Have a swap car with an extremely hard/harsh 2-1 shift. I finished up tuning the MAF on the completely stock L83/E92 with the 6L80/T43. Only tune modifications are normal standalone items, and a MAF curve to account for the intake tube. I hoped getting the MAF dialed in would cause the transmission to act right but it hasn't. The E92/T43 were flashed to known good/matching base files from GM TIS prior to any tuning.
The 3-2 is very firm, and the 2-1 is hard enough I think the tires bark at times. THe TCC 12v wire is connected to the brake lights and I've confirmed this is working with scan tool.
Does this sound like a potential tuning issue? or tune around issue? or is it most likely hardparts internal to transmission? Just looking for a little guidance from you guys who mess with these often.
Yes coasting to a stop 2-1 downshift. It's the same hard downshift as a fast stop, or a slow gradual coast down. When it grabs second you sit up in the seat a little and when it grabs first it's a VERY hard jolt. Like parts are going to break kind of jolt.
I can probably log the jolt with the accelerometer in the MPVI2, although I've never done that before.
I'll take a read from the TCM later today. So far it's just been programmed with MDI/TIS. The programming is completely stock.
I was going to go through the shift tables using the bluecat tool like I do with the 4speeds. What shift requests would be lowered? I thought about raising the 2-1 downshift so the car had more inertia to push through the downshift, or I guess I can see maybe lowering the 2-1 downshift so it basically happens at a dead stop and not rolling, keeping the trans in second while moving.
I had a similar situation with a 4l65e. It has an HD2 shift kit, the engine itself is stock.
-Slightly lower than stock values in the 2-1 shift speed tables in the first 3 MPH columns helped. Like you said, I basically come to a complete stop before it shifts 2-1.
-Base idle airflow at stock settings.
-Stock settings on the rolling idle speed and coasting spark helped smooth the overall stoplight experience. I found the motor was hunting for idle when coming to a stop when I tried to be cute messing with those items.
Also, I forgot to note, make sure the correct wheel size information is being used. I did a rollout test and calculated the inputs for my setup. Helped get things in line as well.
Last edited by eXo3901; 11-17-2021 at 11:38 AM.
Reason: wheel size comment
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