4310 fuel sending unit

[zaw]

I just replaced the fuel sending unit on my JD4310. The gauge goes to full when the key is turned on but it does not read correctly it stays just below full even when I manually move the float. Anyone have any ideas or similar problem. Zak

[JD5210]

What was the fuel gauge doing before you replaced the fuel sender? If it was doing just what it is doing now, I would check the positive wire to the gauge and see, if it is grounding against the frame some place.

At the sender with the wires disconnected the gauge should read empty. Touching the two wires at the sender together the fuel gauge should go to full.

[zaw]

When I attach wires to unit it reads just below full when I touchthe wires together it reads above full. So far the wire looks ok and is inside protective flex tubing.

[JD5210]

What was occurring that made you decide to replace the fuel sender? With the tractor off, key in the run position and wires disconnected at the sender what does the fuel gauge show?

While most likely the new fuel sender is working correctly you could test it using an ohm meter. Most likely the range will be different, but on my 5210 the range is between 4.5 97.5 ohms.

[mfreund]

My 4310 does the same thing. I put 5 gallons in when the gauge does not move anymore. Design defect in my opinion.

[zaw]

it always read close to 3/4 full with old unit. with the new unit it reads just below full. when i leave the key on and disconnect the unit the gauge goes to empty. i noticed yesterday when i connect the unit and turn the key on the gauge reads just below full, and when i tap on the dash the gauge moves slightly towards full. i have done that several times.

[JD5210]

If you are open to trying a few other things. Using the old fuel sender and an ohm meter see what the readings are when at the empty, half full and full. Using the old fuel sender and leaving OUT of the tractor, but connect to the fuel gauge move the float up and down and see what happens. What I am wondering is there something in the tank that is keeping the float from going down.

Does anyone have a tech. manual for the 4310 and could you share what the ohm readings high and low for the fuel sender are?

For what it is worth here is how it works.

Sender assembly consists of a movable float mounted to a variable resistor (potentiometer). Resistance of potentiometer on gauge sensing circuit controls the fuel level shown on gauge. As float moves up or down with changes in fuel level, electrical resistance of potentiometer changes accordingly. When tank is full, resistance is low and gauge needle moves to full position. When tank is empty, resistance is high, and gauge needle moves to empty position. Potentiometer resistance between these two positions varies in direct proportion to changes in fuel level. This allows gauge to accurately display quantity of fuel in tank regardless of its level.

[fxrupr]

From my experience the sending unit and gauge have to be matched in resistance range and polarity. The gauge of wire you use from the tank to the gauge in the dash is critical as well because the wire has its own resistance as well. I have resurrected several old sending units which had a corroded or broken connection on one end or the other of the potentiometer which is the bunch of tiny wires that the float contact rubs against as it moves up and down. You can do a dry run if you hook your battery charger set to 2 amps to the gauge and ground the sending unit. By moving the arm back and forth you can watch the gauge move. It responds slowly. A good wiring schematic of your machine should show the gauge of wire to use and length. If you look your machine up on a NAPA site it may tell you which gauge crosses to yours and what the resistance is supposed to be. There are only so many different different ranges and yours will be one type or another. Check and see if the part number and / or resistance are correct for your application.