Since the problem started after the injection (high pressure) pump was rebuilt and re-installed - that is logical place to start looking for an air leak.
- - The idea is that they took something off the engine
and put it back and now you have air leakage somewhere, so it is logical to suspect that area of the engine
- - The fuel
pipes leading to the injection pump sometimes have round copper washers if the attachment is what is known as a Banjo Fitting. These round copper washers are hard to come by so it is common that the installer will try to reuse the old ones. Also a tiny speck of dirt or debris lodged in the washer/gasket of the supply pipes could allow air to leak into the pump.
- - Heating
of the engine will cause parts
to expand and contract
allows air gaps to open up when the engine is cooling
. This will allow air to enter the system. Recheck the bolts/screws holding the parts
of the injection pump together, some may have loosened up a little. Also the "bleeding" screw assemblies might have a speck of dirt preventing them from closing air-tight.
- - If there is an engine mounted "last chance" or CAV fuel filter
the pipes coming into and leaving it are highly suspect for air leaks
as is the filter cartridge itself. There are sometimes little plastic sleeves that slide over the ends of the fuel
supply pipes that split and fracture during removal
and replacement of these pipes. You have to use a flashlight and probe to look inside the hole where the pipes are screwed into the filter to see these little plastic collars.
- - So I suggest starting with the injection pump and inspecting or tighten each fitting/part working back to the lift
pump. Most of these pipes are metal compression
joints which are prone to leak if they are not installed exactly correctly or if some dirt get into the fitting.