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Let's pick on the DFI boys again (because it's fun!)
Just kidding, actually. In all seriousness, what's Porsche's policy or recommended interval for combustion chamber cleaning on the DFI cars? I've had two DFI cars, a BMW and an Audi, and both are customer payable events. The BMW was $600 and the Audi was goodwill because they couldn't figure out what the heck was wrong with it... but I think it woulda been like $900 to $1000.
Since I just had my engine all apart fixing all of my other problems, I was nosing around and noticed that my combustion chambers looked great. However, the car was massively apart in order for me to see them. I'm guessing this is a "while you're in there" kind of event for the DFI cars?
Since we're all going to be buying DFI Porsches at some point if we keep buying newer cars, what's the damage? My next car will either be a newsed Panamera or Cayenne Turbo, so you guys are the guinea pigs
Just kidding, actually. In all seriousness, what's Porsche's policy or recommended interval for combustion chamber cleaning on the DFI cars? I've had two DFI cars, a BMW and an Audi, and both are customer payable events. The BMW was $600 and the Audi was goodwill because they couldn't figure out what the heck was wrong with it... but I think it woulda been like $900 to $1000.
Since I just had my engine all apart fixing all of my other problems, I was nosing around and noticed that my combustion chambers looked great. However, the car was massively apart in order for me to see them. I'm guessing this is a "while you're in there" kind of event for the DFI cars?
Since we're all going to be buying DFI Porsches at some point if we keep buying newer cars, what's the damage? My next car will either be a newsed Panamera or Cayenne Turbo, so you guys are the guinea pigs
The Porsche 9A1 DFI design is different than the DFI design on the BMW and Audi...and there is no Porsche policy or recommended interval for combustion chamber cleaning.
That's odd that you posted this yesterday.
I was contemplating the same thing as I’ve been toying with the idea of selling the 07 for something newer and a .2 was on my list.
In the past I’ve had two DFI BMW’s and you’re right about the carbon build up on the intake valves.
From what I read yesterday, it doesn’t seem to be an issue with Porsche’s design. Some speculate that its due to the flat design.
Mine isn't DFI, but have had issues in the past with carbon buildup on the other marques I mentioned . How is Porsche's different?
See post 9 - I was looking for this photo and someone found it. It was explained to me that spraying fuel on the backside of the valve is a preventative measure. Don't read much about 9A1 carbon build up issues...certainly nothing like what you read on the Audi forums.
It appears to me that carbon build up may not be an issue, IMO. Please correct me if I am wrong.
That's a great photo and a great discussion guys. Direct injection motors inject in 3 different modes, stratified charge (ultra lean burn for cruise), stoich (moderate load) and full power (rapid acceleration and heavy loads) where richer AFR is desired for detonation prevention.
In the stoich/full power modes the fuel is injected on the intake stroke at moderate to high pressures. During stratified/lean burn mode however, fuel is not injected on the intake stroke but rather during the compression stroke.
BMW's direct injection turbo motors (N54/N55) inject fuel direct from the top of the combustion chamber at a 90* angle to the piston and intake valves don't see any fuel coming in at any point in time. Intake valves and ports get extremely gunked up over a period of 25-30k miles. Audi is even worse. Porsche has done something interesting if that diagram is correct but given direct injection sprays directly into the combustion chamber it will have the same issue.
Dzenno@PTF
Last edited by proTUNING Freaks; 06-17-2015 at 05:17 PM.
On the Audis, BMWs and others that have DFI issues, it is generally not in the combustion chamber. The issue is in the intake runners and mostly on the back of the valves. A conventional engine has fuel that sprays the back of the valves keeping them clean and cool. In the DFI cars, obviously that doesn't happen, hence the build up.
I only know this because I REALLY wanted an RS4, but I cannot justify spending 996TT money on a car that will need carbon cleanings every 20K miles.
Here's a vid from one of our BMW N54 (direct injection motor) customers showing some of the carbon buildup and the work involved in cleaning them (this is typically done every 25-30k if you're looking to get the most out of it from the performance point of view)
One thing to keep in mind is that the carbon build-up on the inlet valves in DFI motors is caused primarily by oil contamination from the crankcase breather system, not from oil seepage down the guides. In port injection petrol engines, any oil is washed off the valve backs by the incoming fuel during each induction stroke. In DFI engines (and Diesels) the fuel is injected directly into the combustion chamber, so it never passes over the valves to wash/cool them forming build-up.
Not sure how many have seen this thread but here's a pic from a 997 DFI motor and its intake valves after 26k miles apparently (2010 C2S in this case):
06-15-2015, 03:40 PM
Let's pick on the DFI boys again (because it's fun!)
