JLHendrix

I have 2300 miles on my C2 and there is noticeable amount of soot on the inside of my exhaust tips. I have seen others on the dealorship lots with this amount of soot even at 1200 miles. What is the explanation for this. I never had this with any of my BMW's or my 964. I am sure it has been covered somewhere in this forum but I have been unable to find anything to explain why this is occuring or whether it is cause for concern. I am aware that there are concerns about DFI and valve gunk but an unsure whether this is really related to what comes out of the exhaust. Thanks, John

Fahrer

The reason there is more soot in the exhaust wth DFI engines ( and my 2008 BMW 535 has DFI and soot also ) is that some of the fuel droplets injected into the combustiuon chamber hit the piston before beint absorbed into the air. These droplets undergo a somewhat different combustion reaction than the dissolved ( in air) fuel undergoes. This produces carbonized particles, most of which are expelled through the exhaust. Some of it ends up in your motor oil. The sludge buildup is from crankcase fuemes that are normally routed into the intake area. This oily air/blowby can deposit gunk on the intake area of the hea including vales. With port injected engines, the detergent in the fuel normally washes away these deposits. With DFI engines this gunk can build up. The oily depostis might be reduced with better control of the crankcase fumes but, in the end, cleaning out the intake are is the big tune up of the future for these cars. There was a big problem with tthis in erly Audi/VW DFI engines but they have improved the PCV valves on those cars.

JLHendrix

Thanks Driver for a very cogent explanation. I guess the longer term implications of this particular DFI system remain to be determined.
John

Cpa4S

it also ends up building up on the whole back end unless you wash it often. my Cayenne GTS has not had this with the dfi engine.

i find it a little strange - not like Porsche created the dfi engine.

alexb76

Because you have a DFI engine!

alexb76

Great exaplanation...

Have you heard of any solution, or maintenance to clean this up? I assume it will have some impact on performance after a lot of build up.

Fahrer

It is not the end of the world. You can get the intake area cleaned up but to do a good job it might involve removing the intake manifold, depending on the severity.

ADias

It sounds like you are driving short trips and not hard enough. My 997.2 S DFI has no more soot than in my other port injected cars, perhaps even less.

simsgw

Nah, it's not worth spending money on the R&D. After we worked on them for the first seventy years we decided to let guys on forums figure it all out. Easier to take their word for it than to do the engineering.

Gary

Fahrer

Here you go....

http://api.viglink.com/api/click?for...13150570073281

I forgot this one ...

http://api.viglink.com/api/click?for...13150571897181

It is an issue and the industry is trying to deal with it. OEMs are commited to DFI as there are advantages in emissions, power and fuel economy but there are definitely problems that have not been fully worked out. By the way, Engineers are always making compromises!

JLHendrix

Fahrer, you get an A.

ADias

ADias

Not an A. A comment to Post #2: The so called intake valve gunk is soft and is not a combustion product. Easy to remove, if necessary using a Top Engine Cleaner. This has been discussed here forever but it always comes back, even when when there are plenty of high-miles DFI 9A1 engines running around without issues.

Fahrer

I think you are getting some of the comments a bit mixed up here. The soot in/on the tailpipes is combustion product. As I said, the fumes from the crankcase are what end up in the intake area of the head. Yes, and as with Diesels sopme of the soot from the combustion ends up in the crankcase.

I do not care if it is a VW, BMW or Porsche, or other...... soot and intake deposits will be in an issue with DFI engine and the auto industry knows this.

JLHendrix

Fahrer's brief essay regarding the causes of soot on exhaust tips is concise and well supported. Since that was the assignment, his grade remains an A.