Ok ! Heres what i got if you can help. Its a 90 460 EFI Truck. With gas in the tanks and 2 new in tank fuel pumps. The truck will only start and run if I pore gas into the engine. I tracked it down. The pumps were not pumping. No fire to them,then I started back tracking. To the tank select switch on the dash,to the inretia switch,to the fuel pump relay. No fire. At the fuel relay,It has fire to all the wires going into it,except the one going to the inertia switch,which is dead. So I replaced the fuel pump relay with 2 diffrent new ones,still the same.,no wire on one. So as a experment I used a jumper wire to jump from one of the hot wires to the wire to the interia switch. Bingo fuel pumps pumping. But I know its wrong. But anyway I left it like that and tried cranking the engine,with the fuel pumps running. But still the only way the engine will run is if I pour gas in the engine. And it wont stay running. Any ideas ?? I know earlier models have 3 fuel pumps. 2 in- the tanks and one in-line. I also know EFIs need plenty of fuel pressure. Have not check how much I have,but I know there is some at the injectors because, I pushed the bleeder valve. Looks like a lot. Could it be the fuel regulator on the engine. Or should I try to install a high pressure in line pump in the frame. Has this happen to you ? THANKS !!

 

Check the fuel pressure first. It should be between 35 and 45 lbs with the engine not running. Your relay should have 1 of the small wires Hot and both big ones hot, but only during cranking and running. The ECM will kill power to the small hot wire if the engine is not running. The other small wire is a ground so that when the relay is powered, the ground will allow the relay to close and complete the circuit to the pumps. The ECM may be what makes the ground. Try running a wire from the small one that is not hot to a chassis ground and see if the pumps run. If so, you can check the fuel pressure at this time. Also, Check the ECM fuse, and the 2 black wires that go to the body near the battery. These are the ECM ground wires and if they do not have a good connection, nothing in the electronics will work right.
Jimmy

 

As dumb as it may sound ,check and make sure you hooked the lines up right to the fuel pumps.If you hooked to the return line you will not get fuel.Also you should have power to the pumps with the key in the on position.Try bypassing the rollover switch,orjust tape it in the closed position.Some models also had a fuel filter that is a canister type and it is hidden under the crossmember on the drivers side. Good luck

 

You only get power to the pumps with the key on for about 2 seconds. Then they come back on while cranking and while the engine is running. This prevents a fire hazard if there was a line to bust while the key was on and a hot engine was not running.