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'90 Ford F150 losing fuel pressure when shut off

I have a 1990 Ford F150, 5-liter V8, fuel injected, with two gas tanks and a tank selector switch. Each tank has its own high-pressure pump. When the car is turned off it loses fuel pressure. To start it, I have to turn the ignition on and let the fuel pump pressurize the system before I crank it. This can take a minute or two before the pump shuts off and it is ready to crank. Before this problem, the fuel system has always maintained pressure when the car was off.



It seems like the fuel is draining out of the system when the car is shut off, since it takes so long to re-pressurize. Any help would be greatly appreciated.

Each fuel pump has an anti-drainback valve. If either of these anti-drainback valves fail, the fuel pressure will bleed off and the fuel in the fuel rails/line will drain back into the tank.

Tester

Thanks for the quick response. That sounds exactly like what is happening. Is there any way for me to check which pump might have the problem, assuming it is just one? Can the anti-drainback valve be replaced individually, or do I have to replace the entire pump assembly?

If you can get at the fuel lines between the two tanks, and have a pair hose pinch off pliers, you can determine whch fuel pump is the culprit. Get the engine started, then go under and pinch off the hose to the tank you’re not running on. Turn the engine off. If you lose fuel pressure, it’s the pump in the tank you were running off. If you don’t lose fuel pressure, it’s the tank that the hose is pinched too.

The valve is part of the pump assembly.

Tester