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

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.

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.

Here is the 100% stock tune. I also changed the rear differential from 2.92 to 3.45 and used the gear tire wizard.

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.

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

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.

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.

It sounds like you COULD have an internal hardware issue of some sort in the transmission.

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

Bringing this one back, cause I was curious and looking at your tune. I'm no expert, but I have my g8 6l80 shifting quite well. I noticed under adaptive, your oncoming volumes are all jacked up compared to stock. You have them all set at 60000 across the board. That's 200-300% more than stock is some gears. I'm guess that was a big part of your issue. Your pressures looked okay, I have mine set to higher in a couple areas and my oncoming preset is a good amount higher than yours in all shifts.

I'm still a bit confused why everyone jacks up their pressures. I've got a little more (10%) in the high torque / rpm regions upshift pressure tables and 0.15s in the high torque / rpm regions for shift times and that is it. Kept it simple. Trans shifts like a dream all day. If anyone finds anything wrong with the attached files please let me know so I can learn some more.

hjtrbo, I would be most concerned about your fuel pump not keeping up. In that log, you're dipping down around 43psi at 6500rpm

Hey, yeah scary aye. Known about it for a little while. I bought this setup...
https://aftermarketindustries.com.au...e-valve-system
Went with the twin 460's so should fix that up nicely. Looking to get it onto flex fuel E85 at some point.

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Originally Posted by hjtrbo

I'm still a bit confused why everyone jacks up their pressures. I've got a little more (10%) in the high torque / rpm regions upshift pressure tables and 0.15s in the high torque / rpm regions for shift times and that is it. Kept it simple. Trans shifts like a dream all day. If anyone finds anything wrong with the attached files please let me know so I can learn some more.

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6l80 vs 6l90 tunes are a bit different from the factory. I've got my pressures looking pretty close to your 6l90 tune. Only thing that caught my eye on your tune was your max line pressure table. It drops off in the upper RPMs which doesn't make any sense to me. My max in 4000 and 7000 is 1638 kpa.

My testing shows that table does nothing if you raise it on 6L90. It is stock on mine. Also torque drops off higher up so dont need high clamp prrssure. Have a play and see if you find the same thing. That's what confuses me about why people do it.