hey yall, may be a goofy question but my 88f150 has dual tanks, and now that ive replaced half the cooling system so i can let it run, it wont. fuel pressure goes up to 40psi, and within 10 seconds the fuel pressure drops to below 10 and engine stalls. i know i have a frame mounted fuel pump, but im wondering if the fuel system is set up like a diesel, as in a lift pump in the tank and a high pressure pump on the frame. frame pump does work, but is changing that enough or do i need to drop both tanks and replace those pumps also, im assuming it works similar to the diesel trucks in operation but i may be wrong.

 

More likely the crossover valve than both in tank pumps failing at the same time
You can disconnect the lines going into the crossover valve and check the in tank pump output
Those are low pressure pumps in the gas tanks, putting out about 13 lbs into the reservoir / crossover valve assembly
So, check the pump output and possibly do some of the crossover valve checks and repairs in the PCED

 

You should probably change the fuel filter it you haven't already.