Another Kubota fuel gauge stuck on full

[crazyal]

If Number two is correct and grounding the power wire will indicate a full tank then I would check to see if you have a short. The yellow wire could be chafing on some metal somewhere and when you connect it with the sensor removed you have moved the wire away from the metal. When you reconnect it back up with the sensor in the tank it could be shorting out again. If it works the opposite way and grounding the power wire indicates an empty tank them I would look for a broken wire or a bad connection somewhere. Again, while out of the tractor you could be moving the wires and "fixing" the problem.

With the DVM you could measure the voltage on the power wire both when the sensor is working out of the tank and when it's not working to find any difference. It would also tell you if ground the wire is full or empty.

 

[srs]

If Number two is correct and grounding the power wire will indicate a full tank then I would check to see if you have a short. The yellow wire could be chafing on some metal somewhere and when you connect it with the sensor removed you have moved the wire away from the metal. When you reconnect it back up with the sensor in the tank it could be shorting out again. If it works the opposite way and grounding the power wire indicates an empty tank them I would look for a broken wire or a bad connection somewhere. Again, while out of the tractor you could be moving the wires and "fixing" the problem.

With the DVM you could measure the voltage on the power wire both when the sensor is working out of the tank and when it's not working to find any difference. It would also tell you if ground the wire is full or empty.

Thanks John and Al, today I followed the ground wire all the way down the wiring loom to just where it leaves the cab. The wire looks perfect, no cuts, etc. Tonight I will be going to HF to pick up a cheap ohm-meter. Here is a picture of the top of the sending unit.

 

[pedalstomper78]

WIth this, testing Ohms are the most important things. Remember, the gauge works on the principles of resistance. High resistance = high fuel.

 

[srs]

Here is the latest. First off I want to thank everyone for helping me out with this issue, great group of folks here on TBN!!! Since I know absolutely nothing about using a multi-meter (mm) I went to you-tube and google to try to learn how to properly use one. Here is what I did this morning, hope it makes sense.

1. I was trying to check the ohms. I disconnected both wires from the sending unit. I set the mm to ohms-200. I put the red pointer from the mm to the yellow power wire and the black pointer from the mm to a bare metal spot on the tractor, reading was 40, set the mm to ohms-2000 reading went to 040 so I'm assuming the same reading.

I used the same setting on the mm and put the red pointer from the mm to the ground wire coming from the tractor and I put the black pointer from the mm to a bare metal spot on the tractor and the mm showed a reading of .9.

When I set the mm on ohms-2000 the reading went to 000 then 001. NOT sure if I did this test correctly!!!!!!!!!!!

2. Crazyal recommended I check the voltage. I changed the setting on the mm to DCV-1000. The red pointer from the mm was put on the center post of the sending unit, the black pointer from the mm was put on the ground, reading 000, the sending unit was in the tank. Key was off. When I switched the key to on I got the same reading of 000. The sending unit was in the tank.

I checked the DC voltage with the sending unit out of the tank. I attached the tractor ground wire to the sending unit and the power wire to the center of the sending unit. I turned the key on. The mm was set on DCV-1000. I attached the red pointer from the mm to the center post of the unit (power), I attached the black pointer to the body of the sending unit (ground). I moved the float up and down and the fuel gauge moved accordingly going from empty to full and vice-versa. mm read 000 throughout the movement. NOT sure if I did this test correctly!!!!

3. This test (I think) might indicate the sending unit is good. I took the sending unit out of the tank. I changed the mm to ohms-200. I put the red pointer from the mm to the center post of the sending unit and the black pointer from the mm to the body (ground) of the sending unit. With the float at the lowest setting (empty) the reading was 111, when I manually moved the float higher to the full position the reading went down to 2.5. As I moved the float up and down the reading moved too higher reading toward empty and lower reading toward full.

That's where I am at this point. Any suggestions/comments, etc. are welcomed.
Again I thank you. Stanley

 

[k0ua]

Here is the latest. First off I want to thank everyone for helping me out with this issue, great group of folks here on TBN!!! Since I know absolutely nothing about using a multi-meter (mm) I went to you-tube and google to try to learn how to properly use one. Here is what I did this morning, hope it makes sense.

1. I was trying to check the ohms. I disconnected both wires from the sending unit. I set the mm to ohms-200. I put the red pointer from the mm to the yellow power wire and the black pointer from the mm to a bare metal spot on the tractor, reading was 40, set the mm to ohms-2000 reading went to 040 so I'm assuming the same reading. Yes, it does indicate the same reading on both ranges, but this is a realtivity meaningless test as we dont know what to expect with an ohms check across this circuitry. At least I don't.

