E350 gas gauge intermittant
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E350 gas gauge intermittant
I have a 1989 E350 Fleetwood motorhome. My problem is that the gas gauge shows empty most of the time. While driving I have noticed the gauge working properly and it will continue to work until I turn the ignition off. Then it will be back on empty and shows no movement when I turn the key on. I bought it from the original owner and she said it has done this for the past few years. Is there a current source IC supplying the power to the sending unit or just the 12v from the fuse block? I can't get to the fuel tank wires without dropping the tank. Any help would be appreciated.
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Joined: Jan 2001
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From: Virginia
12v feeds the instrument cluster. I am not sure about your year vehicle, but the older ones had a instrument voltage regulator mounted on the cluster. The voltage leaving this unit fed all the guages in the cluster. I believe the later units did not have a regulator, but I don't know the transition year.
So one side of all the guages are fed voltage anytime the key is in run. The other side of the guages is not grounded. Instead it is run through a wire to the sending unit, which is a variable resistor. The other side of the sending unit is grounded. So the sending unit varies the ground of the guage, which makes the needle read higher or lower.
To test the wiring and the guage, all you have to do is find the wire going to the sending unit, and with the key on, let it hang in the air(very high resistance) and then ground the wire(very low resistance). This will make the guage swing full scale back and forth if everything is working correctly.
So one side of all the guages are fed voltage anytime the key is in run. The other side of the guages is not grounded. Instead it is run through a wire to the sending unit, which is a variable resistor. The other side of the sending unit is grounded. So the sending unit varies the ground of the guage, which makes the needle read higher or lower.
To test the wiring and the guage, all you have to do is find the wire going to the sending unit, and with the key on, let it hang in the air(very high resistance) and then ground the wire(very low resistance). This will make the guage swing full scale back and forth if everything is working correctly.
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Joined: Sep 2003
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From: Northern Indiana
This has happened on a chitload of Fords dating way back and it's very, very common. I've talked to a lot of RV owners of E-350's that have guage problem. I'm included in that. Almost always (99%) it's the sending unit. If it had anything to do with the instrument cluster you'd see other problems on the cluster.
You can find the feedwire behind the instrument cluster in one of the plugs (don't remember which at this time) and read the tank sensor resistance. I believe it goes from 70Ω down to 0Ω. I'ts inversely proportional so 70Ω is empty and 0Ω is full.
The sending unit is not cheap as you have to buy the whole drop in package. I just keep track of my miles.
You can find the feedwire behind the instrument cluster in one of the plugs (don't remember which at this time) and read the tank sensor resistance. I believe it goes from 70Ω down to 0Ω. I'ts inversely proportional so 70Ω is empty and 0Ω is full.
The sending unit is not cheap as you have to buy the whole drop in package. I just keep track of my miles.
