I recently had a used motor installed in my 93 300D, the old one was slam wore out. the used motor I had installed worked great BUT I have a clack or knock coming from it at all RPMs. To give you an idea how loud, if I turn the AC on High or crank the radio you can't hear it nor at highway speeds. Acceleration is according to spec, oil pressure pegged at 3 when driving and 1.5 to 2 @ idle when warmed up. Temp is normal. Mileage is as advertised. Starts with a touch of the key. I installed new lifters, no change at all, did a LUBRO MOLY purge of the injectors and pump IAW the instructions, no change, ran on straight Extra Virgin Olive Oil since I had the lines out anyway. No change in the knock noise at all. As I've said I've run this on Dino D, Bio D and VO with no change in performance. I think this motor would run on cat "P" but this noise is bugging the hell outta me.

What else can make this noise? Vacuum pump?

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1993 MB 300D 245K died.