Just wanna follow up on this issue.

Car is soon going in for a AH-08 getting new adjusters. Will also change the Variocam adjusters while in there.

I have been working around with the diagnostic a bit with the engine running.

When the car is warm, there is still a pretty noticeable vibration at 1700-1800 rpm.
I have tried to look at the data streams to see where the issue could be, but the only real "error" I can find is misfires on cylinder 4.




However with all new Coils and plugs, I think we can disregard a spark issue.
So its on to looking at fuel injection or air.

Is there a way to verify the fuel injector at that cylinder?

How could I troubleshoot further?

 

So have been working on the misfires in cylinder 8.

New injector installed, and changed spark plug and coil from cylinder 5.

Cylinder 8 is still counting up on misfires. But now Im running out of ideas.
Could it be a cylinder or valve issue?

 

I'd first be looking at the connectors for the injector and the coil on cylinder 8. Look for any sign of damage to the connector and the wiring. There is probably a test procedure that Porsche has for checking the signal there, so it might be time for the dealer. Possible a damaged engine control unit might cause these issues.

After that, it nothing shows up, the next step might be a compression test... followed by a look around with a boroscope.

 

Unfortunately the Cylinder 8 wasnt reachable with the type of Boroscope that I have. So that one hasn't been checked yet.

Im considering a compression test later this week.

Just reading up if carbon build up could make this issue?
Could try a walnut blast to see if that helps.

The engine vibrations are very noticeable at 1700-1800 rpm. Otherwise it is pretty smooth.
Wonder if that is a lead to something? I dont have enough engine experience to troubleshoot misfiring mostly certain rpm's.

 

I have been monitoring the DME datastream the last days. From cold start throughout daily use.

At the cold start, the engine run pretty rough. Misfires on cylinder 5 & 6.
However it calms down eventually. So that is like it was at the beginning of this post.

What have picked my curiosity is the readout from the left bank (5-8) exhaust gas temperature(before CAT). Its all over the scale, and reads from minus to 3700C degrees.
As far as I can see from the parts manual, the Oxygen sensors/Lambda is also the exhaust gas temp sensor.

These erratic temp inputs seems to make a huge difference on the Fuel trim input between the 2 banks.
Bank 2 normally has a mean value difference of 6-7% from bank 1. So this must be where the vibration/misfire issue comes from.
After the engine warms up(quicker in the summer), the vibrations get less, and the misfire counts on cylinder 5-6 stops.
So that rules out that the ignition itself is bad (I think)

From the Icarsoft scanner I do get a diagnostic fault O2 sensor heater.
So it seems like it is the heater part of O2 sensor before CAT on Bank 2 that is broken. The O2 input from the same sensor seems right.


​​​​​​Here are some pictures of the live stream:

 

I'd agree that the heater on bank 2 O2 sensor seems kaput. Question is - is there voltage getting to it (heater itself bad) or not (control circuit problem.) Probably simplest at this point to replace that sensor. They're not terribly expensive..

 

Did some troubleshooting over the weekend.

All the cables between the DME and the sensors beep out good. I did measure the resistance on the heater element on the erratic one vs. the good ones, and they have the same values.
So that is a bit worrisome.

I took the DME out and it looks pretty rough



I took the possibility to clean out the area for old debris and also remove and clean the drain plug.

But just looking at the DME, it is clear that it has been submerged partly in water. The connectors themselves are clean, but the big question is if water has entered the unit, and is causing these erratic readings and engine issues?

I think I will go ahead and remove the left CAT and replace the 2 oxygen sensors and see if things gets better. Its worth a try, and will only cost me half a day and about 150$ (Bosch sensors)

BUT, if it is the DME then it will be interesting indeed.

I have found an exact p/n DME at eBay for around 700$.
Reading through a lot of posts on the Porsche forums, it is clear that Porsche will only reluctantly reprogram a used DME. So its a long shoot.
A new DME is way to expensive.
Unsure if the ECU doctor companies can reprogram a newer ECU like for the 958.

To be updated........

 

Any updates?

 

Not yet.

Car is currently with an Indy dealer in CZ.

We are replacing adjusters (new type), Variocam solenoids and probably the two O2 sensors on the left bank.

Hoping this will solve it.

I also have a vibration at 1200 and 1900 rpm. You can really feel these when stopped and revving, but also during driving. Especially the one at 1200rpm.
So for that issue we are looking at anything up front on the serpentine belt or from the torque converter backwards.

Transfer case will be rebuilt with all new bearings, clutches and chain.

So it will be almost a full overhaul.

Yeah. Did I mention that the ride quality is crap, and height adjustments is intermittent. So we will probably do overhauled struts and airbags on all 4 corners + a new pump.

If this doesn't solve it, it goes out for target practise.