Well long story short i sold mine now a good buddy bought a 91 that well has its issues. Known issues are glowplugs either relay or bad gp. Air intrusion somewhere making it loose prime bad to the point of no crank. And the lift pump is leaking fuel something terrible. My question is with the lift pump leaking fuel would that be the reason he gets air into his system cause i see no other fuel leaks anywhere? Also anybody got the write up or tell me in very descriptive detail what and how i need to go about installing his new lift pump he went with another mechanical lift pump so i need some directions. If i recall correctly there was something about getting the mechanical pump lined up correctly or something thats why im asking anyhow thanks for all the help ahead of time.

 

on the new lift pump, you'll notice that the arm that sticks into the engine is shaped like a channel. the smooth side must run on the camshaft. i don't remember if its top or bottom, but be aware of that as you install the pump. with it properly aligned, you'll notice some spring tension working against you as you try to hold the pump straight to the block.
also, when i did mine, i had a helluva time getting the steel line to screw into the pump, so it might help to have the pump only half in place as you connect that line.

i've never heard of a bad lift pump causing it to lose prime, but i guess its possible. i used to have the same pump problem on mine, and it did lose prime, but it was before i changed the return lines, so i can't pinpoint it as the problem. if you still lose prime after changing the pump, you know the routine: return line kit, etc.

the other thing you need to think about is that all that leaking fuel does a lot of damage to every rubber part in the area. that means engine mount, suspension bushings, etc. on mine, engine mount rotted off, but by design it can't move all that far, upper shock bushings disinegrated multiple times, bump-stop broke off, etc. but none of these things failed on the left side of the truck, making the fuel leak appear to be the cause

 

just a quick response and or question with almost the same issue. i have an 89 7.3. runs great once started minus a little rough idle. it has new line kits and no leaks i can find. also i know the GP's or GP controller is bad. issue i'm having if it sets overnight and even if it is 80 degrees outside it takes for ever to crank before it even tries to fire over. question is could the lift pump have a leak on the internal allowing the fuel to go back to the tank?

 

yes this is possible.
however so is having an air leak in the system some other place besides just the return cap's too.

 

The arm of the lift pump rides on the bottom of the cam. When inserting the arm of the lift pump into the opening, tip it down about 20 degrees. When it's all the way in, you should feel it hit before the pump is tipped up enough to start the bolts. You should have to push on the pump to compress the internal spring a bit to get the bolts in...

 

It really only goes in one way, never had a problem before with my lift pumps....

 

lift pumps usually only fail by leaking fuel, or by failing to pump at all. your air intrusion issue is somewhere else.
also note that return lines will often suck air but NOT leak fuel out, making it difficult to find the leak. i've had problems with the return line fitting on the front of the IP leaking, it seems to be my biggest problem

 

If you can see it leaking then that's probably your problem and personally that's why I went electrical (but that is a personal preference) anyway while trying to get it to start check flow at the schrader valve (while cranking)

 

I 've had this same problem. I am also low on power up small hills. I'm changing everthing except the lift pump. Now I mit have to think of that one to. IP on the way. Has anybody used wellman glow plugs. There coming with the pump because I didn't read this site first. Motorcraft are hard to come by here for under $130.oo . Thanks
Chet

 

ok...changed lift pump still takes long time to crank. it did however i believe improve the idle. i guess next are injectors

 

which ones are good again?

 

I have heard pretty decent reviews about dps

 

for glow plugs, MOTORCRAFT ONLY!, all others burn out quickly. for the lift pump, any should work. when you have an air intrusion problem, the symptom is starts for a couple seconds and dies, takes forever to restart. find/fix leaks or replace the lift pump with an electric so it primes without cranking.
i've been told that the IP sucks strong enough that it doesn't need the lift pump if the system stays primed, but as soon as it loses prime, you're dead in the water

 

Also consider this...
These older truck's are bad for leaking or taking air around the top of the gas tank's.
Where the fuel gauge is, there's two pipes coming out of the tank.
One if for feed, and the other is a return (both tanks) they rust out and crack.
There hard to see, but you should be able to get your hand up there and check their condition and see if it's wet.
If it's taking air there, could be a problem also.
Just in case you haven't checked that.
It has to be air tight from the tank up to the pump, if you've eliminated that, then I'd think about the injectors.

 

Instructions say to use an inspection mirror and crank the motor remotely while watching the cam. There's a flat on the cam that should be down when installing the pump, the pump arm rides on the bottom of the cam. That's how I did it and it worked well.