997gt3north

- this was posted up on another car board i follow
- these pics are from a 2008 porsche cayenne turbo (DI engine)
- apparently this is a very common issue
- also showing up on a lot of audi DI engines (rs4 + lots of others)
- now, maybe a gt3 at 8000rpms will fix this issue but you never know



http://i46.photobucket.com/albums/f1...offman_001.jpg
http://i46.photobucket.com/albums/f1...offman_002.jpg
http://i46.photobucket.com/albums/f1...offman_003.jpg

pdobbs

Why would the valves be so covered when DI injects the fuel directly into the combustion chamber?

Targa Tim

I have a 08CTT. How do I know if my CTT has this problem? or is this a real problem at all if so many cars have it??

MarekN

This would be an ideal test case for the V-Power Shell detergent fuels, which are made with exactly this problem in mind.

One question should be answered, are these the exhaust valves or the intake valves? I would guess exhaust valves, but then I would also guess that this specific car doesn´t get driven very hard, because then most of the deposits would have to be burned off.

The answer of this syndrome most likely lies in the characteristics of the fuel and the fact that the DI engines have a varying fuel/air mixture, which does something to the carbon part of the fuel and deposits it on the valve like that.

mooty

i know of two RS4 audi's that had that very issue!

997gt3north

If your ctt is ticking / clicking then this is a sign apparently

eclou

I have an 08 CTT. Hmmm...

FooFighterGT3

My RS4 had this problem (carbon buil-up). It occurred at 50K mile. I used Chevron with Techron exclusively. I was told Shell with V-power and Chevron with Techron would delay the build-up but misfires would be inevitable. It is a flaw in all DI engines.

mooty

^ aint this great? new technology and all.
perhaps that's why 73RS is so $$$$$.
old technology less problem.

ok, just rambling.

axhoaxho

Yes, after hearing all these DFI cabon buildup stories, I'd be concerned of owning a DFI car for long term (especially beyond warranty period.) This is a good thread to read about the DFI carbon build up issue (http://www.bobistheoilguy.com/forums...Number=1325647.)

Regards,

MarekN

This is quite scary when you read into it. Also, for some reason Audi engines use great amounts of oil. I know one person with a 2,4 liter engine in Switzerland who is on his third engine under warranty because the engine uses 1 liter of oil per 1000 km. One of our cars in the company is an Audi A3 1,6 which currently uses 1 liter of oil per 1000 km.
Compare that with my daily BMW 330d which is driven very hard and uses about 1 liter per 15000 km.

The Audi engines are right up there with the Mazda Wankel for oil consumption, which is saying something. Very bad and obnoxious.

TurboCup87

My go to work car is a Mazdaspeed 6, which has a turbo DI engine. People on the Mazda forums are also noting these intake valve and intake manifold carbon build up.

Turbo4ever

Lucky new GT3/RS = GT1 plus manual

ADias

How are those cars driven? are these essentially short trip grocery getters? Are they exercised often to burn up the carbon?

Why is this a DFI problem? I see nothing specific to DFI to cause this, but I may be wrong.

911rox

I'm no mechanic but looking at those pictures, it would seem to be due to the fact that there is no fuel in the intake chamber to help dissolve the oil vapour build up that would be present. In a conventional EFI engine, the fuel is sprayed before the valve and therefore would lubricate and help dissolve oil/carbon on its way through the valve and into the chamber where it is combusted. Harder you drive, more fuel, more build ups removed.

With the DFI engine, no fuel in the intake chamber as its sprayed directly into the cylinder, so you would get oil vapour from the recovery system sitting on the valve, heat from the other side of the valve baking it and in time, carbon build up...