I have read on other forums that LPFP's are being replaced first with some success. Haven't had much time to look into this further. But from the pump description the engine oil provides all the lubrication for the moving axial pistons/rotating cylinder. I believe the HP oil (output from the axial pump) is pushing on a diaphragm much like a LP mechanical fuel pump. Although in this case the diaphragm is probably metallic.
Agree it is probably not the diaphragm failing fro the fuel/oil mix reasoning. I don't think that failure or low supply by the LPFP would physically affect the HPFP - other than lack of fuel. From my searching, the axial HPFP's are very propietary as there is not much public info. It would be intereting to tear into one of these and see how they work. Unfortunate that whoever took the photos did not provide any documentation. Although this looks like the oil end of the pump - the cover (which appears to be the fixed swash plate) has an inlet and outlet port. The fuel pressure regulating portion of the pump may be failing. Anyway it is a beautiful afternoon in SoCal and I think I'll go out now and test drive my n54 HPFP to make sure its still working OK.
