two different types of high pressure injector pumps. Without getting into a discussion about the innards, you can break it down to those that self bleed and those that don't. You can tell the difference the first time your fuel filter gets dirty and if the engine just shuts down with very little warning it's the non self bleeding kind. If your engine "hunts" for a while with the RPM's increasing and decreasing for a few minute before the engine quits you have a self bleeder. As an example, my old Volvo you just changed the filter and started cranking. Eventually it would start and off you went. My Perkins 4-108, I could burn out the starter a dozen times and it would never start. It sounds like you have the latter and not the former. It just takes understanding the procedure for your engine. You don't have to pump a bunch of fuel through the bleed valve, just enough to get the air out. I have a dedicated wrench sitting in it's special place just to bleed the injector pump. It sits with the dedicated wrench for the oil plug on the generator and the special tool for the watermaker. It just makes life simpler. I have an electric pump in my system and in the same location as yours. What it does do is push the fuel through the system so that when you open the bleed valve on the injector pump the fuel will flush the air out without having the use the manual pump lever on the mechanical fuel pump. Without the electric pump you would be have to manually pump the air out. When I run the electric pump, even though it won't bleed the injector pump, I can still hear the fuel returning to the tank. I always have to open the bleed screw.