Fuel Gauge Troubleshooting

D&D Farm

D&D Farm

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My fuel guage used to be intermittent. Now it NEVER registers a fuel level. Got around to checking voltages and continuity this morning.

Found the following:

Continuity means, for me, that the ohm meter registers a circuit, NOT a zero reading.

At the fuel tank there are two wires/connections. One is ground, a black, and the other is I assume the hot wire. With the key on or off, neither register voltage; but they both indicate continuity. When connecting the ohm meter across the two terminals I get continuity/a circuit. With the key on, should NOT I be getting voltage to the hot wire? Should I be showing a circuit/continuity on the hot wire with the key on or off? Seems to me that the sensor should not be closed. Does this indicate a short in the sensor?


At the fuel guage there are 4 connections in a pin block at the back of the guage. They all register continuity with the key on or off. One connection, with the key on, registers 12V. Should there be another wire that is HOT with voltage coming in or out of the guage?

Does anyone have a schematic of the fuel circuit. Would like to be able to follow it to the various connections, which I assume are at the fuse block and key, and check the connections..............

Thanks Guys..........Dennis
 
Dennis,

I don't have the schematic, but here is a common setup for fuel gauges.

The 4 wires at the fuel guage:
a) +12v for the guage light when the headlights are turned on
b) ground for the gauge light
c) +12v for the fuel gauge when the key is on
d) wire coming from the sending unit in the fuel tank

The 2 wires on the sending unit: (there is no +12v at fuel tank)
a) connects straight to chassis ground (because it's a plastic tank, metal tanks often only have one sending unit wire)
b) connects to fuel gauge in dashboard.

Testing guage:
With key turned on, ground out the sending unit terminal & the guage should move.

Testing sending unit (may require removal from tank)

a) Connect leads from ohm meter to sending unit terminals.
b) Slowly move arm on sending unit, the reading on the sending unit should change.
You might have to try different ranges on the ohm meter.

Hope this helps, Rich
 
Rich.......Thanks........

To test the guage one grounds out the wire/connector on the tank that is in the middle of the sending unit? The other wire looks like a ground as it connects to the housing of the sending unit. So I watch the guage when I do this with the key on and the guage should do something..........OK......

If I am able to reach inside of the tank over to the sending unit do you think I can perform the other test by doing that or is it sealed some way?

THANKS..............Dennis
 
Dennis,

What I wrote was a generic setup. My RTV900 is up North, so I can't tell you which wires in particular go where.

To verify which wire at the tank is the ground, and which is the sending unit sensor wire, measure both to ground with an ohm meter, then disconnect the sending unit wire from the back of the gauge. The wire that does not read continuity to ground is the sensor wire.

If neither read continuity to ground after removing sensor wire from fuel guage, then you've found the problem..............

You probably could reach in the tank & lift the sending unit float to test. Just be gentle, if anything gets bent, then the unit will be toast.

As far as seals, there is usually a gasket (paper, cork, rubber) between the sending unit and the tank. If you do remove it, don't use gasket sealeing goo when re-installing it. Most gasket seal goo is not fuel resistant & will drip a syrup into your tank (bad days after that!!!!)

Once you identify the wires at the tank, follow the ground wire & verify that it is clean & secure at the ground point, even if it reads OK with meter. If it is hanging on by one strand, or is corroded, the meter will show OK but the function of the circuit will be affected.

Rich
 
Rich and BC..........thanks so much GUYS for your help. The schematic really helped figure it out...........

OK.........The guage was bad; but in trying to figure this out it seems I applied to much voltage to the sending unit in the tank and must have burnt it out.....LOLOLOL....live and learn. Ended up getting the sending unit and the fuel guage this AM.....Really an easy fix once I took out the seat. At the same time I changed out the temp. guage that had been barely registering since new. NOW, I get a valid fuel reading again AND I see that my temp runs 3/4 of the way to hot, the fan kicks in bringing it down to just above 1/2 and cycles......All is good................

NOW to do a 500 hour check starting tomorrow..............ANY advice on bleeding the brakes would be helpful............Does the power steering really need to be changed and does it REALLY hold 8 liters?..............Thanks Guys.......Dennis
 
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