Had this happen on an OM615, suddenly sounded pretty bad, was almost in front of an auto parts store. Purchased Chevron injector cleaner in the BLUE bottle put it in and the noise went away quickly to never return.

Who remembers Chevron injector cleaner in a BLUE bottle that could be used on diesels?
.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

though the car has given me a respite, I believe I am going to go ahead and change out the vacuum pump. the car was purchased around 1994 and I KNOW I haven't changed the vacuum pump so probably better to be safe than sorry.

Also check the bushing on the intermediate shaft for excess wear while servicing the vacuum pump.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

since I have never installed a vacuum pump before, quick question: is the bushing on the intermediate shaft you mention on the car or on the pump itself?

This was from a 603 but the principle is the same.

I think he means this assembly:



The pump interfaces with that to pump in and out.

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (116k)
1991 350SD (206k)
1991 300D (228k)
2008 ML320 CDI (199k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (267k)

Past Diesels:
1983 300D (228K), 1985 300D (233K), 1993 300D 2.5T (338k), 1993 300SD (291k)

The bushing is behind the pictured gear and there is another one that guides a shaft that runs perpendicular to the one that gear rides on. The gear has to come out and then you're getting into timing chain and timing issues.

How many miles are on the engine?

Was it well maintained before you got it?

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

there is about 250,000 miles on the car. The car was in excellent condition when purchased although the dealer didn't have any service records available.

Since I've had it I have performed oil changes regularly (I've become a believer in changing the oil more often), fuel filters changed regularly, the timing chain was changed at 150,000 miles, valve adjustments every 15,000 miles, monark injectors, etc.

Old school. Who remembers Rotella DFA? My first w123 loved that stuff.

I have seen Techron for diesels recently.

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (116k)
1991 350SD (206k)
1991 300D (228k)
2008 ML320 CDI (199k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (267k)

Past Diesels:
1983 300D (228K), 1985 300D (233K), 1993 300D 2.5T (338k), 1993 300SD (291k)