How does the tank selector work?

I have a restriction in the return lines on my pickup, and its after where the return hooks to the tank. It holds a steady 20 psi. SO, how to I make it free lowing, and will it mess with the fuel tank selection?

 

The switch on the dash simply sends power to one of the in-tank pumps and there is no other switching hardware to speak of. The fuel delivery module inside the tank contains the pump and a couple check valves, maybe one of those is causing your problem.

 

Yep, I found the valves, and fixed them, but what tells the returned fuel what tank to go to?

 

The check valves inside the tanks do all the directing, I'm not sure exactly how it's done but when a tank isn't energized the check valves stay closed.

 

Hmmmm, ok thanks.

 

Cut from my Ford Service Manual:

The following provides a brief description and function of each of the FDM internal components.

The high pressure fuel pump is located inside the module.

The shuttle selector valve opens the return line to the tank and the return flow is directed to the appropriate tank on vehicles equipped with dual tanks.

The supply check valve, which is normally closed, opens when the outlet pressure from the energized pump exceeds the opposing check valve spring force. When the pump is de-energized (i.e., engine is shut off), the supply check valve closes to maintain pump prime and fuel supply line pressure.

A portion of the high pressure flow from the pump is diverted to operate the venturi jet pump. The venturi pump draws fuel from the tank into the fuel delivery module reservoir to augment the engine return flow. This process ensures an adequate fuel supply to the pump during extreme vehicle maneuvers and steep vehicle attitudes with low-tank fill levels.

The inlet of the venturi pump has a nylon filter on it to prevent dirt and other particulate matter from entering the system. Water in the fuel tank can pass through the filter without restriction.

 

Fuel pressure from the running pump opens its shuttl valve to let the return fuel back in.
Here is a diagram of all of that:
The Fuel Delivery Module (FDM):



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Welllllll, I did a carb swap, so on order to get low enough consistant pressure I had to drill a hole Here



I only did this to one tank, so right now the rear returns to the front tank along with the front. , if I do this mod to the rear tank, I think I will need to adapt shut off valves to the return lines at the tanks to keep the fuel returning to the proper tank, am I thinking right on this?