new to the diesel world. started with an older 7.3 idi. it is a 93 non turbo. it has a fuel issue im unable to chase down. i bought it after it had been sitting for a while. the front tank didnt work and it would stall out on the back tank after driving. the water in fuel light would come on shortly after the fuel filter light would come on and she would die. turn it off start it again (after many cycles) and she would start again run for a bit and then die. not knowing how long she sat and the condition of the fuel in the rear cell i decided to start with the front fuel tank. sender rusted through and tank had some rust. so i replaced both. turned it on ran on the back tank and switched to front tank. ran for a bit at idle then died. i disconnected the rear tank from the sending unit to ensue i was drawing good fuel from the new tank. i then changed the fuel filter and water separator. bled the lines and started up again. water in fuel light came back on then fuel filter and died again. so after: new tank, sender, filter/separator im no closer to running. any advice would greatly help!! how do i test the fuel pressure, where do i test at with it having 2 pumps and what kind of pressure should I have?

thanks for your time!!

 

Swap out the transfer pump. At $20, it's cheap and the old one will probably die soon anyway if it isn't dead already... usually they fail with a lot of spraying fuel everywhere.

When you are messing with that, you'll want to replace the rubber hose which attaches that pump to the line which goes to the tank along the frame rail. It's about 6" of hose, in a loop.

I've had two trucks so far where that rubber hose cracked and it started sucking air.

you can also just run a piece of rubber hose from the intake of the lift pump into a bucket/jerry can of fuel, and just run it that way to verify that the issue is pre-lift pump.

If it runs at all, the IP is not the issue. If there is no air in the line, the IP will do /all/ the work if it has to; it can suck fuel straight from the tank, pressurize it, and inject it. If there is any air, though, it won't do it.

Your issue sounds like either that bit of hose down by the transfer pump, one of the lines from there to the switchover valve, or perhaps the switchover valve itself.

You might try just running a direct line from the front tank supply right to the transfer pump; just get a number of feet of rubber hose and run it directly bypassing everything. See how that works and go from there.

 

To add to above, these fuel pumps run between 4-7psi at the filter. Not sure if you have the scraeder valve at the filter head (looks like a tire valve stem). If yours has it, push the valve in after it stalls, fuel should spray out. This is also the best place to test pressure. On mine when the filter light comes on it is because of restriction of fuel, cant suck fuel to the injecton pump. Try running straight from fuel can like stated above, pull hose from mechanical pump and get a piece of hose that will reach from the mechanical pump the fuel can, I guessing it will run fine with that.

 

welcome to FTE.
as the guys already said, you have a lift pump on the engine, not fuel pumps in each tank.
it sounds like you have a bad tank selector switch, and may also be low on fuel. these trucks are known to crack the pickup in the tank and "run out of fuel" while the gauge still shows between 1/4 and 1/2 tank.
so it sounds like your selector switch is bad, and even though it is set for front tank , it is still drawing off the rear tank, which is low enough to be sucking air and running out of fuel .