I have 1990 f250 7.3 diesel. The injection pump is leaking. Can someone tell me how hard it is to replace and the sequence to replace. Where is the best source for rebuilt injection pump. Thanks in advance for any help

 

Not sure where you are there, but I think there is an injection shop in McAllen that will treat you right.
removal of the pump ...
Remove air cleaner. Mark and remove the electric lines, throttle linkage, trans linkage (automatic), remove fast idle solenoid. Remove front oil fill neck, inside there is 3 5/16 12 point bolts (need a good 12 pt socket) DONT drop one into front cover !!!
remove fuel lines at injectors and fuel feed line from filter. Remove 9/16 nuts from pump mount (youwill need to make (grind thin) a wrench to remove some of them. Also, if you wish, you can remove the tower bolt on the inner drivers side to make it easier to remove the nut there. The whole thing should come out looking like a huge butterfly.
Installation is reversed, just be careful to line up the dowel on the drive gear to the notch on the pump. That will keep the timing pretty close. There should be strike marks on the new pump mounting flange that will line up with the tower mark. Dont move the lines any further apart than their thickness - top of pump toward passenger side to advance timing. Simply pay attention to the way the lines come off the old pump during reassembly and you should be good to go. Also get a pump install kit, it will have the o rings and caps for the return fuel system. Dont crank on the starter when you are ready to pump fuel and you can leave the injection lines a little loose before you actually fire it up. This lets the lift pump fill the system quicker. Its a little messy, but you can wipe it up. Good luck.