I'm still troubleshooting a problem with my 4L80e where it appears to 'let go' over 3rd at higher RPM and/or power levels.

Initially, I had assumed that this might be blowing through the torque converter (Circle D) unit. This was quickly dismissed, and has now been proven to not be the culprit, with engine RPM and ISS RPM maintaining a very similar pattern when the problem occurs.

I now believe the problem is after the torque converter, and have since installed a pressure sensor so I can log this data. The next challenge I have is, I can't simulate this problem on the street, as I run out of traction well before I would have the issue. I am aiming to get this back on the dyno ASAP, but in the meantime, I've gathered some data that I'm hoping will be helpful.

The engine is a 6.0L LS2, with an 88mm turbo running a maximum of 10psi (currently). The 4L80e is effectively a standard rebuild, with internal dual-feed mod, a couple of parts from the HD2 kit (no pressure relief) and a CircleD converter. I'm controlling this 4L80e with a P59 PCM, which had factory calibration for a 4L80e.

The pictures are just snippets of log files I've taken during street driving.




I'm seeing pretty consistantly ~100psi at idle and light cruising. ~150psi in reverse, and ~140-160psi under load. Are these pressures acceptable? Reverse works fine, 1-2 shift is firm, can't feel 2-3 shift at all, and 3-4 is barely noticable.

When racing, I was seeing the RPM flare at the top of 3rd gear. I did try shifting into 4th prior to the flare during 1 run to see what would happen, and it did flare after shifting into 4th aswell. I've added a log snip of the D3 run. Sorry no pressure sensor fitted when I was racing, that's a new addition.



I've also got this video of race-day where you can hear the slip, and I also dive into the logs a bit at the end of the video which might be helpful.


Would appreciate ANY advice anyone has that could point me in the right direction. 4L80e's are very rare in Australia and it is expensive/slow to get any kind of replacement parts. So, ideally, if there is a component that looks to be bad (e.g. pump) from this data, I'd rather order one now instead of pulling the box apart first.

 

Hey SirNemesis,

Very similar issue here with my 4L65E and 3rd/4th gear change. My tuner has indicated that my issue is related to the TCC lockup as the TCM is receiving a brake input and releasing the TC. This is troubling as I am not pushing the brake pedal but then highlighted a potential issue on my end - do I have this wired correctly? After looking at my installation, which the wiring was done about 5 years ago, I cannot seem to find direct input to my brake switch/pedal or a corresponding TCC input relay.
Guess my point is, have you checked your TCC channels and what is being called for in the logs?

 

Thanks for your reply. Unfortunately, I don't think my problem is going to be as simple as the TCC. The trend between ISS and VSS somewhat clears the TCC from any involvement as far as I can tell. TCC also works perfectly on the street (brake pedal switch working fine). During the dyno run, I had TCC disabled and manual controls locking the gear in 3rd with EFILive and the problem still occured.

I've just pulled the transmission out of the car to start some exploritory surgery. Hopefully something obvious appears...

 

my money is on that transgo sandwich separator plate. recommend binning that piece. dual feed it the traditional way.

 

Thanks truckdoug. The transgo plate was one of the HD2 parts I didn't use. I'm using the plate which came in the transmission.

 

I've just stumbled across this, and of course I stumbled across it while the transmission is fully disassembled on my bench.

Has anyone come across this before, or performed this fix? It sounds exactly like the problem I'm having.

 

Yes
While it is apart, vacuum test the AFL
Low AFL can cause these symptoms