I used the same setting on the mm and put the red pointer from the mm to the ground wire coming from the tractor and I put the black pointer from the mm to a bare metal spot on the tractor and the mm showed a reading of .9. OK so you show 9/10ths of an ohm from the black wire, which we assume should go to ground of the tractor and the "bare spot" on the tractor. This could be correct, as we do not know what the test leads would read if shorted together, because you did not tell us. So take your test leads and short them together on your lowest ohms scale (range) and tell us the stabilized reading on the ohmmeter.. I am guessing something like .5 or 5/10 ths of an ohm will be about what you will see. so now subtract this number .5 from your .9 reading and this is the resistance in your black wire, which we assume is going to ground.. so probably about right right for a small gauge wire with some connectors on it. In any case I don't think this is your problem.

When I set the mm on ohms-2000 the reading went to 000 then 001. NOT sure if I did this test correctly!!!!!!!!!!! By going up to the next meter range the accuracy of your test becomes less resolved. In other words The meter cannot resolve the difference in 9/10ths of an ohm and 1 ohm so it does the best it can do and reads out 1 ohm. There is no point in testing what you would expect to be low resistances on a high resistance scale (range) unless you did not read a low resistance on your lower scale.

2. Crazyal recommended I check the voltage. I changed the setting on the mm to DCV-1000. Is this your lowest DC voltage scale?. I would think not. We are looking for a pretty low voltage here, maybe below 1 volt even. So you should have changed ranged on your meter to a more sensititive range. It is ok to start high and work down to lessen the chance of meter damage, but since the highest voltage you are likely to encounter in the tractor is around 14 volts, then there is no point in looking for voltages at the 1000 level.. You meter will not have any resolution at this range.The red pointer from the mm was put on the center post of the sending unit, the black pointer from the mm was put on the ground, reading 000, the sending unit was in the tank. Key was off. When I switched the key to on I got the same reading of 000. The sending unit was in the tank. This test needs to be repeated again with the unit in the tank at a very low DC voltage scale (range) and ideally by moving the float up and down if possible (maybe with a stick thru the filler neck?)

I checked the DC voltage with the sending unit out of the tank. I attached the tractor ground wire to the sending unit and the power wire to the center of the sending unit. I turned the key on. The mm was set on DCV-1000. I attached the red pointer from the mm to the center post of the unit (power), I attached the black pointer to the body of the sending unit (ground). I moved the float up and down and the fuel gauge moved accordingly going from empty to full and vice-versa. mm read 000 throughout the movement. NOT sure if I did this test correctly!!!! Again this test need to be done at a very low voltage range not the 1000 range. as anything below about 1 volt would not be resolved on your meter. and I suspect the applied voltage may be in the millivolt range.

3. This test (I think) might indicate the sending unit is good. I took the sending unit out of the tank. I changed the mm to ohms-200. I put the red pointer from the mm to the center post of the sending unit and the black pointer from the mm to the body (ground) of the sending unit. With the float at the lowest setting (empty) the reading was 111, when I manually moved the float higher to the full position the reading went down to 2.5. As I moved the float up and down the reading moved too higher reading toward empty and lower reading toward full. Yes this is a very good test, and shows the sending unit to be working, however we already knew the sending unit is working because you said early on that when you took the sending unit out and moved it by hand the fuel gauge works normally and tracks the movement of the float.. You see everything works perfectly with the sending unit out of the tank. The sending unit appears good, the wiring and connections and the fuel gauge and all of the associated voltage source circuitry appears to all works as they should.. the question is why does it not work when it is installed in the tank? That is the big question now isn't it? Perhaps the wiring or connections make good connection when you pull it out of the tank, and perhaps the yellow/blue wire is shorting out somehow to ground when you put it back in the tank? Or the float is mechanically not dropping down to the level of the fuel when you reinstall it.. See it has to be a dynamic intermittent problem as everything works correctly when you have the float out of the tank, yet when you re install it.. it does not! Start wiggling and pulling on wires and connections or figure why and if that float is not dropping down to the fuel level.

That's where I am at this point. Any suggestions/comments, etc. are welcomed.
Again I thank you. Stanley

Please see my comments imbedded in your text

James K0UA

 

[srs]

James, thanks! I'll try your suggestions in a little bit.

 

[k0ua]

James, thanks! I'll try your suggestions in a little bit.

Also is there any chance of getting the schematic of the electrical system from anyone so that we might see what this circuit consists of?. We might be able to suggest more tests or interpret the results much more accurately.

James K0UA

 

[crazyal]

Can you post a link to the MM you bought (I'm assuming that you got it from HF). If I can see the front of it I can (as well as others here) can help you understand how to use it. Some mm will automatically scale to the correct level but it sounds like the one you have requires you to pick the scale you need. If so for anything automotive you'll want to use a range that will read 12v (some will have a range of 0-10v while others will have a range of 0-20v) The 10 volt range is too low for most troubleshooting but if you have a 20v range, it will be the one you'll use the most.

