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    Thread: Direct injection causes intake valve buildup?

    1. Member greatfox's Avatar
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      05-19-2009 08:01 PM #36
      Quote, originally posted by Shomegrown »
      Um guys...

      Cam overlap EGR means combution deposits (and unburned fuel) still end up on the valves. Gasoline does matter.

      DI engines inject the gasoline very late in the compression stage. There is no way gas is going backwards into the intake.

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    2. Member Shomegrown's Avatar
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      05-19-2009 09:42 PM #37
      Quote, originally posted by greatfox »

      DI engines inject the gasoline very late in the compression stage. There is no way gas is going backwards into the intake.

      I guess I assumed some here could figure out how internal EGR works.

      Basically during the exhaust stroke, the intake valves are opened early before the exhaust is finished exiting the combustion chamber. This forces dirty exhaust, oil, and unburned gasoline hydrocarbons back up into the intake valves and intake ports.

      It has nothing to do with when fuel is injected into the combustion chamber because EGR function occurs later during the end of the exhaust stroke.

      *edit* - To clarify your other point, the injection event doesn't take place late on gasoline engines. You might be confusing things with diesels which inject after the intake valves are closed and during compression.

      On gasoline direct injection engines, you are spraying while the valves are open which means some spray ends up on the valves. Watch the video.

      http://www.youtube.com/watch?v=qd90yHlmfS4

      http://www.youtube.com/watch?v=73BrXCsbd64





      Modified by Shomegrown at 1:49 AM 5-20-2009


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      05-19-2009 10:03 PM #38
      DISI owners have been addressing this by running an oil catch can with redundant in-line PCV valves along with water or meth injection. It seems to help reduce the build-up in the intake manifold and on the valves, but only time will tell how effective it is.
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    4. Member greatfox's Avatar
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      05-19-2009 10:07 PM #39
      Quote, originally posted by Shomegrown »

      I guess I assumed some here could figure out how internal EGR works.

      Basically during the exhaust stroke, the intake valves are opened early before the exhaust is finished exiting the combustion chamber. This forces dirty exhaust, oil, and unburned gasoline hydrocarbons back up into the intake valves and intake ports.

      It has nothing to do with when fuel is injected into the combustion chamber because EGR function occurs later during the end of the exhaust stroke.

      *edit* - To clarify your other point, the injection event doesn't take place late on gasoline engines. You might be confusing things with diesels which inject after the intake valves are closed and during compression.

      On gasoline direct injection engines, you are spraying while the valves are open which means some spray ends up on the valves. Watch the video.

      http://www.youtube.com/watch?v=qd90yHlmfS4

      http://www.youtube.com/watch?v=73BrXCsbd64

      Modified by Shomegrown at 1:49 AM 5-20-2009

      is the condescending tone really necessary?

      Also, I doubt gas grade has anything to do with the problem. Audi RS4 owners don't cheap out on the type of gas they buy.

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    5. Member Shomegrown's Avatar
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      05-19-2009 10:12 PM #40
      Quote, originally posted by greatfox »

      is the condescending tone really necessary?

      Also, I doubt gas grade has anything to do with the problem. Audi RS4 owners don't cheap out on the type of gas they buy.

      It wasn't meant to be condescending.

      If there's a post with a picture of a blue car and someone says "there's no way that car's blue!"....

      What are you going to say to them?

      I didn't say that was the primary cause. I did say it was a contributing factor. Fuel does contact the backsides of the valves. Fuel with better detergent properties will leave fewer deposits.

      There are a number of factors that cause this issue.


    6. Member adrew's Avatar
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      05-19-2009 10:52 PM #41
      So does this also happen to Atkinson- and Miller-cycle engines?

      Quote, originally posted by Wikipedia »

      In the Miller cycle, the intake valve is left open longer than it would be in an Otto cycle engine. In effect, the compression stroke is two discrete cycles: the initial portion when the intake valve is open and final portion when the intake valve is closed. This two-stage intake stroke creates the so called "fifth" stroke that the Miller cycle introduces. As the piston initially moves upwards in what is traditionally the compression stroke, the charge is partially expelled back out the still-open intake valve. Typically this loss of charge air would result in a loss of power. However, in the Miller cycle, this is compensated for by the use of a supercharger.

      A key aspect of the Miller cycle is that the compression stroke actually starts only after the piston has pushed out this "extra" charge and the intake valve closes. This happens at around 20% to 30% into the compression stroke. In other words, the actual compression occurs in the latter 70% to 80% of the compression stroke. The piston gets the same resulting compression as it would in a standard Otto cycle engine for less work.

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      05-19-2009 11:10 PM #42
      Quote, originally posted by Slickvic »

      Word in the 2.0 FSI forum is that the root cause is from the PCV valve sucking oil into the engine and collecting on hot intake valves.

      This is a total German car sweep FTW (6 cyl + 4 cyl turbo) when this is a known issue in both your cars.


      Modified by fbobberts at 7:12 PM 5-19-2009

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    8. Member s-rocc's Avatar
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      05-20-2009 12:15 AM #43
      Quote, originally posted by greatfox »

      is the condescending tone really necessary?

      Also, I doubt gas grade has anything to do with the problem. Audi RS4 owners don't cheap out on the type of gas they buy.

      psst, you're talking to an enginner who designs engines for a major automobile producing corporation.

      i realize that you know it all, i've seen you in action in the a2 forum, but i'd tend to trust him on this.

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    9. Member NOTORIOUS VR's Avatar
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      05-20-2009 12:27 AM #44
      Quote, originally posted by greatfox »
      Audi RS4 owners don't cheap out on the type of gas they buy.

      LOL... ya ok

      You know how many people I've seen put 87 into high performance cars? Most people don't care at all. I bet you most people think high octane gas is a 'gimmick'

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    10. Member greatfox's Avatar
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      05-20-2009 01:16 AM #45
      Quote, originally posted by s-rocc »

      psst, you're talking to an enginner who designs engines for a major automobile producing corporation.

      i realize that you know it all, i've seen you in action in the a2 forum, but i'd tend to trust him on this.

      He's right, I'm wrong. Is that what you want?

      Regardless of the valve overlap, the problem still exists. And it is widespread. I'm just trying to find the root of it because I'm interested in buying a car with DI.

      P.S. I'm a chemical engineer and as such, I have no trouble understanding and learning the technical aspect of matters like this.

      Quote Originally Posted by iamnotemo View Post
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      05-20-2009 01:30 AM #46
      How about some old school remedies like marvel mystery oil or some type f transmission fluid?


      Modified by Crash6 at 7:02 AM 5-20-2009

    12. Member _GoatPunishment_'s Avatar
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      05-20-2009 02:00 AM #47
      Quote, originally posted by adrew »
      So does this also happen to Atkinson- and Miller-cycle engines?

      As for the Atkinson engine, yes kinda... Because the intake valve is held open on the compression stroke a high volume of air is forced back into the intake. Toyota tried to help this by putting a large surge tank on the manifold. What the surge tank actually does is store oil, unburnt fuel, carbon deposits. When the build up gets high enough the engine will fail to start because it can't burn it. I have not seen buildup on the valves yet.

      That heavy carbon build up on the valves will cause burnt valve issues. Toyota's 3.4L V6 has some issues with carbon buildup on the valves. It's usually known once a valve is burnt bad enough to leak causing misfires. The carbon buildup won't allow the valve to spin and cool. The carbon will actually burn into the valve face.


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