I've seen others with similar problems, but those threads seem to have disappeared.

When I run on the front tank, the fuel pump makes a loud humming noise, like it's working very hard to pump fuel. My rear tank had a hole in it, so I ran on the front exclusively for a long time. Now I have a new rear tank.

When I run on the rear tank there is no noise from the pump, but the engine knocks very loud especially when accelerating. It also pumps fuel into the front tank (the front tank does not pump fuel into the rear tank).

I seem to remember someone saying that there is only one fuel pump, not one in each tank. It seems to me that I'm getting less fuel / pressure from the front and that's what the engine is tuned for.

Does anyone know how the fuel system works? It's not in my Haynes. Someone mentioned a faulty check valve or some such as causing fuel to go from one tank to another.

Chris

 

Ford has used at lest 2 different EFI fuel pump systems, not sure which the 94 has.

The older one used 3 fuel pumps, a low pressure pump in each tank and a high pressure pump on the frame rails. There's a recall to add a check valve that prevents the cross pumping of fuel.

The newer system which they implemented as an attempt to solve the cross pumping problem has a separate high fuel delivery module in each tank. Each FDM consists of a pump, suction filter and a pilot-operated check valve. If that valve craps out, then you can still have the crossover problem.

 

Thanks! That's all I needed.

Sadly, the oil pan just cracked / rusted through, so the fuel problem is no longer at the top of my list. Mechanic wants $900 to fix it.