This situation has been kicking my *** for a week plus. Long story short I recently swapped a 4L80E into my turbo 4.8L MCSS. The trans is a basic rebuild (soft, hard parts and updates) with a full TransGo HD-2 reprograming kit, Sonnax TCC lube pressure regulator valve (34200-14K) and TCC regulator/isolator valve (34994-01K), a FTI 4000 stall hard hit single disc converter (SRLS48082), a TCI deep pan, a 40K GVW Tru-Cool transmission cooler (because it has a FMIC and the final drive ratio is 4.56), and it is filled with Amsoil ATF. The segment swapped tune was taken from my LS-swapped '80 Lemans wagon which has ALL the same mods (except a slightly less aggressive triple disc FTI converter) and it drives flawlessly and has for about 8 years.

Back to the MCSS: everything is working well except the ECM will not command TCC apply but for a moment (and cycle it on/off). This is from the 15-01-00.hpl:



However, the TCC will apply fine if commanded through HPTuners (Force Motor Line Pressure does seem to be high (full) at times in this log (15-13-55.hpl)).




I have ensured that:
The fluid is up to temp (130*F to 153*F);
The misfire tables are maxed (were from the source tune, both cars have raunchy cams);
The wiring is correct (I have not tested for resistance across the pins, but that shouldn't stop the ECM from commanding the TCC); and
The tune does not command disengage speeds higher than engage speeds (again, I had a known good tune to base this on).

Additionally I have tried using the "performance switch" to jump between tables to see if there was something in the "normal" tune, and running it up to a "questionable" rate of travel to see if it met a missing condition. The only things I need to do now are make an adjustment to tweak the VSS as it is off by about 10mph - but, the VSS is still seeing enough speed to meet the conditions for the TCC to apply, and put a pressure transducer on the case to tune everything in to spec/taste.

Any ideas or recommendations would be appreciated.

Cheers!

 

I started to suggest misfire tables.
80s are easy to pinch the seal on the input shaft that feeds the lockup. Maybe the ecm is seeing slip and disengaging? Kinda of a shot in the dark on my part.

 

Logged the wagon today, same drive cycle as the first log above. There are some dramatic differences between the two vehicles. Including, but not limited to the MCSS not showing any data under Engine Load %, Trans Shift Mode as Cruise (vs Normal or Performance), and the TCC Slip % is under 100% (as if 133% is achievable) and the TCC Slip RPM is closer to 0 as opposed to -800... and the TCC Slip Off flag isn't triggered. The most perplexing things are the Turbine Input, Turbine Output, and Turbine Speed numbers as they do not correlate between the two cars... is it possible that I have the ISS and OSS swapped?

It is also worth noting that the wagon does have a functioning pressure transducer logging line pressure.

 

Possibly try changing the Minimum throttle release data. Have you logged KR, misfires, TM? I may have glossed over it.

"Minimum throttle release
- this sets the TCC to Off when ever the TPS is below the thresholds
- there are two vehicle speed modes, high speed and low speed
- for each mode there is a low TPS threshold, if the TPS is below that threshold the TCC will switch to Off if the PCM is not in Coast mode.

From what ive seen the 4L80e cals do not use the Coast mode, but let me know if this new stuff just doesn't work for you and you see TCC Mode as "Coast" at any time.

When you set the thresholds it's probably a good idea to make sure the TCC will unlock at low throttle and low speeds, so try to change the VSS modes and high speed thresholds only as a first attempt.

I have also added a bunch of TCC related status bits to the scanner which will help you see why the TCC is changing to "Off". There are a lot of reasons why the TCC can be set to the Off mode.

eg.
- TqMgt or Misfire request Off
- trans is in 1st gear
- trans cold
- brake is on
- TCC fault
- slip related
- min throttle mode (the new params control this)
- large negative or positive TPS transients
- Off during upshift or downshift
etc."

 

So my hunch that the inverted ISS and OSS data was an indication of their plugs being reversed was correct. I checked the wiring on my wagon and the instructions (again) to verify that the blu/wht and red/blk pig tail goes to the FRONT sensor. I am leaving this information here for anyone in the future who may make the same oversight... it seems that most people don't report back after solving this issue as it is pretty simple and a bit embarrassing. Hope it helps.



I also found this helpful in diagnosing the issue:
https://forum.hptuners.com/showthrea...l=1#post275698

Thanks to everyone who weighed in!

The rolling burnouts are hilarious in this car.

 

glad you figured it out, and updated the thread. i try to do the same but dont always succeed.

 

Yes Thanks for updating as most people sadly dont,