Hi
I own a 1990 F-350

I have been working on this truck for at least 3 weekends in a row. this truck once ran for about 5 minutes then quit runing. I dont understand. So I performed a fuel pressure test and came up with 5psi. I know thats way below specs so i decided since i have new parts around the shop i would install them. I installed a new fuel pump relay switch and a new fuel pressure regulator and still the fuel pressure is at 5 psi. Would anyone please help me out with the problem because i do not understand now where to go and both of the fuel pumps are fine they both work properly also I have installed a new fuel filter aswell any ideas please help me thanks Jaeger also I now notice that when resaerching on all data I learned maybe pin connector number 6 from the fuel pump relay and PCM nay not be grounding where do I look to find the location of that wire and color please help me I need thius truck out of my shop Thanks and hoping to hear back Jaeger

 

I had a similar problem with my fuel system. It turned out to be a problem with the fuel pump. Inside the pump there is a diaphram about the size of a dime, it had a small crack in it which made the pressure drop.

Had a garage look at it for two days and they couldn't figure it out. I only figured it out after I replaced the fuel pump, saw it was fixed and then took apart the old pump to see what was wrong.

Moral of the story: you never know if the pump is really OK.

Good luck