Fuel gauge /sending unit '94

[cooksmtn]

My fuel gauge occasionally would read empty. When operating, it read accurately. Now it always reads empty, which I believe indicates an open circuit, making me think I have a bad ground. I know it could also be a connection above the tank. Before I start crawling around under the (muddy) rig, I thought I'd explore other possibilities, but I don't have a wiring diagram.

What should I check before mud crawling of the worst kind?

 

[FR-425]

There is also a resistor circuit board on the back of the gauge, which slows down the needle from bouncing wildly when the gas is sloshing around in the tank. these can fail leaving an open circuit.

 

[roscoe 0202]

if the resistor goes bad usually all gauges except bat guage will go to full hot full tank max oil pressure. go under ground the guage wire guage should read full if it is the sender.
roscoe

 

[cooksmtn]

Thanks for these suggestions. I think my first stab will be to check the connector above the tank, as I may be able to access it from the wheel well if I remove the wheel. Opening that connector should allow me to check resistance of the sender, and to short/open the gauge wires to check gauge function without opening the dash.

 

[Roadrunner777]

94exp_fuel_gauge_sch

• Roadrunner777
• June 27, 2014

94exp_62-3

• Roadrunner777
• June 27, 2014

 

[cooksmtn]

Thanks much, Roadrunner.
This is exactly what I wanted

 

[FR-425]

All things considered it is most likely the sending unit in the tank.

 

[Centaurious]

The water in our fuel (from the ethanol) does bad things to the electrical connections and resistor sweeps for the fuel sending unit. I've seen a fuel pump assy from a daily driven car that looked like it was fished out of the ocean. The car quit because the clamp holding the fuel line on the pump failed and the line blew off.

 

[cooksmtn]

We have the 10% ethanol here, and from what I've seen on these boards, I figure I'll just bite the bullet and drop the tank, and replace both the fuel pump and sending unit. I just did a pressure test (OK), since the wife ran the rig out of fuel recently. I'm just waiting for the roads to dry up (we live 5 miles off the pavement), and the bottom of the rig is nasty with mud. I'll post my results when it happens, to maybe help others out.

 

[Roadrunner777]

When you start working on this, you will probably find the wiring harness going to the pump/sensor, and there is a connector there, so if you wanted to verify it is the sensor before dropping the tank, you could probably do that. Also, a fair number of people, myself included, have cut an access hatch under the left rear seat, rather than drop the tank. There are threads on this, and I'm not specifically saying you should do it... it's a delicate job cutting sheet metal blind with fuel lines right there. Then, you know.... sparks, fuel, fire, all of that. But, if you do it, then changing the pump in the future is a pretty quick job.

Thanks in advance for posting back your results!

 

[damnford]

them sending units are not cheap.

 

[cooksmtn]

them sending units are not cheap.

Just an update:
All wiring checked out OK, so I dropped the tank, replaced sending unit and pump. Nothing obvious wrong with old sending unit, but everything now works as it should.