usually the pump feeds into the bigger line and then it goes to the rail...reg is on the end of the rail with a smaller line coming off as the return....

 

The '87-'89 trucks have a different fuel system than the '90-'96 trucks, as you know. While the '90-'96 have the high pressure pump in the tank, they also have the valve in the tank that prevents fuel from being pumped into the wrong tank. '87-'89 trucks have the dual function reservoir on the frame that prevents fuel from being returned to the wrong tank. This reservoir also holds a small amount of fuel supplied by the low pressure pump. The high pressure pump then takes this fuel from the reservoir and boosts the pressure. I will have to say that the dual function reservoir isn't designed to have high pressure fuel in it and is screwing up the valve inside it which isn't allowing fuel to be returned to either tank.

 

that makes sense to me....

 

Yeah it makes sense to me too, that valve is still availible but it's 160 bucks and only from ford. The guy at napa had another valve that could possibly work but it's still 60 psi max. Anybody have any suggestions?

 

bypass the returns on the valve...run them from the engine to the tank...but then you'd only have one tank...or find a used valve and use just that one for the returns of both tanks...

 

Whatcha mean by that? Ima little confused.

 

I knew you would be...to bad you couldnt get a progressive fuel controller...to set the voltage according to pressure...this would fix it..

instead the the switch dictating where the return goes...you just return it to the tank bypassing the switch...

 

I guess what I'd do is get the fuel line junction block from a '90-'96 truck from the junkyard, and delete the dual function reservoir since you can't use it. It should run right but pump fuel back to both tanks. In a different thread senoirFORDtech posted a picture of some check valves he said would work to keep fuel going back to the proper tank but I don't know how they work.

 

that really makes the most sense to me....

 

How does the fuel system work on the 90 and newer pickups? I looked at our 94 250 with a 5.8 and there is no dual function switch on it. And nothing at the parts store, or even ford matches up with it. The oem valve from ford says it's only a 3 port and mines a 6 port. I dunno, I'm gonna tare that valve apart tmrw and make sure it's even working right.