Trans Shifts too quickly and engine/trans OS compatibility

[dzoot]

Hello all,

I got a 6.0 L77 4L70e combo that upshifts very quickly to the point that it just lugs the motor all the time. Shifts are also very soft, shift timing doesn't change regardless of throttle input and the transmission will never downshift with throttle input. It basically acts as though the TCM isn't getting, or using, throttle angle data. The engine runs well and the only real symptom is the trans issue.

I got this combo from someone else, he bought it several years ago but never ran it. It came from a "reputable" LS powertrain shop as a "plug n' play" powertrain package. The harness was built by them and it was allegedly "tuned". It has been long enough now they won't help and don't have any suggestions as to a solution.

Going over everything I've determined the engine is a 2011 L77 6.0 from a Caprice PPV, running an E38 with 12639270 OS. The 4L70e is using a T42 with a 24239036 OS. I'm suspect that the two operating systems aren't going to play together, but this is admittedly an area I know little about. From what I can tell the L77 was never offered in anything with a 4spd and it looks like the current engine OS is the Caprice one, whereas the trans OS appears to be a 07-08 truck OS.

At this point I'm thinking the I should try reflashing the engine as a 07-09 L76 truck w/4spd and going from there, but I don't want to brick anything and I'd prefer not to get into a situation where I'm buying credits to simply experiment with different OS's. Is there any such thing as a database with OS and compatibility info? I'm also unsure what problems I might create elsewhere if I swap the OS.

Any swap guru's have any suggestions as to the best path forward to getting this combo to work?

[blindsquirrel]

There was a change in the ECM-TCM comms protocol between early and late, so you need ECM & TCM OSes to be either both early or both late. Mix an early with a late and no bueno. Note that if you do mix them both modules will talk on the bus and give valid data at the DLC, they just won't know the other module is there because they're speaking code the other doesn't understand.

The ECM hardware also changed in mid-2009, so you can't put an early ECM OS onto your late E38. A 2011 TCM OS is the simplest solution here. Unknown if the Caprice ECM would have issues talking to a truck TCM (of the correct year), might be worth a shot though. T42s programmed to your VIN can be had pretty cheap. It's even cheaper if you can do your own GM SPS flashing.

If this is a swap vehicle with no BCM/SIR/ABS/etc. VIN-mismatch issues to worry about I would keep things simple and use a matching 2011 truck ECM & TCM OS combo. You may have compatibility issues with throttle body & APP if those have already been finalized, showing why planning this stuff out in advance is important!

Gen4 ECMs can only have the OS changed like this properly with GM tools, HPT can only write 6 of the 8 segments. So find a 2011 truck file with a 4 speed, grab the VIN from the tune file, then get ECM+TCM flashed with dealer tools using that VIN. Afterwards copy back in the calibration differences while leaving the new OS and segments in place.

[dzoot]

Thanks so much for the feedback, and for confirming my suspicion that the mismatched OS's are my likely problem.

It is a swap. This is far from my first LS swap, but I don't usually get powertrain packages second hand that are supposed to be "swap ready to go". All of my LS swaps are planned out and all have been successful, but then I usually do everything myself instead of using prepackaged premodified swap setups, so lesson learned there. Unfortunately the car is essentially done, minus this issue, I'd like to avoid reworking for a different T/B or APP, but if I have to I have to.

I have TIS/SPS, no problem there, suggestions for the best combination that may work with the hardware already in the car looks to be my current course. I'll try flashing the TCM with a 2011 file first and cross my fingers.

[blindsquirrel]

1GCNKPEA9BF140932 is a 2011 Silverado, 4.8L & 4L60E. Try that for the TCM-only first, then the whole thing if it has issues.

[dzoot]

An update, Reflashing the TCM with a 2011 year truck 4 speed trans OS does work together with the 2011 PPV OS originally only paired to a 6 speed. At least it works on a most basic level, it will take some road testing still to determine if there are any side effects