L3940 Fuel Sensor

[Ridger]

I have a 2007 L3940 HST. The fuel gauge hasn't registered correctly for quite some time. It only registers at 1/4 full regardless of the fuel level. Recently, I had to replace the battery so I decided to also pull the fuel sensor and check it. It was a little corroded but the float and wiring were intact and the float still moved up and down. I cleaned it up and checked the ohms and it read within the recommended WSM ohm specs when in the full level and empty level. I then connected the fuel sensor to the sensor wiring harness and connected a ground wire from the body of the sensor to the tractor and moved the float arm up and down. The fuel gauge went to empty when the float arm was down and triggered the low fuel alarm. However, when I moved the float arm up the fuel gauge would only go to a little over half full. The fuel gauge never registered full when the float arm was fully up.

Is it possible the fuel sensor is faulty even though the ohm readings checked out fine? Thanks for your time.

 

[PoTreeBoy]

I have a 2007 L3940 HST. The fuel gauge hasn't registered correctly for quite some time. It only registers at 1/4 full regardless of the fuel level. Recently, I had to replace the battery so I decided to also pull the fuel sensor and check it. It was a little corroded but the float and wiring were intact and the float still moved up and down. I cleaned it up and checked the ohms and it read within the recommended WSM ohm specs when in the full level and empty level. I then connected the fuel sensor to the sensor wiring harness and connected a ground wire from the body of the sensor to the tractor and moved the float arm up and down. The fuel gauge went to empty when the float arm was down and triggered the low fuel alarm. However, when I moved the float arm up the fuel gauge would only go to a little over half full. The fuel gauge never registered full when the float arm was fully up.

Is it possible the fuel sensor is faulty even though the ohm readings checked out fine? Thanks for your time.

Ground the terminal coming from the gauge at the sender. The needle should read 'full'. If it doesn't, you most likely have a bad connection going to or from the gage. If it does read 'full', since you've checked the sender, you must have a bad ground connection around the sender.

The power to these gauges goes from the main switch to the gauge, then to ground through the sender which varies the current via a variable resistance. The ones I've seen actually have a heater element wrapped around a bi-metallic strip, so there is noticeable current required to make the needle go fullscale.

 

[lugbolt]

fuel level sensors were a sore subject with me when I was working at the dealer. They'd ship the tractors on a boat, around saltwater (obviously), then they'd sit at port for a while, then on a truck to a distribution hub, then from the hub to a dealer. Then sit in a crate, outside, at the dealer for who knows how long. In this area, 3-6 months depending on how many they ordered and how sales were. Then they'd get assembled, maybe they'd sit on the lot another month or three. Put a tank of fuel in it, gauge reads empty or 1/4 or whatever and doesn't move, so then I'd pull the sensor out to find a bunch of rust on it. Lots of them! Some were a bear to replace, but it was my job and I did it. I certainly don't miss it though. Not for what little bit it paid given the amount of physical work it took, of which my body pays the price for every single day of my life.

 

[Ridger]

Thanks PoTreeBoy for the help. I checked the gauged and it was fine so I checked the ground at the sensor. That's what turned out to be the problem. I made a jumper wire and grounded the sensor to the frame and now the fuel gauge seems to be working properly.

Thanks again for the help!