IF you have the OM 603 (six cylinder) and you're hearing it at lower RPM, as you say, 'before boost' - for sake of argument - just above idle but below 1300 RPM, under light throttle? One of the idiosyncrasies of these motors when it has lots of miles. BTW, how many miles are on the engine, timing chain and injectors?

There is a good chance that it's a combination of timing chain elongation and injection timing combined to cause nailing. This can be ruled out by testing the injectors (something that should be done in the neighborhood of every 100K miles.) If they pop at good pressure and spray well, they are not the cause. Do a search for 'injection timing' and 'chain stretch'.

While checking the timing chain, the other possibility of weak lifters can be checked. This engine does NOT have an adjustable valve system BUT there have been forum members, myself included, who put in Mobil 1 turbo diesel truck synthetic 5-W30 and lifter noise has improved. LM Diesel Purge will work for a little while on dirty injectors but if the problem is mechanical no brand of "tool box in a can" will be any more than a quick fix.

Attached Files

chain check.pdf (71.3 KB, 142 views)

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1987 300D (230,000 mi on a #14 head-watching the temp gauge and keeping the ghost in the machine)
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