DBJoe996

This will help...pictures https://rennlist.com/forums/996-foru...e-is-this.html

first996

Great, thank you. Question: if this valve is leaking how does it result in black dust forming inside the tailpipe?

DBJoe996

Allows a slight amount of oil into the combustion chambers of Bank 2. Think of a small mist of oil being allowed into the combustion chamber, resulting in an oily soot in the exhaust. Hey, just sharing a possible problem and solution. Beats bore scoring.... After 20 years and a cheap plastic part in the engine bay, could be the cause.

hardtailer

The mechanism/process, if there is one, whereby this leaking fitting could cause soot different from what you describe, as there is no path for oil that is leaking from this fitting into the combustion chamber(s) of bank 2.

This fitting connects the breather hose to the AOS and carries crank case vapours from bank 2 to the AOS. Any oil leaking past this fitting will only soil the engine instead of being fed to the AOS and from there back into the sump.

Theoretically the leaking fitting could cause air (unmetered by the MAF) to enter the crank case and/or venting hose (practically the oil will seal against air entering). It then travels through the AOS and gets fed to the intake effectively leaning the mixture ever so slightly, as it's unmetered air for which the DME cannot adjust the fueling prior to combustion.
After combustion the oxygen sensors would pickup the remaining oxygen in the exhaust gas whereupon the DME adjusts/richens the mixture. However, since the unmetered air enters the air distributer I think it is safe to say that it will affect the mixture on both banks, not just bank 2.
So the short answer is: No, it won't be the cause.

@first996 you should check for vacuum leaks on bank 2 as well as exhaust leaks on bank2.
Don't dismiss a continously lean oxygen sensor signal as a faulty sensor and replace the sensor in vain but instead consider it an indication for an exhaust lead ahead of the sensor through which oxygen enters the exhaust, gets sensed by the sensor and has the DME richen the mixture. The mixture is so rich that it causes soot on the left tail pipe but the oxygen that leaks into the exhaust gas post combustion is still being sensed and the DME richens the mixture to the max which you can identify using Durametric when you know how to interpret the data.
Just post them when you get there.

Thanks for reading the whole post, I hope it is valuable to you to find the cause instead of just changing out parts without knowing whether it will solve your problem.

jdbornem

95 octane is too low in Europe, and the engine is likely pulling timing. EU octane is measured differently than in the US. You should be running EU octane (RON) of 98 or higher.
https://rennlist.com/forums/993-foru...explained.html

I don't know what that means with respect to your soot issue.

Viper1000

Looks like typical carbon build up. Don't sweet it and drive the car. You can do the same to your other car (I assume you have) and you'll fine the same thing. I hate when "porsche experts" tell you it's a million different issues and that you should just sell the car. To much worry causes premature aging! Drive it and enjoy it!

first996

I am revisiting this thread since I recently had a small oil leak and the cause seems to be the spark plug tube (my engine is a 3.4).

Is it possible that a faulty seal on the spark plug tube results in this black residue on the tailpipe?

Does oil get into the cylinder if the spark plug tube seal is faulty?

Thank you for your help.

De Jeeper

No, a spark plug tube will not allow oil in a cyl. Sorry didnt read the whole thread but diagnostics is key here. U may have to check fuel trims, graph o2 performance and see if full injectors r leaking. I would also do a compression check and bore scope to see if u have a cyl issue or a valve issue.

Do u have any stored misfire codes?

first996

I have the durametric and no misfires were stored. An o2 sensing error in the exhaust was stored but after deletion it did not come back, I think i drove a couple thousand kilometers. How do you check fuel injectors?

De Jeeper

What was the o2 code. It may be a clue. To test the injectors u have to pull them and have them tested but at that point u should get them rebuilt or just buy new ones.

See if u can find the short and long term fuel trim values. This may tell us if u have a fueling or maybe a vacuume issue. If the injectors r dumpjng too much fuel then the computer tries to adjust by leaning out the system. If it cant lean it out u can get an o2 code because it sees a value different then what it expects.