997.1 turbo Tiptronic guru needed

[niels550]

2007 with 77,000 kms good service history 3 owners, me being the priesent.

Symptom : Gently cruising at say 80-100 kph, take foot off accelerator and coast for say 5 seconds. Put foot back on accelerator to the previous position to maintain the previous cruising speed and there is a loud thunk in the rear which can be felt throughout the car.

Curiously, pulling fuse C1 to take power off the PTM results in a 90% reduction of severity.

All engine, transmission, a diff mounts changed, along with suspension rubbers and the rubber guido which isolates the Cardan shaft.

Now, here's the kicker. I sourced a front drive assembly from a wrecked cabriolet with only 30,000 kms on it. Because, obviously the problem must be in the front drive. Except, it made zero difference.

I then sourced the Tiptronic and torque converter from that same car and swapped them. Zero difference.

So, what's left? Either dodgy ECU, TCU and PTM controllers? Except no codes are thrown. Or dodgy sensor with data that doesn't surprise the TCU or PTM controller?

The car has been at a highly respected Porsche workshop for the last two months while all these bits and pieces were being done.
They're completely stumped and want to wash their hands off it once the original engine and Tiptronic goes back in.

Any and all ideas and suggestions gratefully accepted.

 

[IMI A]

Very strange. Who's your respected Porsche specialist? I'd send to any decent indy or Porsche themselves. Never heard of an unsolvable thunk unless the cars had accident damage and or someones left a tool or bolt in the quarter panel or something stupid whilst repairing. Wheres the wheel nut lock? Hope its not that rolling around somewhere after all that expense? :?

 

[deMort]

You have pretty much ruled out the transmission and i'm guessing the suspension .. you then need to move onto how the box and ptm work .. ie the engine inputs ..

Control units for the PTM/Tip will be suspect until proven ok but in my experience they are pretty reliable .. an incorrect polarity jump start will screw up the tip CU though .. that's a fact .. how did this fault start ? .. any info there ?

Engine inputs .. main one is the maf sensor for engine loading .. you also have the possibility of a partially seized ancillary .. on a tester you look at engine load .. 20 % is a ballpark idle figure .

Hard to say very much as without experiencing the fault i have no idea if this is transmission or something else .. no offence .. but ..

We eliminate the obvious .. whatever we are left with no matter how illogical is the fault .

 

[niels550]

De Mort: To answer your queries.

First, my apologies, your cue to it being an ECU triggered my memory about a vital bit of data I left out.

When I bought this car (sight unseen) it arrived with an aftermarket loud exhaust and big inter coolers. So, the big clue is that in all likelihood the car has been 'tuned". Also, the original exhaust was included. I have since re-I stalled the original exhaust.

But... as part of the transmission swap, the car had to be sent to the Porsche dealer workshop so that the ECU/TCU could be recoded. Also, their PIWIS apparently is able to collect data which is sent to Germany for analysis. Nothing conclusive emerged. I also asked for the ECU to be re-flashed back to standard.

Now the car is back at the Porsche centre for re-coding because the original transmission is being put back in. And I presume, another read of data which will be sent to Germany.

When I get the car back (next week sometime) I will follow up on your suggestions - these make the most sense from any that I've heard of to date.

Will report back!

"”"”-

As an aside, from reading stuff about the PTM online, I understand the PTM clutch disengages when the accelerator pedal is at zero. And obviously re-engages when pedal is depressed.

So, do you think the thunk could be from the cutch engagement being instantaneous rather than being gently fed in?

And purely by way of diagnoses, would wiring in a small soft start bit of circuitry before the PTM be of any use? I gather the PTM clutch is PWM modulated hence, I'm not sure that bit of circuitry would even work.

 

[niels550]

IMI A: Yes, the car is at a P Indie. They've been at it for 30 years. 6 hoists, everyone has a P car on it being worked. They've admitted defeat and sent the car to the Porsche Center for diagnosis. Apparently, there's proprietary stuff that can only be seen by eyes in the factory. I'm guessing, it's the coding. This has been downloaded and sent.

Car has been worked on, looked at, and driven by no fewer than 5 experienced Porsche mechanics. I've done my best to leave no stone unturned when it came to seeking advice and acting on it.

Other than this gremlin, the car is just perfect.

 

[darkhorse]

Are you in the UK out of interest? Im guessing not as you gave mileage in km!

I would consider contacting deejaymarski, he is a boss on turbos and very helpful, you can find him on facebook, he is stateside.

Have you had the ecu and tip control ECU looked at yet to confirm it is stock code on there? With you saying the car seemed to have been tuned, that would be worth checking initially possibly.

Sounds like you have covered a heck of a lot of bases so far.
When you say no fault codes, have they taken live logging of the car in a driving state to replicate the issue and check the logs??

Depends what they are using as to if they can do that