Fuel Pump or Electrical Issue

[Dick Altman]

Trying to get my '91 pickup (2 wheel drive and 4 cyl.) I just acquired to run. Will momentarily start if I put gas directly into the fuel injection system. Seems to be a fuel pump or possibly an electrical issue related to it. I hear no noise coming from the pump. Disconnected wires to it and the voltage constantly fluctuates between 1 to 8 volts with key in "ON" position. Shouldn't it be a steady 12-14? There is a connector under the passengers seat related to it. At that junction I get the same fluctuation in voltage. Thoughts and thanks!

 

[tbplus10]

Yes should be a steady 12 - 14.
Check the grounds at the fuse box/powr distribution buss.

 

[Dick Altman]

Thanks tbplus10. You mention "grounds" in the plural. So I assume I'm looking for more than one wire grounded to the chassis? Are these simply wires under the hood near or at the fuse box/power distribution buss bolted to the chassis which I would check for good contact and tightness?

 

[tbplus10]

You should find grounds coming from the power distribution/fuse box to the body, it might be a wire or it might be braided wire straps, either way they'll be attached to the inner fender or firewall with a screw.
Make sure the attaching points are are clean and corrosion free and ensure the wires or straps themselves arent corroded.
If my memory is correct your truck also has a relay type power buss for the fuel pump, make sure its not partially burnt and has clean contact points where it plugs in.

 

[Dick Altman]

Do u know where that's located? And by "buss" do you mean fuse?

 

[tbplus10]

You should have an underhood fuse box that its located in.
Yes the buss will be like a larger fuse, normally sized about 1"x1" and 1 1/2" deep, could possibly have a clear plastic top to see the fuse inside.

 

[Dick Altman]

I don't have wiring diagrams yet (awaiting Factory Service Manuals). I don't know where the relay buss for the fuel pump is (the lid of the fuse box on the left side of the engine compartment does not list "fuel pump" though it does list "EFI" etc.

Tracing the wire from the negative terminal on the battery nothing from it goes to the "power distribution/fuse box". This is what I would expect. I would think that only circuits from the positive terminal on the battery would go into that box. But maybe I'm wrong or maybe I'm not understanding you. In tracing the wire from the negative battery terminal, one branches off and is bolted to the side of the engine compartment (see picture). Another branches off and attaches to the frame underneath.

I disconnected the wire bolted to the left side of the engine compartment and cleaned it though it looked to be in good shape. Tested voltage at junction in the cab (see picture - yellow with red tracer and brown with blue tracer) with no change. The voltage still fluctuates wildly.) AM I TOUCHING MY PROBES TO THE CORRECT TWO WIRES?
Maybe I have a bad connection on the buss fuse connection dedicated to the fuel pump. But I just don't know where it's located to be able to check it out without a wiring diagram or advice.

Would a defective electronic module be responsible for the voltage fluctuation?

Please take a look at the pictures of the wires inside the cab. You'll notice the thin red wire with a white tracer coming out of the electronic module on the passenger side which connects to a heavier gauge solid red wire is broken off. There is the equivalent on the drivers side as well (but connected). Not having a wiring diagram, I don't know what it pertains to so I joined them manually which made no difference. What is this wire for?

When I began to remove the former owners stuff he left in the car, I noticed a box of pull out fuses and light bulbs indicating that the former owner had electrical issues with the truck.

Finally, please see the picture of the white relay. The flashers don't work. I think this pertains to them, no? I ohmed out the coil part of it (1 to 3) and get 71.8 ohms. Normal? Available at most part store if bad?
Thanks so much for any help.