Ok ! Heres what I got,if you can help. Its a 90 460 EFI Truck with 2 tanks and in-tank fuel pumps both new. The truck will not start,only if I pour gas into the motor,then not for long. I tracked it down to the pumps not working. So I back tracked,new in line fuel filter, to the dash select tank switches,to the inertia switch,to the fuel pump relay. No fire. At the fuel pump relay all the wires going into it have fire,except the wire going to the inertia switch. So I replaced the relay with 2 new ones,still no fire. So just to try I placed a jumper wire across the relay. From one of the hot wires to the dead wire going to the inertia switch. Bingo ! Both in tank fuel pumps started pumping. I know its wrong,but any way while I had it that away. And the fuel pump running,I tried to start the engine again. But still it would only run if I poured gas into it. Then not long. I pushed the bleeder valve on the injectors and fuel comes out,seems like good pressure. I know earlier models had 3 fuel pumps,2 in-tank and one in-line. Should I try putting ain-line high pressure fuel pump,in the frame. Has this ever happen to you ?? Any ideas ??? Thanks !!!

 

Keep your truck original. Here's a wiring diagram.

http://www.cybrrpartspro.com/Chilton.../88286W05L.jpg


Does the red wire going to the fuel relay have power? It is fed from the EEC relay. Also, you could have a wire messed up coming from the distributor. There is a wire that sends pulses to the computer. From these pulses it fires the injectors, and turns the fuel pump relay on(this is a safety feature in case the engine dies).

I just looked it up. The wire with the pulses is dark blue and goes to terminal #56 at the bottom of the diagram.

I also just looked up how to test the #56 wire. You can get an old dwell meter, set it on the 4 cylinder scale, and hook it to the wire and ground. Cranking the engine should give you a 45 degree reading. This means it has pulses.

 

When I hit the link I made above, it goes right to the wiring diagram of your truck. I don't know whats wrong, but here's the front end so you can look it up for yourself.