1994 Ford F-150 Fuel Pumps

- EEC IV

I have a 1994 Ford F150 XL With a problem I see several people are having but no solution. This is my Fathers truck, owned since new and it sits in the garage quite a bit.

Truck will not start.
It has dual tanks.
With ignition on, engine not running, you can hear the fuel pump running continously. It normally shuts off shortly after turning the key on. (Builds pressure then stops until start or pressure drops)
I switch from front tank to rear, not running with ignition on, both pumps do the same thing, each run continously but vehicle will not start.
While looking under the hood with key on, engine off, the fuel pump did stop. I turn key to start and truck ran fine until I shut it off. Then same thing. Pump runs continously, either front or rear, will not start.

I have replaced fuel pressure regulator thinking it was always open. That did not fix the problem.

I replaced fuel filter. No go.

I have disconneted powertrain Control Relay, key on, pumps stop running, won't start.

I have disconnected Fuel Pump Relay, And PCR, Replaced, No start. (Saw this on a post)

Lastly, CEL is on, jump diagnostic plug, and CEL stays on, does not flash code.

I have been able to get started working the throttle, no power from engine, undrivable.

I have reviewed more postings and found others with the same problem. One suggestion was to change both pumps. "One pump relies on other to work properly". As I understand it, I have two tanks, each with thier own pump. Pressure lines join at fuel line "manifold" inside left frame rail, then into a single fuel filter. I assume a check valve(s) inside the fuel pump keeps fuel from going through when the other pump is on, same for the return fuel lines. Can you explain how one of these fuel pumps (check valves.)Fails that niether pump will build pressure?

I'm stumped, please help.

William