After getting the pulley/tune/tcu treatment a month ago I was experiencing lurching on takeoff and wondered what was wrong thinking that perhaps the ecu/tcu was interacting with the wheel spin limiter in a positive feedback loop.

Here's what it turned out to be. The car now has so much torque and the ecu tune has made the throttle so snappy that the g-force on takeoff was pushing me back in the seat and slightly pulling my foot off the gas pedal without my realizing it. Then I would instinctively give it gas because the car had slowed suddenly (of course!) and it would all happen again. So, my car is suffering from newtonian porpoising :-)

The fix was to move the seat down to get my knees lower and below the knee bolster on the bottom of the dash and to brace my body with my left foot before pushing the fungo. Now, we're having FUN!

Has this happened to others out there?

 

well if that's how you figured it....sounds like you are now really experiencing a "positive feedback loop" now.....;>)

 

You can get the same effect when you do bad launches in a car with a clutch.

 

I wont say that I don't buy your conclusion, but the only time I have ever experienced that which you have described is when an electric kool-aid fueled brainstorm inspired a high school buddy and myself to take the factory seating out of his 1955 Olds 88 and replace it with bean-bag chairs (you think hitting the gas was interesting .... you should have seen what happened when you tried to ease on the brakes : )

In these cars, however, with properly secured seats this seems unlikely. I haven't seen it in either of my SLK32s (with a pulley, tune and TCU) nor have I seen it in my SL55 (with pulley tune and upgraded transmission valvebody).
I would lean more towards your original conclusion of the ESP creating this issue (which is why I have it automatically disabled on both of my SLK32s)

Chris

 

Thanks for the suggestion, I will experiment with the ESP off for a while. I did notice while fixing the curb rash on the rear wheels that the center of the tire treads were worn down to the wear indicator bars even though the inside and outsides of the tires had plenty of tread - an obvious indicator of overinflation. Do General UHPs have a reputation of not hooking up when they get worn like this? As a side note I'm thinking about getting Hankook R-S3s to replace the rears in March(ish). I'm betting that will help a bunch!

 

ok - @180, your mention of clutch and @latemodel21 definitely helped me figure this out.

1. The ESP was coming on frequently even on light throttle. This caused the car to behave like a poor clutch launch
2. The jerking that resulted caused my foot to lift the pedal which worsened matters.
3. I chocked myself more firmly in the seat - and took off with a VERY light throttle - which worked, but sorta defeated the whole point of SRT6

So, I went for a joyride and turned the ESP off. That helped for sure.

Here's what fixed it. I moved the transmission control switch from S to W - The Eurocharged TCU code that is mapped to the W switch position, now, by default lets me treat the transmission as a clutchless manual, letting me decide when to smoothly upshift, while automatically downshifting while slowing for a (for instance) stop light. FINALLY the car feels smooth and agile on takeoff. It is still very easy to spin the tires, but since I'm controlling the shifts I can anticipate the drivetrain response to my inputs rather than reacting to whatever the ESP and autoshifting decides to do and thus creating a bad feedback loop.

The only thing I don't know yet is how the Eurocharged TCU would behave if I didn't upshift the trans in W mode at the redline. Anybody know the answer? I checked the Eurocharged website and they have no documentation on the TCU function/feature mods that I could find. My hope is that the W mode would auto upshift at redline...

The final thing I need to change is the tires to get good rubber to the road.

thanks SOO much for the insights folks!

 

W is a pure manual mode....the EGS (transmission computer), will not shift for you, you must shift yourself or the engine will bounce off the rev limiter.

 

So I tested the Eurocharged TCU program in remapped W mode. It automatically downshifts AND after bucking up my courage to give it a try, discovered that it definitely auto-upshifts at appx 6200 rpm. I couldn't be more pleased Now I drive solely in autostick W mode and love it. With the new kumho 285/35/19 ecsta XS ku36's on the rear, and the EU TCU tune what was formerly a bucking bronco is now a smooth thrill.

 

Great to hear. Although the S mode shouldnt provide such a result. It should just shift as a normal stock auto even when you floor it.
I don thave the EC TCU ...yet....but per stock, I redline mine all the time, that's the only way to hit the on ramp or launch from a red light in a >35mph area. ESP off of course.

I did email Jerry recently during the recent Black Friday Sales re the S/W TCU and he confirmed they could ship me a spare reporgrammed TCU which would be plug and play into my SLK32. I was hoping they were reduced but alas, still $599+$200+shipping(~$100).
I also asked if they had fixed the bouncing off rev limiter issues that 32_Krazy (Steve) and other had reported and included a link to the thread and he said - yes they had.
By the sounds of your experience - it sounds like they've fixed that but there might be another problem in S mode.

Also, you obviously didnt opt for the higher 6,700rpm redline option, and I'm curious if that is still offered together with the redline autoshift protection in W mode (and S for that matter) as you have discovered. I've emailed Jerry to check.

b22b

 

One of the great things with Eurocharged is you can tell them what your modification priorities are and they will deliver a semi-custom engineered solution. To ensure synergy and consistency, I got the 65mm pulley, ECU and TCU tunes done simultaneously. For the outcome goals, I specified 1) Driveability, 2) Durability and 3) Performance in that order. I told them this car would never be raced - so, they delivered what I requested and I am totally happy with the 6,200 rpm redline and that it autoshifts at redline with no bouncing. Even with placing performance last, I can't beeeleeeve how fast it is. This is truly a great car.