'06 Montana 4340 - Gas Gauge Issues; Key On Shows Constant Full

[cpntexas]

'06 Montana 4340 having gas gauge issues - KEY ON Shows Constant Full

Took out the Sender/float and measured a full swing from UP [full] position 10 ohms to 127 ohms full down [empty]

Key OFF
Tank 1/3rd full 5 of 16 gallons [spec]
Gauge sits at E [expected]
Sender disconnected - 2 wire reads 43 ohms so seems representative of 43 / 127 = 33%

Key ON
Sender connected sits at F - ??? Does this indicate a short at the gauge wiring since it doesn't see the variable resistance caused by float moving??
Tried to simulate fuel level by putting a 30 ohm resistor across the gauge side wires with sender disconnected, still read full.
Sender disconnected sits at E [ normal expected infinite resistance seen by gauge ]
12vdc does exist on the 2 sender wires

Is the gauge bad or a short from the gauge to Sender connection?

How can you trace this issue to the source as it seems the instrument cluster is integrated into a circuit board and a common wire bundle goes into the dash rear?

 

[Roadworthy]

Remove the wires from the sender. With the key on measure the voltage. I don't know how much voltage is supplied to the sender. Check the schematic to see what voltage should be applied to the sender / gauge. Perhaps it should be twelve volts, perhaps not. Some instruments use a five volt supply. Usually that regulator goes open. Sometimes it shorts allowing full voltage to your instruments. If you have a temperature gauge it's usually on the same regulator if there is one.

 

[cpntexas]

Roadworthy,

12 volts under the conditions you specify.
I do not have a schematic to determine so working from logic unfortunately.

Temp gauge also acting the same..... Any idea where to physically locate that regulator you mention ?
This sounds like a good trail to follow as the gauge acts like it sees a short on it's side of the sender connector with key on as zero resistance is close enough to the full sender swing of 10 ohms.

 

[Tinhack]

It could be on the back of the gauge cluster as a separate unit (mine is) or it may be part of the cluster's printed circuit board--If it has one.

 

[ROUSTABOUT]

I doubt I've had a working fuel gauge on a tractor since Jimmy Carter was president. Never ran out of fuel either.

 

[cpntexas]

I doubt I've had a working fuel gauge on a tractor since Jimmy Carter was president. Never ran out of fuel either.

I hear ya, it's not so much the fuel gauge as I can ohm the sender leads and know the level, but it also affects the temp gauge and Id like to know of any issue as the prior owner got a hot issue and did not know till much later w/ steam, boil over and all.

This tractor has to last!