I just put a 7.3 idi in my 86 f250 and used the injection pump off my 6.9 because i was told the injection pump was bad on the 7.3 i bought . I put a injector oring and return line kit on . Cracked all the injectors and got it to start after alot of cranking . So next day went to go start it and had to crank it for 2 minutes until it started. When warm it still takes a little to start . Compression tested all cylinders and had 450-500 in each. So i figured it was just losing fuel pressure , i went over everything on the fuel system and no leaks. The only thing is the steel return line has a crimp in it , not leaking . I just installed an electric fuel pump wired to a switch to help prime the system, that didnt seem to help. But if ths block heater is plugged in it starts up after 40 sec of cranking. No glow plugs used . I have a manual switch bypassed the controller. Any ideas what could be wrong ? After my electric fuel pump test , im starting to think its not the fuel system..