Reason: clarity

  19. #19
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    I don't think that is correct.
    I have the Yukon Denali default tune and it shows a low adjust value of 0.73
    The Denali comes with a 2.69:1 transfer case
    Also, hovering with the mouse over the low adjust displays the following explanation: final drive ratio is divided by this when in low range.

  20. #20
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    You are correct, I miss read it when i looked at it today.