i have a 1990 f250 that i have been driving very regularly but after i drove through a rather large mud puddle it would not start again. i only run on the back tank because my front does not work. it still registers that i have fuel in the tank but no pump. its is a 7.5l 5 speed 4x4. any help much appreciated

 

Did you check to see if the inertia switch was tripped?

 

i popped it back up and then pushed it down again as well

 

there is only one on these trucks correct?

 

Yes, as far as I know.

 

Could it be an ecm or relay?

 

assuming you already diagnosed it as a no fuel issue.....


could definitely be the relay, and is probably the most likely candidate.


the fuel pump test is easy...locate the eec test port under the hood (drivers side fender, on the airbox), and ground the end terminal in the black trapezoid block, its the terminal next to the "loose" single grey connector of the diagnostic cluster. this is to be done with the key on...then you can diagnose your fuel issue. listen for BOTH pumps to kick on, theres an in-line pump on your drivers side frame rail under the cab, and there is a pump in each tank. two pumps run at once in order for your truck to run.


note: I permanently fixed a ground test wire to my firewall, with a male connector that can plug into the diagnostic terminal block, for quick and easy diagnostics when I need it. this will also make pulling codes a breeze, which you should have already done.


now, after you have grounded the fuel pump test terminal with the key on....


-if your pumps do not kick on, its likely a relay issue. look for loose and/or corroded connectors feeding the relay...confirm power to the relay, etc.

-if one pump kicks on and not the other, you likely have a bad pump. less likely, but possible, a bad connection feeding the pump.


-if both pumps kick on, check fuel pressure and confirm that it is ~40 psi.


-if you have 40 psi and you've done all these diagnostics, then you likely didn't confirm it to be fuel at all and you made me write this essay for nothing.


if you haven't confirmed it to be fuel....spray ether (or something else combustable) into the throttle body while cranking and see if it fires. if it doesn't fire, its a spark issue.

 

I have spark and the fuel rail was opened at the test port to check and there was nothing. I replaced the relay, mad sure I had power to the relay and I have no power at the fuel pump connector.

 

did you do the tests I suggested and/or pull the codes? when did you open the test port?


which fuel pump connector is lacking power?


when you do the fuel pump test to ground, youll hear the fuel pump relay kick on. if you hear it, you should hear at least one pump running.

 

I just had these same symptoms and it was my selector switch that went bad on me. Take it off the dash and see if the tabs in the switch are bad. I have a thread going on the first page already. Subford helped a ton. But there are pictures of the procedure to check

 

shryock10,
By the way you do not have a fuel pump on the frame. You have two high pressure pumps, one inside each tank.

Make sure you push down the red button on top of the fuel shut-off switch also called the Inertia switch.
Also check the small black wire with a green or white stripe at the body ground by the battery.

 

Hmmm I thought 1990 was still inline pump....my mistake.

 

Only in the E-series. 1990 was the year the F-series went with the two high pressure pumps in the tanks and 1992 was the year the E-series went with the high pressure pumps in the tank.

 

Only 2 pumps yes. At the rear fuel pump connector I only have 7 volts is this correctt?

 

7 volts with a high impedance meter is no power at that point. You need to use a loading test light to work in this circuit.
The 7 volts is coming from pin #8 of the PCM Computer.

Note that full power will only be on for one second each time the key is turned to the run position.
You need to ground pin #6 of the self-test plug and turn on the key to test this circuit.