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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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