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Direct Injection - Possible Carbon Build-up Problems Coming?

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It's widely accepted that when a basically all-new engine or component is introduced, there will be teething problems unforseen by the manufacturer until it's used in the real world.

The new Direct Injection engines powering the 997-2 has gotten rid of the intermediate shaft, one of the problems which though hopefully not too common (no official figures released), is still a worry; that should eliminate one source of expensive grief. The DI engine of course will help improve economy and help comply with near-future emissions regulations (or else get legislated out of existence).

However, the direct injection engines so far available from other manufacturers (notably Mitsubishi, VW & Volvo in Europe) have seen a spate of problems with carbon build-up in the valve/head area. I've read two or more comments about that being a common problem of direct injection engines.

Now, I will not profess to be an expert in this so feel free to correct me, but in some articles and blogs I've read, the more common engines (port injected?) make use of the detergent in fuel to keep the valves clean of build-up. DI engines, however, inject fuel directly into the cylinder, so the valve stem areas don't get cleaned by fuel.

I'm hoping that this doesn't end up being one of the problems of this new engine. Any thoughts on the matter?

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The valves in the DFI Cayenne engines stays clean and carbon free in any case, as far as i have seen in a test car with 100.000 Km on the tacho. Since there is no fuel injected on the intake valve stems, only filtered air, there is no deposit or whatever on the stems. There was no abnormal deposit in the combustion room neither.

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That's good, the item I read mentioned something about oil coming from the PCV system hitting the hot head and baking it on, and with fuel not coming in contact with it, is not able to clean it. If such is the case, then I suppose it's really a matter of diligent maintenance and checking/replacing the PCV valve or similar component periodically, if it's what keeps oil from getting in to start with.

Re: the Mercedes 123 diesel (I assume all older diesel engines with mechanical low-pressure injection systems), would they have this PCV valve?

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Re: the Mercedes 123 diesel (I assume all older diesel engines with mechanical low-pressure injection systems), would they have this PCV valve?

If the diesel engine is in a California car, I assume they do.

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  • 3 weeks later...
  • 3 weeks later...

I've seen fuel dilution as a big problem in non-DI engines coupled with long drain intervals in the Boxster, Cayman, and 911, so nothing new here, hence the recommendation for much shorter drain intervals and the need for used oil analysis. Low tension rings, short drives, and fuel enrichment during the warm-up cycle all contribute to this problem.

Edited by cnavarro
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