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Thread: Anyone spot the problem?

  1. #1
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    Anyone spot the problem?

    Hello all from across the Atlantic (Scotland)
    I hope you guys are staying safe in these crazy times.
    I posted this problem a couple of years ago on RS246 but never got a resolution and the car has been in hibernation for a while.
    Now with pretty much a lockdown in the UK i have time on my hands and thought i would try again to see if i can solve this.
    Car is 2004 RS6, Viper ECU and TCU remap, decat exhaust.
    Problem is this:

    Drive along in D, 40mph. Apply what i would call 'medium' throttle (not enough to make it change down to 3rd).
    The car accelerates but not smoothly, not exactly lurching but somewhere in between,a kind of stuttering if that makes sense?
    It feels like either a misfire or it can't decide what gear to be in and is fluctuating between 2 gears.
    If i do the same in tiptro which locks it in 4th, problem doesn't show, and I can't seem to replicate it in any other gear/rpm.
    There are no fault codes and i have replaced the coil packs and plugs so i think my misfire theory is out the window.
    From what i can see from the logs the TC always seems to be regulating when this happens but i assume it will be at this speed/rpm?
    I have done lots of VCDS logging files which are in Microsoft Excel format.
    Is there any way of attaching them (presuming anyone is willing to have a look at them!)

    Regards
    Graham


  2. #2
    Registered User hahnmgh63's Avatar
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    While reading I was going to say do some log files until I got to the end. Since you have been logging and I assume you are throwing no misfire codes then I'm leaning towards the tune or something else like a boost leak? Nubcake or Dhall1 probably know right off hand which groups to log for the T. Converter, I'd have to look through my Vagcom which is in Washington state and I'm in Florida for the next 2 months so not much help there. Has the transmission or T.C. ever been replaced? How many miles/Kilometers on it? Without driving it myself I'd have to rely on your opinion on whether it is the drivetrain slipping as you mentioned or something with the Boost. A good solid pull in 3rd or 4th gear while logging would show if the Boost curve is consistent. Maybe a 3, 31, 115 group. That way you see boost, timing, and the O2's for mixture control. It's a start and the logs you've done may already cover this.
    2003 White RS6 2013 Midnight Blue S5
    2013 Daytona RS5 2x944 Turbo's 1974 911 w/'91 3.6ltr motor
    Roy, WA

  3. #3
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    Thanks for the reply.
    I can't really remember a time when the car didn't have this problem.
    Looking back, i may even have bought it like this but initially i didn't notice it as i was using the ample performance a lot of the time.
    As i became aware of it i decided it was the trans (it always gets the blame) so pulled the motor out, got the trans and TC reconditioned, got the turbos reconditioned and replaced lots of pipes, MAF's, N75, DV's etc etc. Basically it got a real good going over.
    Imagine when i put it all back together and the problem was still there!
    I took the car to the trans guy and let him drive it and he assured me it wasn't a mechanical issue and more likely to be software related.
    That's when i started doing lots of logs to try and pinpoint the problem.
    In the logs there are instances where boost suddenly drops to a very low value then pretty much straight away the requested boost goes back to max. It looks like this is the hesitation and it is caused by the TCU asking for torque reduction but i am not good enough with the data to be certain.

  4. #4
    Registered User hahnmgh63's Avatar
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    Makes me wonder if it is an issue with the tune or the ECU. Heard good things about the Viper tune early on, so I wonder if the file could have gotten corrupted? You might try messaging Nubcake, he knows a lot about the ECU's, I'm using one of his tunes for the 6spd conversion. He customizes it by sending you a baseline and then you send him ME7 logs (a lot more info in the ME7 logs than Vagcom) and he reads them and sends you a new tune. I had a few issues (boost leak) so it took me about 6 tunes but now it is wonderful. So much Torque with the 6spd it engages the ESP a lot when wet at higher speeds.
    2003 White RS6 2013 Midnight Blue S5
    2013 Daytona RS5 2x944 Turbo's 1974 911 w/'91 3.6ltr motor
    Roy, WA

  5. #5
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    Cheers mate,
    A lot of what you are talking about (ME7) is way over my head but i will message him and see if he can help.
    Thanks for your help and advice.

  6. #6
    Registered User hahnmgh63's Avatar
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    It was for me too and I was nervous at first but he ran me through a little tutorial and even I did it
    2003 White RS6 2013 Midnight Blue S5
    2013 Daytona RS5 2x944 Turbo's 1974 911 w/'91 3.6ltr motor
    Roy, WA

  7. #7
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    Anyone in your area that can simply lend you a stock ECU controller to run a quick test? That would easily tell it is an issue with the tune.

  8. #8
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    As far as i know, you can't swap the ECU as its coded to the car.
    I may try and get both ECU and TCU put back to standard maps and see what happens.

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