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Originally Posted by Brian Carlton
This cannot be true. If you underboost the engine, you feed it less air and therefore it gets less fuel. It is putting out less horsepower and therefore will produce less heat. You could disconnect the boost line to the ALDA and run the engine without boost and it will run a hell of a lot cooler than it would otherwise run with boost.
If you give it more "throttle", nothing happens. If it is underboosted, no more air is fed to the engine and therefore no more fuel is fed to the engine.
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I believe AusMBtech's point was not that there was no boost, but possibly a condition where there was less than the maximum boost. This would give the driver feedback in the form of the engine needs more fuel to perform as he or she was expecting. The response would then be to push the pedal harder until it hits the floor. This should enrich the mixture for a given rpm, above what that rpm and boost condition would normally demand with the pedal in a condition other than floored. As a result the engine should smoke a bit, or a lot, depending on the conditions. As I understand things, a somewhat or significantly enriched mixture should increase exhaust gas temperatures over a lean mixture in these Diesels. In any case I do not think low boost pressure automatically results in only lean mixtures as I think the driver gets to play a role. On my 240D, without a turbo to complicate things, if I floor the accelerator pedal with the engine turning low rpm under heavy load, I get a good shot of black smoke out the back. I am at a loss to see why this would not be the case with a malfunctioning Alda/boost pressure sensor. Jim
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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles
Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)
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