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Discussion Starter · #1 ·
The gas gauge in my 1992 jeep Cherokee does not display how much gas is left. When the tank is over 1/2 full, it shows 1/4 of a tank. When it is under, it always shows 1/8 of a tank or empty. Sometimes it is different. I have tested the gauge by jumping the wires that go to the tank with resistors, and that shows that the gauge is fine and the problem lies in the tank. Is this possible to fix without replacing parts? I also can not find just the fuel float system on online parts stores.
 

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One thing you might want to chase down is your ground for the sending unit. If there is too much resistance in it, the gauge will still work but register lower than it really is
 

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No, just unplug it and check from there to ground on the vehicle side
 

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The ground should be attached somewhere near the plug, follow the wire and if it's still attached, remove the ground screw and clean it and the connector.
 

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Discussion Starter · #6 ·
The ground is soldered/welded onto the outside of the sending unit without a screw. When I tested the resistance between the end of the cable and part of the sending unit, there was no resistance. Whats next?
 

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I think you should revisit this. Check the ground to the body. I think you will find resistance there
 

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Discussion Starter · #8 ·
No resistance there either. When the cable is unplugged, there is still no resistance. Isn't there supposed to be no connection when the ground wire is not plugged in?
 

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The rheostat in the tank modulates the full voltage from the gauge. By cutting down on the voltage allowed to go to ground, the gauge will register less than full. Try hooking a wire directly from the ground to a known good ground. The gauge should read full
 

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Discussion Starter · #10 ·
I am confused about what exactly you want me to do. Will the gauge still read full if the tank is actually empty?
 

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Id you ground the wire from the gauge to the sending unit it will read full. This is just a test to see if it is the fault of the gauge or the sending unit or a bad ground being the cause of your problem. I have the same problem on my old Chevy pickup and it is just a bad ground causing it. I have just been too lazy to drop the tank to fix it
 

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Discussion Starter · #12 ·
The gauge reads full if the gauge wire is grounded to the ground wire on the gauge side. So this would mean that the gauge is good.
 

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Discussion Starter · #13 ·
The gauge also reads full if I connect the gauge positive on the gauge side of the harness to the negative on the tank side of the harness. Meaning the tank is also getting ground from somewhere else than the ground wire, and that ground has no resistance.
 

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OK, you are right, the gauge works properly. Now you have to narrow it down to either a ground problem or a sending unit problem. Since your sending unit installs from the front, run a new wire from the sending unit to a good ground and see what happens. Compare with and without the new ground
 

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Then I would guess that yoiu need a new sending unit.
 

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Discussion Starter · #17 ·
One of my family members who is a mechanic suggested that I take the sending unit out, and clean the contacts that the float touches. I am going to try that tomorrow when the rain stops. Is there anything I should know about the process of taking it out that probably isn't covered in a tutorial?
 

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Discussion Starter · #18 ·
Also, If I am not taking the tank off, the fuel doesn't have to be drained right? The fuel level is about 1/4, so it won't be spilling out of the hole.
 

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Right, you will not need to drain it then. Also you should use a new O ring gasket when you put it back together
 

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Discussion Starter · #20 ·
Where would I buy one? (I couldn't find it in the online stores I tried) Is it likely to leak badly if I don't use a new one? If the old one looks fine, can I reuse it?
 
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