Injection pump wires and injector torque settings

I think the first thing I'd do is replace the fuel filter. That's usually what causes poor performance with Diesels. Sorry I can't tell you more. Anyone who owns one of these great old machines needs to know a MBZ specialist. Most of the problems are fairly simple. If you want to find a specialist, here's a directory link for you: https://repairpal.com/mercedes-benz-repair-in-phoenix-new-york