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6l90 downshift rpm surge

Custom tuning includes both engine and transmission.


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6l90 downshift rpm surge

I'm trying to figure out a problem with a downshift in my V. I have attached an old log that shows it well at 1:58 into the log.  I've made some changes since and have other logs, but usually they are long.

On the log it shows as a 2>1 downshift. It happens in sport or touring mode. I thought that touring didn't downshift to 1st, but that's what the log shows. When decelerating, foot on the brake, when it reaches 10mph it makes it's last downshift. It's intermittent, but sometimes the rpm jumps up as it downshifts and actually pulls the car. On logs, I've seen the rpm jump as high as 1300 rpm and it can actually add a couple mph while I'm on the brakes trying to come to a stop. It pulls the car.

I've tried lowering the shift rpm for the 2>1 shift down to zero mph at low throttle positions. Didn't work. I tried turning the throttle follower settings back to stock (car has stock tb). Didn't work. I tried playing with Idle spark adaptive control for underspeed because it appears to happen when the rpm drops 50 or more rpm below desired. That didn't work. The tune has the tcc unlocked in 1-3 so that shouldn't be it. I've gone as far as putting a completely stock trans tune in it and it still does it. That leads me to believe it's not trans tune related.

I'm out of ideas. I contacted the tuner for help, but no response yet.  Does anyone have any ideas what I should look at? This isn't a major problem, but it's annoying and I would really like to fix it.

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