why so much carbon on my 997.2 exhaust tips
#1
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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
#2
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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.
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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.
i find it a little strange - not like Porsche created the dfi engine.
#5
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Because you have a DFI engine!
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#6
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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.
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.
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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.
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#8
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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
Last edited by ADias; 09-03-2011 at 01:50 AM.
#9
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Gary
#10
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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!
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#13
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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.
#14
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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.
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.
#15
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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.