1988 V6 4runner here. I'm having some kind of electrical issue on what I think is the negative side of my fuel pump. The truck will crank and if I hook up a wire from the negative side of the battery terminal to the negative side of the fuel pump, the pump will spin and the truck will run.

If I run a wire from the negative side of the fuel pump to ground, the truck will not run.

One of the coolant lines broke and the truck overheated about a year ago. After that it would not run. I think the overheating and steam in the engine compartment may have damaged one of the wires which caused the fuel wiring issue. I have absolutely no idea how to find this fault.

Other than running a line directly from the neg battery terminal to the neg fuel pump terminal, how do I solve this issue? Would there be any issues with hardwiring the fuel pump to the battery???

Thanks everybody

 

If your fuel pump works off the negative side of the battery yet fails to work you have a poor ground where your trying to make one.

figure out just where the white/ black wire is open because it might be enough to cause the positive side to open or short

Have you jumped B+ to FP in the check connector that bypasses the EFI Relay and The Circuit Opening relay just to be sure.

if your sure it is only the ground circuit which is the white/black wire off the fuel pump harness that grounds on the right fender check the right fender ground for being corroded

any other electrical circuits not working ?? Seems strange the only one circuit would be open.

A nice new hole with a clean bolt might give you a good ground might need to add a battery to frame ground

I added a battery to frame ground to make wiring trailer brakes and lights easier.

Good Luck

 

Dude that's exactly what it was, I went back and looked at the neg line off the fuel pump and the wire had broken yet it was still connected by the plastic casing. This baby runs again!!!

 

On my '94, the bed is not grounded. (It sits on vibration isolators which insulate it from the frame.) So the taillights have a separate wire back to the harness for ground.

If your fuel pump is the only victim, rather than trying to change the ground-state of the entire frame (or body), I'd run a wire just to bring ground back to the pump.

 

[QUOTE=scope103;52466296]On my '94, the bed is not grounded. (It sits on vibration isolators which insulate it from the frame.) So the taillights have a separate wire back to the harness for ground.

If your fuel pump is the only victim, rather than trying to change the ground-state of the entire frame (or body), I'd run a wire just to bring ground back to the pump.[/QUOT

This set up was installed be you and the hardware is all non conductive I have never seen that . Interesting

 

YES! There would be a problem. A BIG problem.

Toyota likes to switch ground in and out to turn a circuit on and off. For example, the COR applies ground to the fuel pump to turn it on. If you apply a direct connection to ground, the tuel pump will come on as soon s the key does. If you get into an accident, it won't shut down. The system will remain pressurized, and a crack or break somewhere and you'll have fuel being pumped out onto the ground. Talk about DANGEROUS!

You need to check out the COR, and MAF. The COR, when the key is first turned to STArt, thus closing the COR first half, applies ground to the fuel pump, and once some air begins to flow through the MAF, a switch in it closes, and it applies a ground to the COR, holding it's other half connected, and through the COR, ground to activate the fuel pump. If there's a crash, the air stops flowing through the MAF, removing the ground, deactivating the COR, and through it, the fuel pump. No pressure, no flowing out of broken systems, no danger. Or at least much less.
The COR is easy to test, and the MAF's switch is even easier. It's either open, or closed. Two contacts on the left and of the MAF's plug. Take the plug off, and ohm between them. If it's open (infinity ohms), open the vane, even a little. The switch should go closed (zero ohms). If it checks out, the COR is bad. $65.00 from the dealer. Small price for the safety it gives you!

You may also need to check the wiring between the COR and the key switch, and between the MAF and the COR. Again, if you need a schematic, let me know.

If you wish, I can show you the schematic of the circuit the fuel pump uses, and include the MAF and COR.
Hope this is a little help...
Pat☺

 

I'm 99.99% sure that is not correct.

While lots of things on your Toyota are switched-ground (for instance, the FC pin of the VAF), the fuel pump is switched-battery. If geoduke has an open in the W-B from the fuel pump back to BG1, running ground from the battery to pin 2 of the Fuel pump should be just fine.

(Of course, all this depends on geoduke having something similar to factory wiring, and having described the problem more-or-less accurately.)

 

Seems you missed that the problem was a broken wire at the fuel pump connector with the insulation intact .

The OP found the issue and repaired it Now good to Go!

 

Another note on this, the ground wire ends up as a single pin in the connector under the seat for the tail lights, fuel pump, tank level sensor, etc. If the fuel pump ground is bad, but the tail lights work (and gas gauge), then it's between the connector on the cab to the fuel pump itself. If the ground supply is bad, tail lights won't work as well, and the issue is farther down the circuit (body ground locations, bad wire, etc).

Anyway, glad OP found the issue, wires breaking right at the connector are always fun to find. Did you replace the terminal in the connector, or install a pig tail, or did you splice the two wires together to bypass the connection? I've made the complete tail light harness in the past, so I have all of the connectors, so could make a pig tail if it wasn't fixed correctly (could just make a pig tail for the single terminal too).