klricks

I think you are confusing the 3/8" supply lines with the 5/16" return line.
You will never have 3/8" connected to a 5/16" line.

Since you are going to bypass the selector valve, you would connect the 3/8" line from the tank pump to the 3/8" line feeding the HP frame pump.
Then connect the two 5/16 lines together.

The 5/16 line is the fuel return from the engine EFI / fuel pressure regulator which routs excess fuel from the engine directly back to the tank.

There are various fuel line splice kits available at auto-parts stores.
In a pinch you could use a piece of rubber 3/8" line and force it over the nylon line and secure with hose clamps. I would not recommend that for long term use. Though that's what I did with the 5/16" return lines and has worked fine for a couple of years now. See details and photos in my web site.

In my case I abandoned much of the nylon line and ran new rubber fuel line to the tank. The rubber line will work just fine on the HP frame pump and tank sender fittings using standard hose clamps but you could get the Ford type splice in connectors if you wish.

luvmy88

Thank you for all the help you have given me on my 88. I did bypass the fuel switch on the dash today and both pumps run with the key on, I even forced the pumps to run by grounding the connector on the self test plug like you showed. Tomorrow I'm going to eliminate the switch valve and see if she'll fire up, tried today but still would not start. Put a timing light on her to make sure I had fire to the plugs, that looked good.

Just call me Sean

iTrader: (1)

It's not just a switching valve, it's a reservior that holds the fuel that the high pressure pump pressurizes. You need to swap it for one from a single tank truck.

klricks

I'm not sure exactly what the purpose of the reservoir part of the Dual Function Reservoir thing is, but I don't think there is any high pressure fuel in the reservoir. The reservoir is between the tanks and HP pump and is pressurized by the low pressure in-tank pumps.

First I heard that a single tank system had a reservoir.

There is a fuel filter in there however. It's supposed to be a lifetime of vehicle filter but I had to replace that filter a couple of times before I got rid the the DFR and put in an electric switching valve.
I also put in some generic in-line fuel filters to take the place of the one in the DFR.

jezter

when I had mine changed to a single tank, there was no extra single reservoir installed... it goes from the sending unit/low pressure pump to the high pressure pump to the fuel filter and then to the engine... from the engine is the overflow/extra fuel line that goes straight back to the tank... I have been running that way for 5 months now with no issues from it after a Ford mechanic of 30+ years repaired my truck... I had a fuel pressure gauge on it the other day to test how things were... I hooked it up and turned the key where the pumps primed the lines and it shot from zero up to 40psi and ready to fire up... so no extra fuel reservoir is really needed...

Just call me Sean

iTrader: (1)

There is not high pressure in the reservoir, the reservoir supplies the fuel to the high pressure pump to pressurize, as I already said. With no reservoir the high pressure pump may have low pressure conditions. Yes, a single tank truck has a single function reservoir, just like a dual tank truck has a dual function reservoir. There is not a fuel filter in there, not on '87 and up. The fuel filter is forward of the high pressure pump. '86 and older does have a fuel filter in there.

It's only been 5 months, give it more time and the high pressure pump should burn out for you. You have to check pressure across the board to see the pressure drops that no reservoir would allow. The factory doesn't put useless parts on vehicles. When you occasionally hear a whining sound coming from underneath the truck, that's the high pressure pump starving for fuel.

luvmy88

Thanks for all the input, ordered a new single tank reservoir today from the Motor Co.

Just call me Sean

iTrader: (1)

The proper way to delete the reservoir would be to use the tank pump assembly from a '90 up, which means you would also delete the frame pump. So everybody knows.

jezter

I believe that most auto part stores should have that adapter you are looking for...

luvmy88

I ended up buying a new single tank fuel pump reservoir, working good now. Thanks!