I have a 1989 F250 with the 7.3 international diesel. After having chronic fuel starvation issues, I pulled the bed and I have replaced everything.

- new mechanical lift pump
- new tank selector valve
- new fuel lines (normal hose with hose clamps!)
- drained and cleaned tanks
- installed clear filters for each tank before the switch
- installed clear filter just before lift pump
- installed check valve just after the tank switch
- new gaskets for tank sending units

After cranking the engine enough to get fuel in it, the engine started right up. I drove it around the yard just fine for a few minutes. Then, I drove it back to my concrete slab where I'm working on it.

It is on a bit of a slant- and the truck is facing uphill. Once it got into this position, the engine faltered and died, just like it was out of fuel- but it isn't. I just poured in 5 gal (front tank). The front clear filter showed that it was not full of fuel like it should be- so it is sucking in air from somewhere. I would think the check valve would help this situation. I think this narrows it down to something before the big filter.

I cranked it and bled the shrader valve on the big filter and got some air out. I cranked it again, and it started, then quickly faltered. It is like it doesn't enjoy pumping up hill (??)

What else could go wrong here? Would it be advisable to install an electric pump just after the tank switch to help out the mechanical pump? Anything wrong with an electric pump always inline feeding the mechanical?

 

replace the fuel/water seperator with a BF1222/ or equivelent from Wix ..... they all leak air at the o ring ..... toss it and get a wix...... no fuel bowl on the wix ....

 

I know you said you put a new sending unit, but I have my old one that has lost the plastic end of the pick up tube, dried and cracked off, and mine does the same at 1/4 tank, which should be about 5 gallons. If you put some more fuel in and problem goes away, then you may have cracked or knocked off the plastic piece off of the pick up tube. IDK just a thought

 

Actually, I have not replaced the sending units- not found suitable ones and don't want to pay the big bux at Ford dealer. On my front tank pickup tube, it has about a 4" length of fuel line stuck on the end. I guess there was supposed to be a plastic extension?

Tomorrow I'm going to put a lot more fuel in there and try again- maybe it was just running out and I have no real problem.

My rear tank pickup doesn't have the fuel hose extension like the front one- I think maybe I'll add one so it sucks a little closer to the bottom, but not so low as to suck up sediment.

 

Ya that's how I tried to fix my front tank when I had that problem and now I can't remember if I put a hose clamp on or not, but mine is still sucking air once I get to a quarter tank. Mine also started dripping fuel out the top till I burn off the first 1/8 tank, been lazy but I think my lock on top is a bit loose. Someday I'll fix it. Good luck.

 

yeah a bit of hose and a cotton sock or a small length of pany hose works good for filters in tank