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Join Date: Sep 2002
Location: Vancouver, BC
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Re: FAQ on Carbon Build-Up Issue (First Attempt)
First, a big vote of thanks for LLcoolM5 for his effort on documenting the problem and what he found when he literally dug into it!
If you think about the way that solid buildup arises, there are a few key points:
- it builds up in the pipe that links the valve and the two cylinder heads. Presumably the heads as well, but certainly the pipe.
- it's a mix of carbon and some sort of binder. Pure carbon is unaffected by xylene or toluene, so for it to slowly dissolve, there must be a "goop" that's actually holding it together.
- the only sources for the carbon and the binder are the fuel and the oil. The S62 runs rich most of the time, and most rich at large throttle openings. This is the most likely time for carbon/goop to be created and available to go into the passages and the cross pipe.
- the carbon/goop mix must get into the cross-pipe when the circumstances are right. It's unlikely that it gets there when the smog pump is running because it would have to flow against the compressed air current from the pump.
- logically, the carbon/goop mix most likely gets into the pipe when the engine is at full (or nearly full) throttle (so that it has exhaust back-pressure behind it) and the engine is warmed up enough that the smog pump is turned off.
- to get into the pipe, it would seem necessary that the flow control valve that cuts off the smog pump and isolates the two arms of the cross pipe would have to leak in order for the carbon/goop to flow into it. Otherwise air pressure in the plumbing held in place by the closed valve would keep it out.
The big question for LLcoolM5 (or Shadowman, or anyone else that's actually taken these things apart) then is "in your opinion and from what you've seen, is it possible that the whole problem is caused by a faulty control valve?"
I'm very interested in this whole issue!