1981 chevy c20 gas gauge

can any of you please tell me if there is a way to get my gas gauge to read right as when it's full it reads 1/2 a tank now. I just bought the truck so
I have no idea how long this has been going on. Thanks for any help you may have,,,,,
--
Chuck Hembree
Hi-Tec Tool, Inc
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Does it stay at the 1/2 tank mark until you get down that low?
Sounds like the sending unit is bad in the tank.
~jp
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Chuck H. wrote:

    Get a factory wiring diagram for the fuel sending unit. Drop the tank and test the sending unit is reading properly. Then test the wires, then test the gauge. Charles
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I hate to tell you this but most gas gauges in the older trucks rarely read accurately. But if you want to take a stab at it you should drain the tank, replace the intank sender then re-add enough fuel to give you something close to a half tank and see what it reads. If it is still off then replace the gauge module. I just replaced my fuel tank and sender in my suburban and my gauge is still off... Just seems to be a quirk with these trucks. Just pay attention to your mileage. Sender can be had from any autoparts store and the module can be had from LMCtruck. Don't know of anybody else that will have it.
Good luck, mark
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Just curious... is this inaccuracy caused by the sender or gauge or both?
Reason I ask is...I plan to swap everything over to Autometer gauges in the future, including the fuel gauge. Will the aftermarket fuel gauge be as inaccurate as the factory one?
~jp
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not sure,,,,lol,,,,I'm an old hot rodder from the 70's, and I've never had this problem before as I never had any gas to speck of back in those days when my ride got 9 miles to the gallon downhill and with the wind behind me,,,,,,lol,,,,I really do thank all you guys for trying to help me though, I just don't want to become one of those "today mechanics" whose fix it by replacing parts till they get the right one,,,,,,,lol Chuck

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Probably not...I am not sure what causes this problem but every old body style (1973-1985 and -1991 blazer/suburban/CC) truck I have ever driven has been a little off. In most cases about a quarter tank off.... Since I never let it go below 3/4 tank (the only way I can forget it will cost close to $100 to fill it up...) I am not too worried about running out of gas. If you replace the sender, run a dedicated wire and the aftermarket gauge you should be golden. In honesty, I think it is resistance in the additiative resistance of the associated quick disconnect connections in addition to inaccuracies in the sender. If you can rewire the new gauges with new dedicated wires to the engine, then you can be sure they are accurate.
good luck, mark
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Well when the new gauges go in I do plan on freshening up all the related wiring, so hopefully I'll be good to go.
I did notice that from E to F on the gas gauge is usually like 16 gallons. Apparently, that size tank wasn't even an option. Later I let it go too far, but didn't run out of gas. It took 19 gallons.
I always just thought I had a "reserve" :-P
~jp
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Pretty straight forward to test.
Disconnect the wire going to the sender. Pick up a 90, and 45 ohm resistor (or something like a 100 ohm pot). Hook it/them up between the wire and a GOOD ground. At 90 you should read full. 45, half tank, and so on.... the pot you can just run up/down of course.
If that checks out, then pull the sender and hook an ohm meter up to it. Should see the same 0-90 swing through out the arms travel. If you dont get it, you can try VERY GENTLY sanding the arm, and the coils with like 600+ grit paper.

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