Monaco Fuel Sensor

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weewun

Well-known member
Joined
May 17, 2013
Posts
380
Location
Henrico, North Carolina
Fuel Gauge stopped working correctly on trip to FL this year.  When full it reads 1/4 tank and decreases from there.

Removed and cleaned all four connections to the Fuel Sensor, checked voltages and Gnd connection -- all good.  The Gauge will do full scale deflection with application of voltage.  Removed Fuel Sensor and measured resistance as follows:

1.  Gnd to 12vdc terminal 280Kohms'

2. Gnd to Fuel Gauge take-off 129ohms

3. 12vdc to Fuel Gauge take-off 279Kohms +

Don't know what they are supposed to read.

Was expecting some kind of float arrangement but it must use the height of fuel in the column to control resistance.  Am going to try to locate a new Fuel Sensor, will appreciate all your insights and input.
 
You say you checked the ground, at the sender or at the gauge? My dash was full of poor grounds. If I was betting, I'd bet that you'll need to correct the ground behind the dash and that'll fix it. Just a jumper wire from a known good ground to the gauge will give you a quick idea if that's the problem.

Ken
 
I checked the wiring and was able to get good deflection (full scale) on the gauge.

Come to find out the Fuel Sensor is a capacitance variety so my ohm readings are essentially useless, the height of the Diesel fuel in the sensor varies the dielectric of the capacitor (inner and out tube of the Sensor are the capacitor plates) and the electronics in the head of the Sensor convert that to a DC voltage to feed to the Gauge.

I have a new Sensor on the way and will compare Ohm readings just for information before I install,

Shall update after I install the new Sensor.
 
Installed the new Fuel Sensor and the gauge is reading properly.  I had some concerns as I like to be able to definitively prove the item is bad before spending $180 as it is I convinced my self that it was the remaining possibility after verifying the voltages, continuity and connection integrities.  Big sigh of relief.

I did notice that the encapsulated top of the old sensor had raised a little and I surmise that moisture got into the electronics on the sensor.
 
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