Carbon build up
01-03-2009, 03:11 PM
#1
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Carbon build up
There are several people on this forum who know a crapload more than I do about FSI. I understand the basic principle and the benefits.
Carbon buildup occurs in the intake runners and on the intake valves (as it did in my car in less than 7K miles). At under 9K miles, the problem is back with rough running again when cold. The car is going back on Tuesday for that and DRC clunking (again).
Fuel should not be getting to that area of the engine. The only carbon based products potentially in that area come from the oil breather system.
Purely for my edification, does downshifting and over-run braking push hydrocarbons back past the intake valves? It shouldn't in any measurable way from my experience with other more conventional internal combustion engines, but this is a new beast to me.
Open forum. Your thoughts?
With the years, I have learned I know far less than I would usually like to confess publicly.
Carbon buildup occurs in the intake runners and on the intake valves (as it did in my car in less than 7K miles). At under 9K miles, the problem is back with rough running again when cold. The car is going back on Tuesday for that and DRC clunking (again).
Fuel should not be getting to that area of the engine. The only carbon based products potentially in that area come from the oil breather system.
Purely for my edification, does downshifting and over-run braking push hydrocarbons back past the intake valves? It shouldn't in any measurable way from my experience with other more conventional internal combustion engines, but this is a new beast to me.
Open forum. Your thoughts?
With the years, I have learned I know far less than I would usually like to confess publicly.
01-03-2009, 05:46 PM
#2
Re: Carbon build up
"Fuel should not be getting to that area of the engine."
Actually if fuel was getting into the valves and runners you woud NOT have the problem. Combustion causes carbon to be formed..when the valves open the carbon can get on top of the valves and into the tracts....since the fuel does not come into the intake or shower the valves as its directly injected....the fuel can't keep them cleanER.
I suggest just running the **** out of the engine every now and then to keep it from forming....its called the Italian tune-up in the motorcycle world.
Actually if fuel was getting into the valves and runners you woud NOT have the problem. Combustion causes carbon to be formed..when the valves open the carbon can get on top of the valves and into the tracts....since the fuel does not come into the intake or shower the valves as its directly injected....the fuel can't keep them cleanER.
I suggest just running the **** out of the engine every now and then to keep it from forming....its called the Italian tune-up in the motorcycle world.
01-03-2009, 08:01 PM
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Well I do
run the **** out of it several times every day now. Unlike before when I babied it around, I get it past 8K in two gears at least twice everyday. The problem still comes back.
For whatever reason, the off gassing of hydrocarbons in a fine aerosol that adheres to the intake system seems to be a bigger issue with my engine compared to others. Whether it is an issue with the oil rings and wash down or something else, I am not sure.
FSI prevents the cleaning effect of gasoline.
For whatever reason, the off gassing of hydrocarbons in a fine aerosol that adheres to the intake system seems to be a bigger issue with my engine compared to others. Whether it is an issue with the oil rings and wash down or something else, I am not sure.
FSI prevents the cleaning effect of gasoline.
01-03-2009, 09:11 PM
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Right...
Fuel and fuel additives hydrocarbon byproduct in a non pure burn scenario(varied) is causing the carbon buildup in the intake and on intake valves, IMO.
DI is problematic in that it doesn't allow for a 'rinsing' of the valves, as has been alluded to here.
Oil burnoff is a contributing factor but can't explain these levels so fast. Blaming the oil seems to be a copout because nothing can be done about the other. Don't believe it.
DI is problematic in that it doesn't allow for a 'rinsing' of the valves, as has been alluded to here.
Oil burnoff is a contributing factor but can't explain these levels so fast. Blaming the oil seems to be a copout because nothing can be done about the other. Don't believe it.
01-04-2009, 06:08 AM
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Clarification
No one at Audi is telling me it is oil vapor - that is my bright idea.
All I get from Audi is a shrug and "we don't know why?" Honest, if not helpful.
Help me. How does the combustion by product get back past the intake valve into the runner. The only time the intake valve(s) are open, the combustion chamber should be in vacuum, drawing air into the cylinder. Am I missing something?
I understand the lack of "cleaning" of the intake system without fuel in that area. That makes sense.
If I end up keeping the car, I will have the oil analyzed. As it is now, I have less enthusiasm about keeping it.
All I get from Audi is a shrug and "we don't know why?" Honest, if not helpful.
Help me. How does the combustion by product get back past the intake valve into the runner. The only time the intake valve(s) are open, the combustion chamber should be in vacuum, drawing air into the cylinder. Am I missing something?
I understand the lack of "cleaning" of the intake system without fuel in that area. That makes sense.
If I end up keeping the car, I will have the oil analyzed. As it is now, I have less enthusiasm about keeping it.
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01-04-2009, 06:17 AM
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I haven't
With a car this new, and one with multiple problems still under warranty, I have chosen to not meddle or attempt repairs myself.
This is Audi's problem and I don't want to add substantiation to any claim they may make that I somehow contributed to the problems. I drive it and put Audi approved gas in it and otherwise don't touch it.
It is their job to fix it, not mine.
Products like this work, and I have used similar in the past with more primitive engines (not under warranty).
It is a good idea, and a helpful suggestion (thank you), but not applicable to me give the severity and recurrence of this problem and other concurrent problems with the car.
I need to stay hands off.
This is Audi's problem and I don't want to add substantiation to any claim they may make that I somehow contributed to the problems. I drive it and put Audi approved gas in it and otherwise don't touch it.
It is their job to fix it, not mine.
Products like this work, and I have used similar in the past with more primitive engines (not under warranty).
It is a good idea, and a helpful suggestion (thank you), but not applicable to me give the severity and recurrence of this problem and other concurrent problems with the car.
I need to stay hands off.
01-04-2009, 08:26 AM
#10
Re: Clarification
"The only time the intake valve(s) are open, the combustion chamber should be in vacuum, drawing air into the cylinder. Am I missing something?"
No, there is a small amount of overlap on the valves opening and closing. Thee is a small amount of time where one side is all the way open and the other is just a bit. Plus, you never get ALL of the combustion products out of the chamber before the intake opens.
I really doubt that the oil rings have anything to do with this. What would be interesting is to scrape some of the junk off the valves and intake runners and get that to a lab for a review. Maybe the design of the combustion chamber is to blame, or maybe they need to alter the cam overlap and timing.
I would like to get a used RS4 after prices drop a bit more. But given this issue and the DRC stuff, I think I'll wait till this gets sorted and stick with the S4.
No, there is a small amount of overlap on the valves opening and closing. Thee is a small amount of time where one side is all the way open and the other is just a bit. Plus, you never get ALL of the combustion products out of the chamber before the intake opens.
I really doubt that the oil rings have anything to do with this. What would be interesting is to scrape some of the junk off the valves and intake runners and get that to a lab for a review. Maybe the design of the combustion chamber is to blame, or maybe they need to alter the cam overlap and timing.
I would like to get a used RS4 after prices drop a bit more. But given this issue and the DRC stuff, I think I'll wait till this gets sorted and stick with the S4.