I have a 1990 f250, 5.0, 4x4 that sat for about a year. truck started up and ran fine for about 3 days and I drove it 7 miles or more. now both in tank fuel pumps are not working.The fuel pump on the frame is working,the relays & tank switch are working.
It will start and run when i put gas in the intake but stalls right away, I did drain the gas and put in fresh gas plus a new fuel filter. All the ground straps to the body that I have found check out.
Has anyone seen this before ? Am I over looking something ?
I am thinking that I will have to pull the bed & start looking for bad wires.
Thanks in advance I really appreciate any help

 

Inertia switch maybe?

Mike

 

Purpose is to STOP all fuel pressure.....no power to any fuel pump. Frame-mount pump still running.

Check front/rear tank fuel switch first; if power is not available to it, neither tank pump will run, and if no power to switch, probably wiring from switch all the way back to tank(s) is OK.

impish

 

Okay so I should have a full 12 volts at the switch when the engine is turning over right

 

Tough call for me here; I have a '96, they used a "module" which valved the fuel from the chosen tank, and the selector switch obviously has to tell the module which pump to run, and which sending unit to activate.

Since the frame-mount (I've heard it called a "low-pressure" pump, but dispute that claim), must also turn on by the pump relay being energized by the PCM, I'm assuming the selector switch operates separately of the frame pump.

So, yes, I think you should have 12V. power delivered to the switch whenever the ignition switch is "on"; not only while cranking. Need wiring diagram to be sure.

BTW, do the sending units work normally (gauges)? If so, then the switch is probably OK. Sorry I'm being so evasive.......it's how I get out of tight places!

impish

Edit: If it were up to me, I would use 2 separate pump relays, one or the other chosen by the switch, PCM turns on the relay I pick. No frigging mysterious "modules"! Too damn many of them things already!

 

Had something simular a while back on my 90 E350, 5.8. Tracked it down to a bad fuel pump relay. This is seperate from the inerita switch. Found it outboard of the battery on the rt fender. There were two relays there, one to put power to the fuel pump and the other to the eec module. Both closed when the ign switch put in run.

 

Thanks for all the input, yes the sending units are working when switch from one tank to the other,also both relays on the inner fender are clicking when I turn the key on.
I am getting voltage at the tank switch, I am wonder If there mite be a bad ground or broken wire going back to the pumps?
Hopefully it will stop raining long enough for me to get under it