I have a 91 F-250 5.8L / dual tanks and as I drove
home from work, probably about 30 miles, stopped at gas station to get soda right by my house. Came out and truck won't start!
What? I have fuel. check gauges. 1/4 tank gauge is usually right on my truck. Well u never know? Gassed it up still won't start? Anyways found out FPs weren't coming on. Changed FP relay, still nothing. Both pumps dead? So I take front pump out and test it with separate battery, works fine! Checked electrical connection no power coming in. Had to work next day so just powered the pump with that separate battery with 2 wires tapped into connector, hope I didn't screw anything up by giving it more voltage, ran great to work and back for 5 days. checked inertia switch and getting 6 volts ? and 12 volts then tried bypassing by grounding both wires together still no luck. My gauges work and I can switch tanks while driving with wire leads into batt in bed of truck from fuel pump. I tried jumping pumps with STO connecter fuel pump lead and still don't work. Looked for burnt wires or anything unusual. Also ran my codes on and off and getting 542 (fuel pump circuit failure, "no kiddin" PCM to ground. That PCM Relay next to my FP relay, Icouldn't get my codes or my truck wouldn't run at all if that was bad, right? what about the module itself is that located in cab drivers side left floor
panel and maybe bad ground there or no? Already looked at pin connector no visible damage. Ground wire to starter relay from block is tight but maybe old and corrosive. Could that be the prob? I need help!
TAR

 

Welcome to FTE!
I would check the computer harness very carefully. It may be damaged somewhere shorting the fuel pump control circuit to ground. Also, I would check to make sure that the "extra" pigtail on the negative battery terminal is hooked up and free of corrosion- that is one of the pcm grounds.

 

Thanks Ford_Six, are you talking about the 60 pin connecter harness or the computer itself? I unplugged the 60 pin on drivers side in engine compartment and carefully inspected it and didn't see any damage. I haven't checked the module itself which is left side kick panel? Is there a ground wire coming directly from the module? basicallly 60 which attaches to pin connecter mounted through firewall?? Negative battery post just has a little short wire which is just grounded to bolt on top of radiator -grille- inside top hood area, other end just free wire attached at cable clamp with negative cable. Do you mean harness attchd at starter relay on negative terminal?

 

also , how do I post my original thread in Electrical forum?

 

I recall reading that the EEC will shut down power to the fuel pump if an engine does not start within a short time. On page 319 of my Clymer super Shop Manual, it says at ignition switch START the power relay " in the microprosser" is energized which sends curent to the fuel pump relay. After 1-2 seconds with no engine start the microprocessor times out and cuts off curent to the fuel pump. I am assuming the power relay refered to is the EEC relay. I know there is an EEC relay next to the fuel pump relay on my truck. I replaced it recently. Note - the EEC relay listed for my truck form my ford (NAPA) dealer and Advance did not work. A universal relay from Advance (Sorensen MR12 universal) did and does work.