To test for voltage you will want to put the red probe on the contact where the yellow wire connects (sounds like you had it in the correct spot). You'll want to sensor out of the tank and the key on. Measure the voltage on the scale that can read 12 volts first and then the next scale down if you don't get any reading with the float in the lowest position (empty tank). Verify that the fuel gauge is reading empty. Repeat the test with the float in the highest position (full tank). Another useful test would be to measure the resistance (ohms) without the wires connected to the sensor while it's out of the tank in both the lowest and highest positions. This will give you the full range of the level sensor.

One final test I would preform while the sensor is out of the tank would be to measure the resistance (ohms) without any wires connected and have someone slowly move the float from full to empty and then back to full. If while doing this test you see the number drop to zero or read "open" (what the meter reads when reading resistance when the probes aren't touching anything) that means you have bad spot in the sensor and it will not read correctly when the fuel is at that level.

With the sensor in the tank and the wires disconnected read the resistance of the sensor. The number you get should fall within the range of what you read when you measured measured the sensor in both the open and closed positions. If it doesn't then you most likely have a bad sensor. Next connect the wires back up and measure the voltage. It should be within the range you measured when the sensor was out of the tank. If not I would suspect that you may have a damaged wire. If so there are a couple of tests to try.

 

[srs]

Can you post a link to the MM you bought (I'm assuming that you got it from HF). If I can see the front of it I can (as well as others here) can help you understand how to use it. Some mm will automatically scale to the correct level but it sounds like the one you have requires you to pick the scale you need. If so for anything automotive you'll want to use a range that will read 12v (some will have a range of 0-10v while others will have a range of 0-20v) The 10 volt range is too low for most troubleshooting but if you have a 20v range, it will be the one you'll use the most.

Can you post a link to the MM you bought (I'm assuming that you got it from HF).

Digital Multimeter - 7 Function, w/ Backlight



To test for voltage you will want to put the red probe on the contact where the yellow wire connects (sounds like you had it in the correct spot). You'll want to sensor out of the tank and the key on. Measure the voltage on the scale that can read 12 volts first and then the next scale down if you don't get any reading with the float in the lowest position (empty tank). Verify that the fuel gauge is reading empty. Repeat the test with the float in the highest position (full tank). Another useful test would be to measure the resistance (ohms) without the wires connected to the sensor while it's out of the tank in both the lowest and highest positions. This will give you the full range of the level sensor.

A) I set the mm on DCV-20, the sending unit was out of the tank, gauge works correctly, reading was 000. I also set the mm on DCV-2000m and it read 190 with the float at full level, about 1600 1/2 full, and 1 on empty.

One final test I would preform while the sensor is out of the tank would be to measure the resistance (ohms) without any wires connected and have someone slowly move the float from full to empty and then back to full. If while doing this test you see the number drop to zero or read "open" (what the meter reads when reading resistance when the probes aren't touching anything) that means you have bad spot in the sensor and it will not read correctly when the fuel is at that level.

B) I removed the sending unit from the tractor, no wires connected. mm set on ohms-200. empty the reading was 113, 1/2 full the reading was 27, and full it read 4. To get these readings I slowly moved the float up to full then down to empty.

With the sensor in the tank and the wires disconnected read the resistance of the sensor. The number you get should fall within the range of what you read when you measured measured the sensor in both the open and closed positions. If it doesn't then you most likely have a bad sensor. Next connect the wires back up and measure the voltage. It should be within the range you measured when the sensor was out of the tank. If not I would suspect that you may have a damaged wire. If so there are a couple of tests to try.

C) I was a little confused with the above paragraph so here is what I did. I set the mm to ohms-200 and got a reading of 6.0. I also set the mm to ohms-2000 and got a reading of 007.

I also traced every stinky wire to the gauge clusters, pulling, pinching, twisting, etc. to see if things would change, needless to say it did not.

Also is there any chance of getting the schematic of the electrical system from anyone so that we might see what this circuit consists of?. We might be able to suggest more tests or interpret the results much more accurately.

James K0UA

James, I do not have any connection with anyone other then members here regarding a schematic drawing.

 

[k0ua]

Well we are running out of ideas here, why in heck when you put the unit back in the tank, it no longer works,.. look at how it is made, and let us look at it. take some photo's of it.. dont put the screws back in.. just dump it in the tank and take it out.. and now tell me what in heck is the difference? It is almost like the yellow wire connection is grounded and no longer going thru the potentiometer of the sending unit... look it over carefully while thinking of that. I am starting to get frustrated, and goodness knows you must be exasperated with this thing.. I will give you this.. you sure have stuck with it, and tore the heck out of things and dug into this problem.

James K0UA