Fuel gauge is incorrect – ford truck enthusiasts forums gastritis

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You can ground the wire which plugs into the sender, and turn the key to Accessory or Run, and the gauge should peg Full. You can also insert a resistor between the sender wire and ground, and the gauge will stop short of Full. I forget/never knew the resistor values, but there are three different ones for testing 1/4, 1/2, and 3/4 of a tank. But I think I already know the results – they’ll all give high readings…

So if the gauge is reading higher than it should, then that indicates that there could very well be too much resistance in the circuit. Something like where the gauge retainer nuts contact the Instrument Panel Printed Circuit Board. If one of the nuts is loose or dirty/corroded at its electrical contact point, then that will create more resistance for the circuit. Same goes for the IC PCB. You can give the IC PCB contacts a gentle scuffing with the finest sandpaper you have, or anything 400 grit or higher.

There is another contact point where the gauge cluster harness plugs into the cluster shell. Same thing there regarding dirt and corrosion, and in addition, it’s possible that the IC PCB shifted position slightly, where the connector plugs in, and that could be causing a bad connection.

You can ground the wire which plugs into the sender, and turn the key to Accessory or Run, and the gauge should peg Full. You can also insert a resistor between the sender wire and ground, and the gauge will stop short of Full. I forget/never knew the resistor values, but there are three different ones for testing 1/4, 1/2, and 3/4 of a tank. But I think I already know the results – they’ll all give high readings…

So if the gauge is reading higher than it should, then that indicates that there could very well be too much resistance in the circuit. Something like where the gauge retainer nuts contact the Instrument Panel Printed Circuit Board. If one of the nuts is loose or dirty/corroded at its electrical contact point, then that will create more resistance for the circuit. Same goes for the IC PCB. You can give the IC PCB contacts a gentle scuffing with the finest sandpaper you have, or anything 400 grit or higher.

There is another contact point where the gauge cluster harness plugs into the cluster shell. Same thing there regarding dirt and corrosion, and in addition, it’s possible that the IC PCB shifted position slightly, where the connector plugs in, and that could be causing a bad connection.

I have noticed that it’s usually temperature gauges which are so profoundly affected by extra resistance, but the fuel gauge is basically the same as the Temp (and Oil) gauge, so it should be prone to the same problems.I glanced at it after I noticed the disparity but I didn’t actually unhook the speedometer cable and take it to my bench. I’ll make sure to give it a thorough look. Thank you

So if the gauge is reading higher than it should, then that indicates that there could very well be too much resistance in the circuit. Something like where the gauge retainer nuts contact the Instrument Panel Printed Circuit Board. If one of the nuts is loose or dirty/corroded at its electrical contact point, then that will create more resistance for the circuit. Same goes for the IC PCB. You can give the IC PCB contacts a gentle scuffing with the finest sandpaper you have, or anything 400 grit or higher.

There is another contact point where the gauge cluster harness plugs into the cluster shell. Same thing there regarding dirt and corrosion, and in addition, it’s possible that the IC PCB shifted position slightly, where the connector plugs in, and that could be causing a bad connection.

I have noticed that it’s usually temperature gauges which are so profoundly affected by extra resistance, but the fuel gauge is basically the same as the Temp (and Oil) gauge, so it should be prone to the same problems.I believe the opposite is true, extra resistance will cause a gauge that reads low. To support my theory, look at what happens when you connect the sender wire directly to ground, no resistance. The gauge pegs to the maximum reading.

Notamechanic, You can test the accuracy of your fuel gauge, if you have the cluster removed. Connect jumper wires to the studs on the back of the gauge. Connect the other ends to a 1.5V battery. Wait a minute or two for the needle to rise. If it doesn’t rise, reverse polarity. If accurate, the gauge needle will stop the width of the needle past the first line on the gauge. Add another battery for 3V. The needle should stop a needle width past the 3/4 mark. I just confirmed these readings on 4 spare fuel gauges, all read exactly the same. It is possible to bend the needle to make the gauge read correctly. It is also possible to bend the needle when removing & reinstalling the gauge in the cluster, that may be what happened to yours.