87 tbi, no power to relay question *solved*

[Wesman976]

I have an 87 5.7 tbi, V10 4wd. Had it running good then it stalled. After troubleshooting and bypassing fuel pump relay temporarily, fuel pump turned on and it ran great with the bypass. I think there is something wrong between the ignition and the relay to tell the fuel pump to turn on.

I have replaced tank, sender, fuel pump, all fuses and 30amp breakers, fuel tank switch, fuel pump relay, cap, rotor, module, plugs, wires and much more.

Tbi works great but I’ve lost signal to tell pump to turn on and I’m at a loss. I appreciate anything else I should try. I feel like I’m missing something simple.

Thanks in advance, just trying to get back on the road.

 

[Ricko1966]

There are 3 paths to power for the pump on a TBI truck #1 the ECM turns on the relay to prime the pump, then the ECM breaks that connection and when the truck starts the ECM signals the fuel pump relay to cl8se and stay closed until the ECM shuts it off. There is a backup curcuit that takes 12 volt power through a second oil pressure switch not the same one as for your light or gauge, a second oil pressure switch that provides 12v to the pump as long as the engine has oil pressure. Pics and description of how you are jumping the relay would be helpful. There are wiring schematics in the resource center go to the three dashes upper left,hit that,when that opens scroll to resource center hit that. Scroll to find your wiring harness. If you need help with the schematic,screen shot it and post-it with your questions regarding the circuit.

 

[Ricko1966]

At your relay orange wire terminal #1 should have 12 v with the key on. Does the orange wire have power? The black and white wire terminal F should be ground verify ground with an incandescent test light,not a meter,not an led, connector unplugged test light clipped to battery + touch the probe to black and white at the connector, does it light? Tan and white is power out to the pump,if you provide 12v there does the pump run? The green wire should have 12 volts with the engine running. Does it?

 

[Wesman976]

*solved*

Thanks so much for the advise, I chased my tail looking at the relay again, switching fuses, testing oil switch, disconnecting ecm and testing it…..ultimately I found a loose power wire which was under the truck near the starter, connecting the power to the fuel pump and relay. Reconnected it and “Indiana” (his name) fired right up. Thanks again.