C7 GrandSport with M7 Z06 gearbox "reduce clutch usage - power reduced" issue

[Sachs]

Hi,

Just finished my transmission swap. (C7 GS with Katech stage 2 cammed engine, 555 WHP)

Updated the ratios in the trans menu. Only first 2 decimals though (original has 4 decimals)

No clutch slip, output trans shaft speed is good. Clutch position is a 0% and no moving when it happens. I calculated the ratios for each gear and I'm finding what I put in the ratios. I don't have any dips in the output trans shaft rpm when it happens.

I probably missed something in the tune... Any ideas ? I doubt me missing some minuscule digits in the gear ratios could cause this problem ?

Got the reduced power and reduce clutch usage message in 1st and 2nd mainly., even at partial throttle.

Alex Katech 03082021 dyna airflow ok idle test.hpt

Log reduce clutch usage.hpl Easy to see when it happens. Timing gets cut like crazy, goes to like -10deg

Thanks for the insight

[Sachs]

Edit : Found the exact ratios with all the decimals : Same issue.

Also got a 5th gear wrong ratio stored in the pcm, lost the gear indicator on the dashboard. Came back after I cleared the code...

Def something related to gear ratios...

Another log :Log reduce clutch usage2.hpl

[cadillactech]

Does it throw any DTCs in any module when it shows the message?

[Sachs]

Does it throw any DTCs in any module when it shows the message?

Nope...nothing stored

When I got the "5th gear wrong ratio" DTC though I also got a "wrong data sent by ECM" DTC.

The more I think about it, the more it looks like HP tuners did not send the ratio change to the ECM... It's like the ECM still "thinks" it has the Z51 ratios... ???

[cadillactech]

Did you try a write entire?

[Sachs]

Did you try a write entire?

I did not. I read that it is not recommended and that there is a risk a briking the ECM ?

Clearly the ECM is not taking the new ratios. I tried this morning putting back Z51 ratio and then Z06 ratios. Exactly the same problem in both cases, which tells me HP tuners does not send the new ratios to the ECM

[Sachs]

Question : until I figure out the issue, is there any way to prevent the engine to go in reduced power mode ?

[Sachs]

Up ! Any ideas ?

I submitted a ticket and a HP Tuners software engineer is going to look at it, issue is that I don't know how long it will be before it is figured out. I know some shops did sequential trans swap and other swaps so there must be a solution somewhere...

[Sachs]

Got it guys. If someone tries the same thing one day. To bypass the fact that table 20090 is not working, i did a segment swap using a M7 Z06 file that had the same OS number than my original tune. I had to swap the engine operation segment and rewrite all the tables so they match my previous tune. Just an issue with the knock sensors I need to figure out.

[cadillactech]

Great info, sorry I couldn't help!

[Sachs]

I spoke too fast. Running the Z06 program creates all short of other issues on the fueling/TPS and some sensors (knock retard sensors are not working anymore)

I'm back to square one...

[Sachs]

I just found a temporary solution : disabling the VSS sensor in the Trans menu and configuring my Driver Demand table in RPM instead of VSS and activating " Use calculated VSS "

It has its caveats though : cruise control does not work anymore since the ECU does not know the vehicule speed...

[LSChev]

Working on a car with the same swap. Running into the same issue. It's throwing a code that says improper signal received from TCM.. but I didn't know these cars had a tcm. Perhaps there is another place that the ratios need to be changed. Did you ever figure out anymore?