I am on my second 4L80e in 2 weeks behaving the same exact way and am running out of ideas... When in light throttle and moderate acceleration, it shifts like a dream. When I get into the pedal the pressure mode goes to "diag max" and then my shifts are very hard from there in. (especially the 1-2). I am using HP tuners and have tried playing with the delivered torque settings in case that was to blame but still I am going directly into max line pressure but getting no codes or DTCs. The temps are also getting up toward 190 quickly before I shut it down and cool it off.

Vehicle is a 2007 GMT900, E38 ECM with T42 TCM. I have replaced the TCM with a new one, no change in behavior.

Is there any procedure or diagnostics I can do to prove its is or is not in the tansmission? I doubt I got 2 bad ones form completely different vendors twice.

 

Full reflash to OEM tune in both modules and see if problem goes away. If not start diagnostics from there

 

Thanks for the suggestion. Unfortunately its not an option for me. I have 88lb injectors, a cam, and a turbo and originally had a 4L60e so not only is my tune fully scaled 50% for the injectors but the TCM has a different OS now. Although this sounds like alot of variables, I see lots of guys on this forum have done these sorts of mods so I dont think I've created a Frankenstein or anything.

One interesting finding is that if I disable the diagnostic for "invalid torque singal - enable max pressure" then the trans does not go into that max pressure mode and shifts smoothly. It seems the problem has to do with the torque PID or some other delivered torque calculation in the ECM. That is where I'm stuck.

 

Is the MAF scaled correctly. Thats where the torque signal is derived from. If mafs all screwed up tranny's all screwed up.

 

Basically what I did to work around the 63.5 lb/hr limit is to take the IFR of my new injectors and Mulitply by 0.5. I then multiplied the entire MAF tables (low and high) by 0.5 as well. From there I scaled the spark tables. At this point I see my "delivered Torque" pid is reporting quite low. I have multiplied the Torque coef EQ table by 2 and that puts my delivered torque back toward normal but I suspect its not quite right since the trans goes into max pressure mode.

The more I look at this, the more I suspect the problem lies in the scaling of the tune. I've read quite a bit on the topic and found a pdf from dsteck on another forum but I dont seem to be having much luck with the results. I wish I could see what/where the transmission is unhappy with the expected ECM input.

 

It turns out that since I scaled parts of my tune for the 88 lb injectors to overcome the 63.5 lb limit in the ECM and since the ECM uses the IFR in part to estimate "Delivered Torque" PID ...and since the TCM uses that PID to determine shift points, shift pressure, etc, I had to also scale my transmission table axes. There were about a half dozen or so table axes to scale.

After that, I no longer went into "Diag Max" pressure mode and the shifts stayed nice an smooth. Hope this can help someone...I pulled quite a few hairs out finding this.

 

Thanks for sharing.