I have a 1990 f250 ford pickup 7.5 liter engine duel tanks i replaced both pumps and line and the relay fuse it will start but wont stay started

You know, sometimes a pump goes bad and needs to be replaced. Have your mechanics test it

if the fuel lines have any rubber fuel lines they could be sucking air. also try replacing the fuel caps, it may not be venting

Does the fuel pump relay come on?

The fuel pump relay and the oil pressure switch as well. The oil pressure switch runs power to the fuel pump when you first start it
When the oil pressure reaches operating range the relay takes over
They are both inexpensive so replace both of these parts to be safe and kill two birds with one stone. If one goes out the other will soon enough

First you'll want to check all your fuses in the interior fuse panel and replace any that are questionable. the fuel pump relay is located under the hood, sometimes mounted on the firewall but usually located in the main fuse box under the hood. After checking the fuses, put your keys in the ignition and turn it to K>O>E>O. Key On Engine Off, and listen to see if you hear the in tank fuel pump start buzzing and then cut off. It doesn't stay on at that point, it's just pressuring up the fuel system preparing to start. It might take a couple of times until you hear it. If you don't hear anything at all, and your fuses are good, Your in tank fuel pump is the more likely the culprit. It's about due for one being that its 13 years old. Merry Christmas.

usually yes there is one main fuel pump. usually located on the drivers side of the engine block down low. Or on the frame rail in that general vicinity depending on what engine you have.

If it isn.t a diesel, the pump is in the gas tank, have to drop the tank to get at it.

Running tank one empty could have picked up **** from the bottom of the tank and clogged the in line filter that feeds the engine. It should be located under the truck on the left inner frame rail around the back of the cab area. Replace it don't try to clean it out it will just clog again. They are not that expensive from the locale parts house. DHR... EX Ford Line Mech

Hey lets try this ! Locate your starter solenoid & look for a yellow wire marked with a "W" . That may be the fusible link for fuel pump. Let me know what you find.

I would start by checking you switch for the tanks to make sure it is working right and if the front tanks fuel pump does not work after you check the switch I would get a 12 volt electrical test light and see if your getting power to the front fuel pump if your getting power to it I would say you have a bad pump . But some times the pump will run but the diaphragm gets weak in them.