Black dust on left tailpipe

Hi, I was impressed by the help I got for my first topic regarding brake squeal and so I am posting another one. My car is a 2001 996.1 2C 6spd manual. Below are images of my left and right tailpipes. The one on the right is clean and without any dust. The one on the left got cleaned and after some driving it gets this black dust. Some key points: - engine is an original replacement engine (AT designation on the block) and has done about 100.000km - coil packs, spark plugs and AOS were replaced about 20.000km ago - I use the car mostly for weekend driving that involves a 10 minute drive up a twisty country road with lots of 2nd and 3rd gear between 4-6k rpm and I do about 10.000km per year - oil consumption is about 0,5 litres per 1.000km or less when driving at a normal pace - no noticeable smoke at cold/hot start (I got out to check after a few starts since I noticed the dust but found nothing unusual) Is there someone here who had this issue and found a solution?

Possible early stage bore scoring. Best to pull the plugs and sump plate and borescope the cylinders to be sure.

Could just be incomplete combustion. What spark plugs were installed? What brand of coils? Are you running 93 octane fuel? Have you tried running a tank of gas with a bottle of Techron? Oh...and remember left tailpipe is Bank 2, passenger side. There is an oil breather valve on Bank 2 near the AC compressor. Could be leaking.

Quotes source post: 18310651

Assuming the replacement motor is a 3.4L this is almost a non-issue due to different cylinder liners. I'd be more inclined to agree with Joe's thoughts.

Do you have Durametric? Any fault codes stored?

Quotes source posts: 18311205, 18310769

unless the replacement was nikasil cylinders, bore scoring remains an issue with any lokasil cylinder, be it v1 or v2. M96, M97 and 9Ax engines have all seen bore scoring issues. I still stand by my recommendation to borescope. Cheap insurance and easy process of elimination before replacing parts.

Quotes source post: 18311646

How?

Quotes source post: 18310769

I don't have specific information about the coil packs and spark plugs because this was done just before my ownership. They definitely were replaced though. I was using 100 octane when first noticed this, now running 95 octane which is the lowest octane we have in Europe. I haven't used any fuel cleaning agents. Can you show me exactly where this oil breather valve is located? Would the Durametric tool reveal anything useful in case of incomplete combustion? I don't have one but will try to gain access to it or order it. I am not keen on doing bore scoping at this point because scoring or no scoring I wouldn't be able to do anything about it now. Plus the issue seems to be consistent and does not get any better or worse during the last 5.000km I have been following the dust formation.

I believe the common term for that black material is soot. Try searching that word here and you may get some results.

See if u can find the long and short term fuel trims. It may give a clue on combustion. I would also graph the o2 sensors on both side. See if the sendors r "lazy" on that side as this can affect fueling.

I saw your post theother day and thought i would wait for more specific experienced guys who have first hand knowledge of the marque, but from an old mechanic who's experience goes as far back as Carb models that soot in itself wouldn't mean much if it was on both sides, we used to say a light grey soot was normal, darker soot means either rich mixture, meaning fuel air ratio is different on that side versus the other side, or oil burning, that's a very small amount of soot in my opinion, but you also mention you have oil consumption as well. On oil consumption i think that manufacturers seem to have a pretty generous range that says oil consumption is within spec, so your numbers would need to be verified against the manufacturers spec. If you don't want to get the bore scope then don't and drive it and enjoy it assuming it performs well, if you have something going bad it will show up eventually. Personally i don't trust previous owners servicing unless i see the receipts and the shop that did the work has a good reputation, i worked at a dealer back in the 90's here in the USA and saw some mechanics who did crappy stuff to cars. for example maybe changing only half the spark plugs because some were hard to get to, hopefully that's not what happened here. I do think one of the posts suggested checking the fuel trims is a worthwhile option, one bank could be running rich, or maybe an O2 sensor is failing on one side.. Good luck..

I would recommend cleaning both tips extensively. Following this watch the color as some miles are gathered. During this time try to avoid an oil service or using any fuel additives. Watch to see if the soot begins to collect more on left vs right. Performing a boroscope inspection through the oil sump on bank 2 after this would be wise. If scoring is not noted I'd replace the fuel injectors and then clean and monitor the tailpipes again. Doing the boroscope first before the injector R&R will help save some money and hassle if you do have bore scoring beginning. You can do the boroscope inspection yourself using a 50 dollar boroscope from amazon that Jake shows in his Rennvision videos found out youtube

Oil breather valve #6 here http://www.autoatlanta.com/porsche-p...section=104-10

Quotes source post: 18312822

Can you help me locate where #6 connects on the engine?

Quotes source post: 18312892

Hmmm...on the front of Bank 2 right next to the AC compressor. I don't have a picture but maybe someone does.

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

Quotes source post: 18312935

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

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.

Quotes source post: 18313077

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.

Quotes source post: 18312128

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.

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!

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.

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?

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?

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.