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JD 3039R Fuel Sending Unit

5K views 11 replies 3 participants last post by  david.e.sheets.61 
#1 ·
Has anyone experienced problems with fuel sending unit on one of the JD 3000 series tractors? My fuel gauge all of a sudden started pegging out on full, then slowly moves down. I know that it takes a while for the gauge to move once you fill it up, but this is different.

I went ahead and removed rear tire along with the fuel tank and removed the fuel sending unit. Prior to removal, my gauge showed 3/4 of a tank. I drained the tank and got about 1/2 gallon of fuel from the tank. I have to say, the sending unit is an animal I've never seen before! 3 feet long with no float! I have no idea how this thing is suppose to work! I tested the gauge by unplugging the wire from the gauge to the sending unit. I jumped the terminals going to the gauge and was able to watch the gauge go from empty (no jumper) to full (jumping pins). So I'm assuming the gauge is good.

On the sending unit side, I tested ohms on the pins and was getting a high reading. So I decided to take a 2" pvc pipe about 4 feet long. I filled the pipe with water and submerged the "rod" into the pipe. No change in ohm's.

After much frustration, I just put everything back together with the faulty sending unit.

I understand the workings of a standard float, but have no idea how this thing is suppose to work. I REALLY hate to spend $280 on a new sending unit! Especially when the tractor is only about 4 years old!

I've looked all over the internet and can't seem to find anything on this sending unit.

Any advice on testing or using some other type of sending unit?

Any suggesting would be greatly appreciated!
 
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#2 ·
I am not familiar with that sender. does it have a pivot like one with a float has, or is it made to sit stationary in the tank? If it has a pivot, maybe the float has fallen off of the end of the rod?
 
#4 ·
So if it doesn't move and somehow varies its resistance according to how much fuel is in the tank, there are only a couple of ways I can think of that it might work:

1. pressure. The higher the fuel level the more pressure there would be on that piece at the bottom end of the rod, and maybe the resistance varies depending on the pressure? This should work similarly in your test with water in the PVC pipe or diesel fuel in the tank except that water is heavier so the pressure would be higher and the gauge should read higher than the level actually is.

2. Some electro-chemical reaction with the diesel fuel that varies the resistance depending on how much of the rod is contacting the fuel. This might not work at all with your water test, as water and diesel fuel do not share much in the way of chemical composition.
 
#5 ·
I just had another thought. Is it possible that the rod is hollow and the float is inside of it? If so it might be stuck.
 
#6 ·
The rod is not hollow. It actually has a "slice" cut out of it. The shape is similar to a clipper PTO shaft....kind of triangular shaped. A section of one side of the tube is open. Inside the hollow tube is a solid rod. This rod looks like it has small black insulators that keep it from touching the outer tube. Strange contraption.

I did some looking on the web and it almost looks as though its a "guided wave radar". They make them for large holding tanks, but could easily be done with smaller tanks. It actually has "rings" of radar that move around the "pipe". These rings determine liquid levels. You can _tube "guided wave radar" and it explains it better.

I just can't find anything online about this....other than a ton of folks are having issues with them and that JD should issue a recall. I don't know about the pressure sensing or electro-chemical reaction. Sounds to me like they made a high tech gadget when all they needed was a $5 float.

Thanks for replying. I'll keep doing some digging and see if I can't find a better picture of the sending unit.
 
#8 ·
Now you've got my curiosity going. Looks like the outer part is hollow with a solid rod up the middle with a gap between the two all the way around and a slot lengthwise on the outer tube to allow the fuel to get in there. Since diesel fuel itself is an oil and therefore an insulator/dielectric, my guess is that the fuel level in the gap between the inner and outer pieces of metal changes the capacitance between them, and the meter would then somehow reflect that change in capacitance. If my theory is correct, the electrical signal across the wires would have to be AC, not DC. To verify that, set your meter to DC volts and measure across the wires going to the sender when the key is in the run position, and then try with the meter set to AC volts. It could be some high frequency AC, as it would probably be more accurate at frequencies of a few thousand hertz rather han the 60 cycles of regular household AC, so depending on how good your meter is, it may or may not register the AC properly if it is indeed a high frequency.
 
#9 ·
I believe you are correct! I’ve been all over the internet and finally stumbled on something called a Capacitve Fuel Sender. Several manufactures of this type of fuel sender. The only bad thing....putting a typical float in its place won’t work and I have yet to find one 3 feet long! I see a many for boats. Also, I would think you would have to change out the gauge for one to work. It’s a pretty interesting read on how it works. Instead of ohms, it uses voltage (?). They seem to be pretty reliable....from what I’ve read. Even watched a guy build one out of pvc and aluminum slats. He lost me though when he got into the circuitry.

I’ve contacted the tech guy from a company called Centroid. They supply the senders for master craft and other companies. Hopefully he can help me out.
 
#10 ·
Can't you get one from your JD dealer? (Probably expensive but that'll guarantee it's the correct one). No guarantee that any others would have the same capacitance values as the fuel changes level in the tank, and that would throw the reading on the gauge off.
 
#11 ·
It is expensive ($280), and they have plenty in stock....which seemed a bit suspicious to me! Just trying to make a better mouse trap! It's just the fact of it going out after 300 hours on the tractor. If I could find a better way of doing it at a cheaper price, I'd like to go that route.
 
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