So I've dynoed a handful of different year SL55/65s and haven't run into this problem until now. I usually do the custom tuning in 3rd gear since it keeps IATs down and is the gear mostly used on the street. Then make a "power pull" in the 1:1 gear or 4th which reads a slightly higher just for the numbers.

When in dyno mode​​ while using manual trans controls, the transmission is kicking down from 4th gear to 3rd every time. It doesn't matter if we try rolling in slowly, or avoid pushing all the way down to avoid the button at the buttom of the pedal, or start the pull at 4k rpms. I then tried resetting trans adaptions via Star with no change. Also, there's a small dip at at 3,600 RPMs in the torque during each third gear pull. When graphed over speed, that dip occurs at around 63 MPH in 3rd gear.

My only guess is that the TCU tune didn't take and the torque limiter is kicking in during the run thus causing the dip/leveling in power. It's also not allowing full manual mode which is causing the kick down whilst trying to do a 4th gear pull.

Any other suggestions/comments?

2005 ​​​SL55 ​​​
- 77mm clutched pulley
- Belt wrap kit
- 550cc injectors (Bosch EV14 52lb)
- Green air filters
- Eurocharged heat exchanger and CWA100 pump
- Split cooling
- Secondary cats and resonators deleted with x-pipe
- Eurocharged ECU & TCU tune

 

Well, what do the tuners say about it, did you give them a call?

 

I ended up mailing the TCU back to the tuner and just heard back from them today. They said that the TCU tune was indeed still loaded on the module and the software readout was good.

Not sure what else it could be as it seems like it is software/logic programming. I don't think anything related to hardware would cause that?