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EricF

520H Fuel Gauge & Sender Issue

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Hoping to get some ideas and opinions here. The fuel gauge on my 520H drops to empty when the ignition is off, but when given power, it always deflects to "full". I checked the voltages on the gauge terminal according to Toro's Demystification Guide, and it appears OK according to the test voltage chart. I took the fuel sender out, cleaned the terminals, inspected it, and checked its resistance according to the Demystification guide. The sender reads out OK on my meter -- the resistance values are correct and change smoothly until the last little bit of the float's travel near empty when the resistance suddenly goes way up beyond spec, but I doubt that's a problem as it should just make the gauge read absolutely empty if the fuel ever goes that low.

 

Here's the problem -- the fuel gauge reads full or nearly full no matter what position the float is in. If I move the float from "full" to "empty", the gauge will drop just a tiny bit, from just past the "full" mark to just below it. Wiggling the float will wiggle the fuel gauge, but just a tiny bit -- it always reads near full even though it will move slightly.

 

Looking at the wiring diagram, I can see that the float is just inserted between ground and the "S" terminal on the gauge. Is this more likely to be a ground problem or a gauge that's bad? So far, I haven't found where the ground connection on the sender end is located. Both wires to the sender look like they're disappearing into the same bundle going back toward the front of the tractor. On the other hand, if the sender's ground is tied to a bolt somewhere in the rear end of the frame, I haven't found it yet to check it. (But that doesn't surprise me; when I took off the fenders I found gobs of mud mixed with spilled oil packed everywhere that I had to clean out, so it might still be hiding under a blob of grease that I missed.)

 

Kind of puzzling -- has anybody here had a similar kind of fuel gauge / sender problem?

 

Edit-- A thought just occurred to me... Does the sender circuit run through the dreaded 9-pin connector, and could that be a possible source of the problem? I haven't dared to disturb that connector yet...

Edited by EricF

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Following with interest here Eric, mine does the same thing except that it is erratic. Some days it will work fine and others it does what you described. I have a NOS sending unit on the shelf but have not gotten around to deal with yet. Mine is such a gas guzzler I just got into the habit of gassing up every time I turn the key! :)

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Some fuel gauges when they lose the sensor input will read full.

 

Make sure the wires are connected properly to both the gauge and sender unit.

 

Sender or gauge may be faulty.

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47 minutes ago, cleat said:

Some fuel gauges when they lose the sensor input will read full.

Good to know that's been seen before as a possibility. I haven't ruled out a bad ground or grounded-out positive wire in the sender circuit... I still haven't traced every inch of the sender line in the wiring harness. Not exactly looking forward to that... Getting underneath the rear fenders turned into an exercise in freeing, and in a couple of cases cutting and extracting frozen, rusted bolts and re-tapping threads in the front fender bracket. Hopefully, the worst is over. :wacko:  On the other hand, everything is back together now with anti-seize on the threads and ready to work again. Just need to trace more wires.

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Hello, I now have a 520H with everything fixed on it except the fuel gauge which seems to have the same problem you all have or have had.   I see the problems but so far no one has posted a fix.  I have checked the sending unit and it appears ok.  I looked at the wiring diagram and it does no match the way the gauged is wired.  It is a real pain to get the fuel gauge out to replace it (which I have another one) so I was hoping someone would post what they found.

 

Thanks Bob

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When you unplug the sender with the key on does the gauge show empty ?

 

If so, quickly touching the two wires together that go to the sender should make the gauge show full.

 

If this is true then the sender is bad or at least needs the connectors cleaned.

 

If not, please let us know what happens and we will go from there.

 

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Yes the gauge went to empty.  I think you are removing the ground according to the print. The other wire goes right to ground. So touching them together reconnects the ground and it goes to full.  I did  take the sender out and measure the resistance and got 30 Ohms full and about 230 ohms empty.   Interesting thing I hooked my replacement gauge across 6v and it went to full I would have thought it would go less than full.

Thanks 

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Fuel gauge issue resolved.  After doing all the checks recommended buy you all  I changed the fuel gauge and all works fine.  That fuel gauge is nothing more than a small amp meter and the sending unit varies the electrical current passing through it.  I would bet that most of the time the fuel gauge fails causing it to read full all of the time.   Again thanks for all the suggestions.

 

Have a great day 

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