Fuel problems

[fish]

87 GMC S15, 2.8. We aren't getting fuel, but, the pump works when you hook in up directly to a battery, but does not work when you have it hooked up to the the actual truck wiring, so we are thinking that there is either a bad wire, or a bad relay or something like that.

I checked all the fuses under the dash, but don't see one for a fuel pump. My dad is thinking there should be a relay somewhere but we don't see one for sure that is for a fuel pump.

So I ask, is there a fuse or relay for the fuel pump and where is it located?

[TCossuto]

theres a relay for the fuel pump under the hood. does it RUN with the fuel pump jumped or just pump? Cause if it won't run either it could be your ECM B or A fuse.

[BlazingSaddle]

1.Pull al your fuses one at a time and replace all blown ones with the correct size and rating.
2. Check the ground for the pump at the tank with an ohmmeter.
3. Check for relay operation, should be on firewall, driver side, feel it, it should turn on for 8 or so seconds and run the pump to prime the lines and TBI.
Note here. It wil not run if it just Has. Wait about thirty seconds between tries. Sitting at the ignition switch and expecting it to operate each and every time is not proper testing.
4. If you do find it and it does operate, change it anyway. Considering the nutty problems a funky relay can give you, it's not worth the 8-10 bucks to worry.
5. Once the relay has done its job within the prime part of the circuit, in order for the truck to continue receiving gasoline, the pump will run from a differnt circuit through the oil pressure switch. An oil pressure of 8-10 pounds is neccesary for this path to be good if the switch is working properly. This is a protection ckt should you have an accident. The pump will not continue to run if the oil pressure drops to zero because the engine has stalled. DO NOT circumvent this feature. Bypassing this feature will allow ytour pump to run with the key on and the engine shut off. This may cause fuel to be pumped all over the inside of the motor in the event of a wreck and may lead to a serious fuel fire, with you in the truck.
The timer that turns the prime ckt off is in the puter. The puter switches power to the pump back and forth each time you start your car. yes the fuse to the puter may be bad also, but you've already changed the bad ones, right?

[SY2932]

Quote: Originally Posted by BlazingSaddle

1.Pull al your fuses one at a time and replace all blown ones with the correct size and rating.
2. Check the ground for the pump at the tank with an ohmmeter.
3. Check for relay operation, should be on firewall, driver side, feel it, it should turn on for 8 or so seconds and run the pump to prime the lines and TBI.
Note here. It wil not run if it just Has. Wait about thirty seconds between tries. Sitting at the ignition switch and expecting it to operate each and every time is not proper testing.
4. If you do find it and it does operate, change it anyway. Considering the nutty problems a funky relay can give you, it's not worth the 8-10 bucks to worry.
5. Once the relay has done its job within the prime part of the circuit, in order for the truck to continue receiving gasoline, the pump will run from a differnt circuit through the oil pressure switch. An oil pressure of 8-10 pounds is neccesary for this path to be good if the switch is working properly. This is a protection ckt should you have an accident. The pump will not continue to run if the oil pressure drops to zero because the engine has stalled. DO NOT circumvent this feature. Bypassing this feature will allow ytour pump to run with the key on and the engine shut off. This may cause fuel to be pumped all over the inside of the motor in the event of a wreck and may lead to a serious fuel fire, with you in the truck.
The timer that turns the prime ckt off is in the puter. The puter switches power to the pump back and forth each time you start your car. yes the fuse to the puter may be bad also, but you've already changed the bad ones, right?

That's good advice... Furthermore, the "ECMB" fuse is the fuse that provides power to the fuel pump. If the relay is suspect and you have AC on the truck, the AC relay and fuel pump relay are interchangeable so you can swap them to see if it is the problem or not.