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Thread: 6L80 2-3 3-2 issue

  1. #1
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    6L80 2-3 3-2 issue

    Just finished going through the engine and transmission in my 08 G8. A friend and I rebuilt the transmission, it had 0 issues before we rebuilt it. The only reason I did was because it had 149k miles on it. The rebuild included a new GM friction kit, updated pump and cover,Sonnax O ring end plug kit,boost valve,1-2-3-4 apply piston, 4-5-6 apply piston kit and Hughes 2500 stall. I put everything together and followed a tuning guide and it worked great. I ended up with a lifter failure and went to a bigger cam. I had the car dyno tuned and the tuner did it in Speed Density (not my idea he said it was required because of inconsistent MAF which ended up being a missing plug on valley cover that I later found) and after the tune thats where I ran into this issue. Under around 50% throttle 1-2 shift is great barks the tires, same with 2-3 shift BUT I normally end up easing off the pedal around this point and the trans downshifts back to 2nd and will hold it for 3-5 seconds then shift back to 3rd. All other gears are fine and operates well otherwise. I have attached my current tune. I have 3.45 gears and 285/35/19 tires. Any advice is greatly appreciated. thanks
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  2. #2
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    I have been doing research and I see that the MAF is required for torque calculations so the transmission. i cant help but think something isn't set up correctly in tune.

  3. #3
    Tuning Addict 5FDP's Avatar
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    Post your stock tune as well. It helps to see what you did change from stock on the transmission.

    I personally wouldn't suggest having TM nearly completely disabled on those transmission too. Yours looks to have most of it off. Barking tires is cool and all but that is still hard on the transmission sometimes.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

  4. #4
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    Here is the 100% stock tune. I also changed the rear differential from 2.92 to 3.45 and used the gear tire wizard.
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  5. #5
    Tuner hivoltagedriver's Avatar
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    It looks like they have all of the pressures and volumes cranked WAY up, and all of the TM turned off. You want the shifts to happen quick, and need enough pressure to make that happen, but not so much more than that. And I agree that I would leave TM enabled, at least to some extent.

    I had over 110K miles on my stock 6l80 in my G8, behind 600+hp for a long time before I finally broke hard parts on a forced high rpm downshift. I'm on my work PC, and don't have any of those tunes handy to share though.
    2017 JKU Rubicon: Purple, long arms, tons, 40s, Banks CAI, Borla cat-back, TD2/HPT tuned, daily.
    2017 GMC Sierra SLT: 6.2/ 8spd. Just getting started on it...

  6. #6
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    I made a few revisions, lowered the line pressure etc. Would you mind taking a look to see if this looks more in line? Thanks
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  7. #7
    Tuner hivoltagedriver's Avatar
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    That looks better. How does it run with that tune? Also, are you reconnecting and re-enabling your MAF?

    Also, if you want it to drive way better, on the shift scheduling copy the upshift table from 50% throttle and up to the downshift side, then subtract 10mph. Then you can smooth into the lower cells. This will make your downshifts a lot more responsive, and not require you to poke is as hard to get it to drop a gear or two. Then make the WOT table match the 100% column in your part throttle table.
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    Last edited by hivoltagedriver; 1 Week Ago at 02:07 PM.
    2017 JKU Rubicon: Purple, long arms, tons, 40s, Banks CAI, Borla cat-back, TD2/HPT tuned, daily.
    2017 GMC Sierra SLT: 6.2/ 8spd. Just getting started on it...

  8. #8
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    It does better, I like the way it shifts but something is wrong. It did the 1-2-3 back to 2 today after I flashed that tune into it. right after that I was getting on the highway and kicked it down back to third and had a flare Ive never had. I think at this point Id be smart to just pay someone to fix the tune rather than smoke my trans. My car will stay is speed density, it has a SD operating system. I'm not crazy about that myself, thats what the tuner did.

  9. #9
    Tuner hivoltagedriver's Avatar
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    It sounds like you COULD have an internal hardware issue of some sort in the transmission.
    2017 JKU Rubicon: Purple, long arms, tons, 40s, Banks CAI, Borla cat-back, TD2/HPT tuned, daily.
    2017 GMC Sierra SLT: 6.2/ 8spd. Just getting started on it...

  10. #10
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    You have made large changes to the transmission pressures which will now upset the adapt values that have been learned with your previous pressures. I would recommend an adapt reset / preset and following the GM drive cycle procedure (you will have to find this, I don't have it on hand). At the very least, do this before throwing in the towel.

    Also, make sure adapts and torque management for EVERYTHING is as per factory default for your tune.

    With your previous higher shift pressures it may have been done like that as your torque model is off.

    A log would be nice. One that shows at least the following PIDs
    All PCS channels, 20Hz
    Torque converter slip, 20Hz
    TCC pressure
    Torque, 20Hz
    Torque management advance, 20Hz
    Trans slip rpm, 20Hz
    Trans current gear
    PRNDL Status
    Trans shift mode
    Time of latest shit (lol, shift) 1 through 6
    Trans fluid temp
    Trans Input shaft rpm, 20Hz
    Trans output shaft rpm, 20Hz
    TPS
    RPM
    Speed