Have you noticed any improvement in performance with a full fuel tank versus an almost empty one?

I dismantled the pump and it looked pretty good. The valves were very lightly pitted. I polished the valves and seats with very fine sandpaper. This made a noticable improvement. It will now hold 65 mph. previously it would barely do 60. Will a rebuild kit fix the problem? I plan to install a fuel pressure gauge. Can anyone recommend a good kit?

I installed one in my '82 300D and you would have thought the engine had been overhauled.

I stretched the spring in the relief valve. Performance is inconsistent now. Sometimes it will hold 65; other times it won't do 60. I ordered a fuel pressure gauge today. I'll install it to see if the fuel pressure is indeed the issue. Can the injector pump or governor cause a problem like this? I haven't noticed that the fuel level in the tank makes any difference.

I might be digressing here but have you performed a diesel purge? Dont forget to prime the fuel filter and crack the injectors to bleed it.

Have you cleaned the banjo bolt on the rear of the intake? How is the air filter?

What condition are the fuel lines in?

What style primer pump do you have? The old style can allow air to be pulled in as well.

x2 on primer pump

Just a thought, check your turbo and exhaust to verify there is no pressure build up causing a loss of power.

Also check the rubber connectors of the switch over valve. These do break, and when they do, the boost pressure signal never reaches the ALDA.

I finally installed the pressure gauge. pressure is consistently 28psi and there's no drop when it loses power. How do I tell whether I have the old style primer pump? and what is the ALDA?

I suspect that you might have confused "wastegate controller" with "EGR valve."

I replaced the primer pump; with no results. I'm just about ready to replace the injector pump. What should I have to pay for a good used one?