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Old 11-09-2011, 12:45 PM   #25 (permalink)
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Das Schlepper Frog - '85 Mercedes Benz 300SD
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Originally Posted by Old Mechanic View Post
I know in the old MB sedans in the early 80s a vacuum leak in the central locking system would allow the engine to run on the air passing through a 1.5 MM ID vacuum line in one of the doors. In 82 they eliminated the throttle butterfly in all of their diesels and claimed a 7% increase in efficiency from eliminating all manifold vacuum completely.


Ahem, the reason why the Mercedes diesel sedans in the late 70s and early 80s would continue to run with a vacuum leak is that they used the vacuum to shut off the engine. A severe leak would drop the vacuum enough it couldn't pull the injector pump to the off position. There was no butterfly valve on the diesels. The diesels had a dedicated vacuum pump. The gains made in 82 were due to an improved cam with more lift that allowed the engines to breath more.