Both fuel pumps won't come on, on my 91 F-150, 5.8.
My truck ran fine Saturday until I parked it at
home. Went to crank it. But no fuel pump
sounds. Bypassed the innercia switch.
Replaced the relay. No fuel pressure at the
rail. With starting fluid it cranks Right up.
Until the starting fuel is used up.
I found only 7.5 volts on pin #3 coming into
the fuel pump relay. My Haynes Manual
shows a 20 Gage wire having a fusable link
going into the socket. It is thick enough to
be a 10 Gage wire. I am considering running
a new wire as shown in the schematic from
the starter relay with an inline fuse. What
size fuse should be used?
Make sure battery has a full charge and connections all good. If the battery is down, use a charger and get it charged up. The relay diagram is what my database showed. The relay has two sides, the load side, that arm with arrowhead. If you unplug relay use jumper wire between terminals on load side of relay, the line with arrowhead, the pump should run. As you can see, top wire in diagram, on load side is hot all the time and has fusible link. Engine cranking, do you have fuel injector pulse, just curious? Any applicable trouble codes?
That was very helpful. But still not there yet. I ran the 12 gage wire From the solinoid to the fuel pump relay socket with a 15 amp fuse and paper clip jumping the yellow power wire to the green wire with yellow stripe. Which goes to the inertia switch, also bypassed. My Haynes Manual shows it goes to the EEC pin 8. FPM. I turned the key and no pump sounds. So We've byps
So we've bypassed the fusable link, fuel pump relay and inertia switch. I have 12 volts at the relay and inertia switch. But no pump sounds. I'm not sure how to get at the fuel pump connections. Probably need to drop the gas tanks. Could this be the computer? How do I test it?
I am still trying to figure this out. I have been told to check for voltage. I have 12volts at the yellow wire from the solinoid and 12 volts in the red wire. But nothing on the green wire with yellow stripe, even cranking. With a new relay to the fuel pumps.
The computer has to ground, control side of relay, bottom wire, left side of relay in diagram. You see vip test connector, in diagram, ground that wire or use a jumper and ground it. That should energize the relay. Some makes and models it might be possible to have spark at the plugs, but, the computer doesn't see the rpm signal, in that case, no fuel injector pulse and no fuel pump action? You may have to check voltage and ground at the fuel pump itself.
