2020 GT A10 Throttle/Transmission Oscillation Issue

[Exploded_Muffin]

[Posted in the Transmission sub-forum. Cross-posting here for better visibility]

Hi fellas,

Having an issue with my car and wondering if anyone can diagnose what's going on.
It's a 10R80 and the car has been supercharged for 9 months now (12,000 miles in that time).
Been purely driven on the street with Michelin PS4S and about 8 dyno pulls in total.

Nothing was changed on the car and the issue started about 3 months ago so ruling out tuning issues.
The throttle oscillates once I shift into 7th gear in the lower RPM range, almost like I'm moving my feet up and down on the throttle pedal.
I'm positive I'm giving it constant throttle and verified that from accelerator pedal position in my logs.
Originally noticed it in just 7th gear but I think I'm starting to notice it in 8th as well.

Any idea what's going on?
Included a video, watch for the behavior in 7th

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[engineermike]

Looks to me more like the torque converter is locking and unlocking. That rpm fluctuation wouldn’t be possible if it were locked up like it should be.

 

[Exploded_Muffin]

Looks to me more like the torque converter is locking and unlocking. That rpm fluctuation wouldn’t be possible if it were locked up like it should be.

Helpful as usual Mike.
If it's the torque converter will just speed up my plans for a built trans and upgraded converter.
Will look into that, thanks

 

[rabid_josh]

Looks to me more like the torque converter is locking and unlocking. That rpm fluctuation wouldn’t be possible if it were locked up like it should be.

this is 100 percent my exact thoughts as well.

 

[Andy13186]

Would that be a tune issue or physical torque converter issue?

 

[rabid_josh]

Would that be a tune issue or physical torque converter issue?

that would require a little further diagnosis, BUT lockup is electronically controlled.

 

[bankyf]

Would that be a tune issue or physical torque converter issue?

I'd lean towards tune issue. That is the expected speed range for lockup to occur and wouldn't be a super common failure on these.

 

[engineermike]

So the weird thing in the tune is that these converters have 3 modes: slip, lock, and unlock. The earlier calibrations only used slip and unlock. The later added lock, but I tried copying the data to mine and the lock function still didn’t work. Anyway, slip means modulated slip near zero. It will control the slip to a small non-zero amount by modulating pressure supplied to the converter clutch. To the driver, slip mode feels locked most of the time. This mode allows them to gain the efficiency of a locked converter, but minimize the trans line pressure needed to achieve it. It’s in slip mode (not unlocked) from 3rd gear on iirc, and it unlocks during all the shifts and immediately goes back to slip. Being that it’s only in 7th (maybe 8th) I tend to lean towards a trans clutch issue since the converter would behave the same in most gears. 7th is also the “weak” gear, as we already know. Does 7th hold at wot?

 

[Exploded_Muffin]

So the weird thing in the tune is that these converters have 3 modes: slip, lock, and unlock. The earlier calibrations only used slip and unlock. The later added lock, but I tried copying the data to mine and the lock function still didn’t work. Anyway, slip means modulated slip near zero. It will control the slip to a small non-zero amount by modulating pressure supplied to the converter clutch. To the driver, slip mode feels locked most of the time. This mode allows them to gain the efficiency of a locked converter, but minimize the trans line pressure needed to achieve it. It’s in slip mode (not unlocked) from 3rd gear on iirc, and it unlocks during all the shifts and immediately goes back to slip. Being that it’s only in 7th (maybe 8th) I tend to lean towards a trans clutch issue since the converter would behave the same in most gears. 7th is also the “weak” gear, as we already know. Does 7th hold at wot?

Can't do a full 7th pull on the street but my dyno sessions were run in 7th gear.
My last pull on 93 was the red curve which was wavy and unlike the others...…almost like the dyno operator was dancing on the throttle.
Leaning towards a mechanical issue as well but will speak to my tuner first before diving into the car

 

[Exploded_Muffin]

Issue is fixed
My tuner sent me an updated tune file and the issue is gone!
Not sure what he updated in the tune but all good
Transmission lives to see another day

Thanks guys for your insights

 

[Cobra046]

My car has the same issue with being supercharged and jerky 7th gear. I’m on the free VMP tune but would like to know who fixed your troubles? Plan on getting a new tune in the spring.

 

[Exploded_Muffin]

My car has the same issue with being supercharged and jerky 7th gear. I’m on the free VMP tune but would like to know who fixed your troubles? Plan on getting a new tune in the spring.

Did your issue start from day one or develop over time?
I'm currently tuned with Palm Beach Dyno

 

[Cobra046]

I didn’t notice it at first but I’m sure it was there all the time. Thanks for the reply.

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