6L80E harsh 5-4 power downshift at part throttle

[VE_HTV1900]

Got a weird problem with 5-4 downshift at part throttle with there being what feels like torque converter slip then a bang when it does engage.

I am by no means a tuner but have started looking at the trans tune via a demo version of HPT and comparing other tunes with mine. I noticed that the normal, pattern a & pattern b speeds at 100% TPS do not match with the WOT speeds as they do in the majority of other files I have downloaded. Similarly with the Normal, pattern A, pattern B TCC apply release speeds and TCC WOT apply release speeds. Could this be the (or part of) the problem with this tune?

all the other shifts are ok in comparison.

Any help on this would be greatly appreciated.

[VE_HTV1900]

Guess the overwhelming response indicates turning TM back on...

[abumalik]

Guess the overwhelming response indicates turning TM back on...

I am having the same issue , did you get it fixed , how?

thanks

[Longslyde]

I ran into an issue like this myself. Have you looked at what your Delivered Torque readings were? If the delivered torque was low, the TCM would think you were lighter on the throttle than you actually are and the downshift will initiate slower than what it should actually be. The engine is applying more torque that what the TCM is reading and will not complete the downshift in a timely manner which kinda feels like a shift bind or bang for lack of a better explanation. :/ Adjusting your torque model may very well resolve your problem. Good luck!

[VE_HTV1900]

Took the car back to the original tuners after a full transmission rebuild. They apparently checked whatever it is that is required for calculated torque figures and said it was fine and just did some transmission tuning. Initially seemed better but the more I drove it the more I realised it had just been smoothed out at lower revs/crusing speeds. Back to the new tuner and took the blower off but running a N/A SD tune and it was worse than with the blower on. They sent the Pcm to Melbourne to be wiped and standard GM tune and Os loaded. Now it was changing Sweet as.

Logic was that something got scrambled when the SD OS was applied. The new tuner did his thing with the standard tune and its great...just missing 100 kw. Been a long expensive fuck around.

Buying a manual car to put the blower on....and now know where I won't be taking it in Brisbane regarding tuning.