Working on a 1989 f150 with twin tanks started with a motor change and have run on to more problems.Truck had set for two years with the blown up motor so after motor swap siphoned both tanks and added fresh gas.Truck ran great at first drove for about 6 miles total then started sputtering and jerking. Truck seems to be starving for fuel and I had read on the forums about the primer pump in each tank gauge shows full with about seven gallons in each tank. Also read several threads about the problems with the Fuel selector valve had thought of getting one for a single tank and trying one at a time??? Was wondering if it should still run without the primer pump working?? Thoughts Ideas Prayers Thanks.............

 

Have you replaced the fuel filter?

 

Twice........... Today I pressure tested the fuel line 40 with motor off jumping the pump to keep it running. Drops to about 34 when you turn off the pump and then to about 25 in ten minutes or so.Truck will idle and carry about 34-35 after about 5 minutes of running fuel pressure drops to about 20 and it shuts down. Fuel pressure won`t go past 20 after even jumping and running the pump.

 

That *might* just be the fuel pressure regulator.

 

I had thought of that pulled the vacuum line off no fuel there.I know they will leak sometimes when bad. Ran the motor couple times let it idle and revved it up will run for about four minutes then fuel pressure drops shuts off. Wait awhile come back will do the same thing...............

 

It could be that fuel selector valve's o ring swelled shut, but not fully so it lets only a little fuel threw. Pull the Selector valve off and you can take the top off, the oring will be on the outside ring (same outside ring where the screws are removed from). Then you can see if the oring is swollen shut or not. You can take the selector valve apart further, but it's kind of a pain. Lemme see if I can find something that has pictures...

Edit here ya go:

The bolts at the top (I take them out like you put on a tire, one side, then the opposite side, etc.)


Here's with the top off, the o-ring will be in the outer circle, you'll see it:

 

Does the fuel pressure change if you pull the vacuum line off the FPR with it running? I believe it should go up at least 5 psi.

 

Didn`t check that...............

 

Changed out the o-ring seems to have fixed it. THANKS.........

 

Glad to hear it. Make sure that the rear tank isn't filling the front tank, these things do that when the valve get stuck in one position or the other. Mine is currently doing this, and I've tore it down to the valves, yet it still happens. So i dunno if it's fixable.

 

Going to just run on front for now its a money-pit LOL.......

 

Tell me about it, lol. I'm doing everything I can to get better mpgs out of it, timing bump, all new fluids, a hole cut in my airbox, and thermal take around the tubes coming off the throttle body has gotten me a best of 23 mpg. Plans are to get new U-joints, explorer injectors, a high flow cat, and perfect the timing a little better. Hoping for around 27 mpg, high hopes I know lol.

 

There is no "primer" pump. The in-tank pump lifts fuel to the reservoir, and operates the select valve in the DFR. The frame pump raises the pressure & moves the fuel to the injector rail. Both pumps must run for the engine to run reliably. It can run for short periods without the tank pump.That's caused by either the small O-rings (smaller than a pencil eraser) on the valve shafts, or the medium O-rings (dime size) on the valve bodies. Read the DFR captions in this album for more info:

 

On the dime sized o-rings, they don't seem round. they are o shaped, but i mean if i were to cut one in half and look down the rubber it would be square. Would it be ok to use a normal o-ring in place of this?

 

The primer pump I was referring to was the in tank pump. Drove it about 15 miles today and ran fine then started sputtering would idle just no power with a load. Going to change the fuel filter see if it helps.........