Fuel gauge problem

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Jul 17, 2012 | 10:11 AM

tww4929

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Fuel gauge problem

My 2002 F-250 has developed a fuel gauge problem. It reads EMPTY. A mechanic friend said I would have to pull the tank. Is this true? Any suggestions?

Jul 17, 2012 | 10:29 AM

srteach

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The fuel gauge system is a linear resistance circuit. If it is infinite resistance or no resistance, you are at the extreme ends of the reading.

IIRC, if the gauge reads empty, it means there is infinite resistance (open circuit). No resistance is not good either if the tank isn't completely full or completely empty. Check the fuse first. If a fuse is blown, you have a short in the wires. Check the wiring and plugs before dropping the tank, one may have come loose or been broken. It is literally a 2 wire circuit.

then you can:

test voltage at the tank plug to the dash side (place leads on both connections going to the truck). With key in run position, there should be DC voltage there.
Check both of the same wires as follows. One should have voltage, the other should have continuity.
Test resistance (ohms) from the other side of the same plug to the sending unit.

This will tell you if there is a broken wire to the dash or actual infinite / no resistance in the sending unit. If there is infinite resistance (or none), you will have to drop the tank or get to the sending unit somehow. It is possible you have a bad float.

Jul 17, 2012 | 10:41 AM

tww4929

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Thanks, srteach

I only have about 50 miles on this tank, so it is not empty. The gauge will go to full when I first start it, but then falls to empty a short time later. Do you know if this is a common problem? Do you know where the wiring might be? Is the fuse in the common panel or the one under the hood? Thanks for your help.

Jul 17, 2012 | 06:18 PM

srteach

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Quote:

Originally Posted by tww4929

I only have about 50 miles on this tank, so it is not empty. The gauge will go to full when I first start it, but then falls to empty a short time later.

Does it do this every time, and does it fall after specific length of time after starting? Even if it isn't wiring, better to check wiring before dropping tank.

Quote:

Do you know if this is a common problem?

No idea if it is a common problem.

Quote:

Do you know where the wiring might be? Is the fuse in the common panel or the one under the hood?

The wiring plug I talk about is probably close to or on top of the tank. There are two wires that go into the fuel pickup assembly. I don't know which fuse it is, but it should be in the list in the owners manual.

Do yourself a favor and empty the tank before trying to drop it (if you do drop the tank). You probably have close to 250lbs of fuel in the tank.