This is a little long winded, but I have a wd45 diesel that is in pretty good original condition. It has the American Bosch PSB pump, that had a broken fuel plunger on it when I bought it. Found another injection pump from a wd45 diesel that was supposed to be working until the head gasket on the engine started leaking coolant. The tractor was parked for a number of years, but I had verified the fuel plunger was not broken or stuck from sitting.

I’m not an injection pump rebuilder but am curious and like to see how things work. I do have a service manual for the pump. The pump needed to be cleaned, so I disassembled nearly everything, put in new governor shaft bearings and a seal. Replaced the sleeve bearing on the pump camshaft and a new seal for the fuel pump shaft.  In the hydraulic head, I also removed the fuel plunger and it seemed to still have a precision fit, but I don’t have a way to measure down to microns of an inch.

Then installed pump back to engine, the injectors were previously cleaned, and pop tested for 2000psi. All new fuel filters were installed also. I left the injectors out so the engine could spin faster to get pump primed. Clear plastic tubing was connected to each injector line so I could see when and if fuel was coming through the lines. Fuel eventually did steadily inject through all 6 lines.

I then connected an injector to one of the lines, but it would not push fuel through the injector. I checked the injector on the pop tester again to verify that it wasn’t stuck for some reason, and it wasn’t. I kept backing the pop pressure down on the injector to see at what point fuel would push through. Eventually it was backed down to less than 500psi and it still wouldn’t push fuel through.

It seems to be pumping a good volume of fuel, but it just won’t build pressure. Any ideas on what to look for before disassembling again? It doesn't seem likely that the fuel plunger and sleeve could be worn so bad that it would build hardly any pressure.

Thanks in advance for your time.