Stuttgart Auto

Goodmorning everyone,
My name is Marco and together with my father we manage the Stuttgart Auto, a Porsche workshop in Verona (IT).
We have a problem that we can not solve on a 997.1 Carrera S with engine type M97 / 01, and I hope that some of you help us to find the solution. I briefly describe the problem and the attempts we have made to resolve it.

With the engine cold and at low revs 1000-1200 rpm the accelerator is pressed and the car does not accelerates in regular way but "rips" and emits from the exhaust a noise burst due to wrong combustion. When the engine warms up everything works regularly, however randomly on the 6 cylinders, the Durametric diagnosis detects me some failure to ignite, which then eliminates and does not save as a fault code.

To solve the problem we made these attempts:

• replace spark plugs and ignition coils
• replaced air mass meter
• replaced generator and relative wire passing over the engine
• replaced the 6 cylinder intake tappets 1-3 (we had more ignition on these)
• tested the actuators of the variocam command
• replaced engine oil
• checked and excluded the presence of false air aspirations
• replaced the fuel pump relay

At this point we do not know what to think to solve the problem, I hope that some of you can give us what advice.
Thank you in advance and I wish you a good day.

bhvrdr

You did everything I would have done. Going out on a limb did you check the oil separator? If you had a cold start ingesting oil perhaps this would cause your misfires

Stuttgart Auto

Hi bhvrdr, thanks for your advice. I have already replaced the oil separator on other cars when there was excessive white smoke at the exhaust, I will try to do it on this too. I'll let you know my progress.

Petza914

Since it's only having a problem at cold start, it might be a sensor that controls the cold start fuel trims. Does it behave the exact same way if you disconnect the electrical plug from the MAF or is it somehow acting differently in that case? When you first start the car in the morning, does it go into the higher RPM fuel enrichment phase for a little bit where the RPMs are higher than a normal idle, like at 1,200 RPM before dropping back down to 800/900 RPM. If the car behaves the same way with the MAF unplugged and with it plugged in you're not getting the enrichment phase, then you may have a bad wire in the wiring harness portion that goes to the MAF since that's one place temperature info is provided to the DME for fuel trims. I had a broken ground wire in mine which meant the MAF wasn't providing any info to the DME and it would behave like you describe. The other temperature input sensor providing info to the DME is the one for the coolant. I would hook up the durametric and see what kind of live values you're getting for intake air temperature and coolant temperature to see if they're in the correct ranges.

Are you getting any specific fault codes other than the misfire codes ('failure to ignite"). The fact that you're getting misfires on random cylinders means it's something common to more than just one cylinder. Are all the misfires being logged from the same cylinder bank or from both banks - that will be another clue. If they're all from the same bank, then you need to start looking at O2 sensors if they haven't been replaced and cam position sensor for the bank throwing the misfires.

Let us know if any of that helps.

Stuttgart Auto

Hello to all. Sorry if I answer only today, but I was waiting for the oil separators to arrive. I have replaced all three of them and together with them all the corrugated black plastic tubes. Unfortunately, the problem still remains. I tried to replace the throttle valve too, but the problem still remains.
Following the advice of petza914 I checked the values ​​of the various temperatures with durametric and all are correct. I have not checked the electrical connections of the maf (I do it this afternoon), but I think it works well because on durametric its values ​​are good and from the cold machine I always have the enrichment phase.
I would also exclude the lambda because in the real values ​​section the graphs are correct and the oscillation reels correspond.
Not having memorized fault codes, but only ignition failures that are then immediately reset, I think it's a mechanical problem. Check this afternoon
the compressions of the cylinders.

Thanks for your advice, I will update you on what happens

Stuttgart Auto

Goodmorning everyone.
first of all I apologize for updating you just now, but believe me, this machine is driving us crazy.
During the past winter, in addition to the parts I mentioned in the first post, we replaced the fuel pumps, but nothing has changed.

After a long time we convinced the customer to disassemble and disassemble the engine and we found the fifth cylinder with obvious seizing marks. We have overhauled the engine and all worked well for a while.

Subsequently we replaced the actuators for raising the valves and the adjustment of the variocam because with durametric we had seen that they were broken.

Now the machine gives us this idea: with the accelerator pressed steady or accelerating, the machine behaves as if it were being released (or rather as if it were slowing down with the engine brake). I relax the accelerator and we will repeat it and everything works normally.
We have no fault code in the diagnosis. Another thing we have noticed is that the idle speed hand is not perfectly still but has a slight vibration.

Has anyone had any such cases? Do you have any good advice for me?

Thanks in advance