I'd be careful if you do the Delivery Valve job. It can be messed up. I've experienced it when a pro fixed my om602's o ring (he only changed one and messed the pump up).

Anyways, if you try it, just read up. There's enough info here to make sure you can do it. Just follow the directions. Also remember the torquing procedure on the DV's... It's important.

That said, my 603 (similar engine but one more cyl) had a good lope to it especially hot. I changed the DV o rings and it cleared it right up. It wasn't leaking fuel (visibly) but the IP was taking in air on the plunger's down stroke since the o rings weren't making a good seal. There's obviously no way to 100% verify that but after the repair that's the only thing that makes sense.

That may or may not clear up your problem but for a few hours of work (removing the intake manifold, injection lines, and delivery valves) you could rule this out.

But... again be careful and extra clean or you could take any life the IP has right out of it. The job has to be done right and done carefully.

Hope that helps.... IP's live a long time in these cars. Bosch's inline mechanical pumps are the best ones ever made IMO. Cummins used them in the Dodges from 94-early 98 and they're also lasting a long time. The later stuff from Dodge/Cummins... not quite the case.

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Tom's Imports of Columbia MO Ruined the IP in changing leaky delivery valve O-Rings - Refused to stand behind his work. Mid-MO MB drivers-AVOID Tom's.