Help troubleshooting fuel gauge

[Telkwa]

I hope nobody minds if I sorta re-post this. I added the info to an older thread but wondering if it didn't get noticed that way.

L3301 tractor. Only a year old, but stored under a lean-to where rodents got to a few wires last winter.

The fuel gauge does not read fuel level. It jumps to 100% momentarily when starting the tractor, like the other gauges, so the gauge itself isn't completely dead.

There's a tiny bit of rodent damage about a quarter inch behind the plug that connects to the tang on the fuel sensor. I checked for continuity from the plug to the Y/G wire at the back plug of the instrument panel. The wire's still good.

I turned the tractor keyswitch to "on" and tapped the fuel sensor signal wire to the fuel sensor ground wire, expecting to see the gauge jump, but it didn't move.

The fuel sensor is out of the fuel tank. It's rusty as heck and doesn't seem to respond to movement of the float at all. I get a couple of ohms at all positions.

Does anybody have some advice? The fuel sensor seems to be kaput, but I should be able to fake a signal to the gauge and see it move. I don't know how to do that.

 

[Daren Todd]

Shorting between the ground post and signal post on the gauge itself will verify the gauge. Gauge should peg out.

Next, short the end of the signal wire to a good clean ground on the frame. If gauge pegs out. Then wire is good. If it doesn't move the gauge, then there is a break in the wire somewhere.

If both of those tests check out good. Then chances are good the issue is with the sending unit. Electrical contact cleaner can be used to clean the contact strip on the sending unit if it has one.

 

[scdeerslayer]

Just because you can read continuity through a wire that doesn't mean that wire can carry the required current. I've learned this plenty of times diagnosing issues with boat wiring. You wouldn't think a fuel gauge would need that much but if there's only a minuscule amount of connection at the damaged area that could be your problem. You should cut the damaged piece of the wire out. That close to the end of the wire you'll probably need a new plug and possibly a short piece of wire.

 

[Telkwa]

Hey, guys, thanks for the help. scdeerslayer, I know what you mean about a wire that's half its original size causing trouble.

Just wanted to make a report.

So yesterday morning I'd rechecked everything electrical that I could think of, and wrapped multiple layers of electrical tape around all the wiring near the fuel sensor. It was Sunday, so not much I could do about buying stuff. Monday morning I was gonna buy a fuel sensor (mine wouldn't show resistance) and ask if there was a test for the gauge itself in the instrument cluster.

My wife walked by and asked me to show her the problem. I'd reinstalled the fuel sensor back into the tank. So all I had to do was plug in the instrument cluster and turn the key.

The fuel gauge responded. What??? Yeah, it came off zero. A little reluctantly at first, then it slowly climbed to about third-full. I poured a few gallons into the tank, turned the key to "on" and the gauge responded to the new fuel level. Turned it off, filled the tank to the brim, turned it back on, and the gauge jumped to full.

My wife is now saying "we" fixed it.

This might be one of those times where it's best if I don't ask too many questions. The fuel level sensor was showing a few ohms regardless of float position, so it appeared to be broken. And the gauge wouldn't respond to grounding out the signal wire with the key "on". So it sure looked like one or both parts had failed.

I went back to the tractor several times that afternoon, and the fuel gauge lit up every time. Weird.

One possibility might be that the ground wire was also damaged by rodents, and the cut wires got shoved back together during re-taping. But the mice had only attacked in a couple of spots. It's pretty easy to tell where that corrugated outer wire sheath is still intact. So I don't think the ground wire was damaged.

Judging by the rusty condition of my fuel sensor (the tractor's only 2.5 years old), I'm guessing it'd be a good idea to keep the fuel tank full, especially if it's setting for months during the winter.

 

[D2Cat]

May have been some oxidation on the resistor the float arm moves on. Your activity with it may have been enough to make contact again.