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  1. #1
    767Driver
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    Carbon Build Up and Direct Injection?

    I read and have heard some of the direct injection engines from BMW (335i)are having some issues regarding carbon building on the intake valves and other components. Is this a common problem among all direct injection engines? My Audi RS 4 is sort of notorious for this issue and the apparent removal of the intake manifold and subsequent cleaning if not done under warranty is quite laborious and therefore expensive. Im contemplating another car,possibly 335i sedan or an A3 both direct injection but am a bit concerned about the long term reliability and service issues with this technology. Is direct injection something to shy away from totally or just with these two automakers?

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    Direct injection is on its way in...not just with

    BMW & Audi. I've read and heard reports, but not many. I've got 26K on my 335i and it runs better than new. I hope it stays that way for a long time. Only time will tell.

    <a href="http://s131.photobucket.com/albums/p315/hoscarnag/roadflypix/?action=viewĄt=335siggy.jpg" target="_blank"><img src="http://i131.photobucket.com/albums/p315/hoscarnag/roadflypix/335siggy.jpg" border="0" alt="Photobucket"></a>
    2008 335i Coupe Alpine PP SP CWP Saddle Heated Seats Comfort Access Sirius iPod PS2s(non-RF!)

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    I don't think this is a question best suited

    for us amateurs. Best might be something like the R&T Tech Q&A section where they seek out experts and get professional answers from people who have seen much more than we have.

  4. #4
    Chris
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    Re: I don't think this is a question best suited

    On Audi/VW cars, the exhaust valves are sodium filled. Deposits are burned off due to the heat of the exhaust and the heat of the valve. This accounts for them not having the same issue as the intake valves. The vapors from the PCV and EGR flow back into the head (for emissions), coating the intake valves with oil and deposits, etc. Since there's no fuel flowing over the valves, the detergents in the gas can't clean the valves off. Which in turn leads to one big mess.

    There hasn't been a surefire way to keep them clean besides cleaning every 10-15k miles. A catch can does help and so does methanol/water injection. They say low SAPS oil/ester based oils work good too, but that's all rumors.

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    floydr
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    GM and Ford also use direct injection

    And you should ask yourself: "Why would carbon build up on a surface that only is exposed to air, which is composed of Nitrogen, Oxygen, and a little CO2 and Argon?"

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    the backs of the Exhaust valves see exposure



    <a href="http://s131.photobucket.com/albums/p315/hoscarnag/roadflypix/?action=viewĄt=335siggy.jpg" target="_blank"><img src="http://i131.photobucket.com/albums/p315/hoscarnag/roadflypix/335siggy.jpg" border="0" alt="Photobucket"></a>
    2008 335i Coupe Alpine PP SP CWP Saddle Heated Seats Comfort Access Sirius iPod PS2s(non-RF!)

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    floydr
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    And so are the backs of valves in non-DI engines


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    yep...that they do



    <a href="http://s131.photobucket.com/albums/p315/hoscarnag/roadflypix/?action=viewĄt=335siggy.jpg" target="_blank"><img src="http://i131.photobucket.com/albums/p315/hoscarnag/roadflypix/335siggy.jpg" border="0" alt="Photobucket"></a>
    2008 335i Coupe Alpine PP SP CWP Saddle Heated Seats Comfort Access Sirius iPod PS2s(non-RF!)

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    Re: GM and Ford also use direct injection

    Unfortunately air is not the only thing the intake valves see. The main culprit is oil vapor from the crank case ventilation that gets put back into the intake track. The vapor contacts the very hot intake valves and forms nasty deposits. Google 'direct injection carbon deposit' and you'll get an idea of how pervasive this is. Most of the action seems to be in the VW/Audi world, probably because they have about a billion 2.0 FSI engines out there. But if you look, it is an issue for everyone who sells a direct injection engine. I think it is going to be a big problem when these engines get some miles on them. I hope BMW has a plan...that doesn't involve owners spending a fortune on a teardown and mechanical cleaning.

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    Re: Carbon Build Up and Direct Injection?

    I have 39,000 on 2007 335i Coup with no problems. I use Chevron 93 octane which contains additives.

    2002 X5 4.4
    2007 335i Coupe
    X5 xDrive35d (Future)
    2004 Mustang Cobra Conv R.I.P.

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