first996

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?

jobyt

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

DBJoe996

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.

Billup

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.

hardtailer

Do you have Durametric? Any fault codes stored?

jobyt

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.

hardtailer

How?

first996

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.

ltusler

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

De Jeeper

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.

Gary12000

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..

BRS-LN

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

DBJoe996

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

first996

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

DBJoe996

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