alright, i got a killer deal on a 1992 ford f-700 bus ($565) with a 12 valve cummins with a p-pump and allison. Lift pump was bad so i replaced it, and now cant get the fuel system primed again. i took the line off that goes to the tank at the inlet to the lift pump, then i pressurized the fuel tank and got a good stream of fuel @ the lift pump, so i reinstalled the line to the lift pump and tried the hand pump to prime the fuel filter, etc. Then, i cracked the inlet line going into the p-pump and got a decent stream of fuel, then it all turned to air and i cannot get fuel to it again. i worked on this thing for longer than i care to admit and have ran out of patience. ideas?

i figure if i can get my dad to pressurize the tank while i try to prime it that we can get-r-done. but if that dosnt work, what should i do?

P.S. the motor has 155k miles and "supposedly" runs like a top

 

Make sure the pump isn't on the top of the lobe. Try turning the engine over about half a revolution and try priming again, if you haven't already.

 

Replace the OFV = over flow valve , it is what makes the correct fuel pressure , by restricting the return to the tank .
You should be able to get one for about $40-60 , do a search here for Marty Thomkins [ may not have the right spelling ] , Diesel Turbo & injection , Michigan .

 

Was the bus ever hard to start before you replaced the lift pump? If there is any air leak before the lift pump, they are almost impossible to prime.

One of the frustrating things about repriming the system is that if you really have drained it, then the fuel filter and injection pump are full of air. You will have to move a lot of fuel to fill these. I think that you have the right idea about having someone else trying to pressurize the tank and you cracking lines and pumping the primer. That is exactly how I have done it.

Good luck.

 

This sentence indicates to me you must have a leak sucking air inbetween the lift pump and tank.

 

i figure if i can get my dad to pressurize the tank while i try to prime it that we can get-r-done. but if that dosnt work, what should i do?

You can do that and look for the leak that Infidel suspects. Regulate your compressor to 5-8 psi, with a rag and air chuck you can pressurize the tank. If you want to be cleaner, get a extra cap to the tank and install a tire valve in it.

 

stuck a piece of half inch rubber line on the inlet of the lift pump and the other end into a gallon jug of diesel. primed the system and she cracked right off and ran like a top. however it pumps the diesel out of the jug into the tank.... rather quickly too. so i inspected the line from the tank to the pump for holes and found none. Now there was some weird lookin thing thats near the fuel filter, that was the only thing left to try so we bypassed it, filled the line, and it started up and ran great.

anybody know what that thing is?

 

If it has wires running to it it's the fuel heater. They are very well known to leak where the wires enter.
Since you're in the south you don't need the heater, permanently bypass it.
I've never done it myself but understand there is a simple way to eliminate the leaky part of the heater but still retain the housing and the prefilter inside it.
Apparently it's obvious how to do it after taking it apart.