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I am rebuilding my 69 and I just installed my dashboard. All the components are working correctly except my gas gauge. When the key is out and the car is off the gas gauge is on full, then when I turn the car on the needle goes past full...any ideas why this is happening and how to fix it?
 

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The tank is full, just drive it around a little. Sorry just couldn't lay off that one.
It looks as if the gauge has power. The gauge changes reading through the ground circuit. If memory serves, grounding the wire to the sender will make the gauge show full. As the fuel level falls, resistance to ground in the sender increases and the gauge moves toward E. Your sender wire may be grounded somewhere.
 

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Actually an open in the wire to the sending unit or no ground from the unit to the body the gauge will go past full. If fully grounded goes all the way to the left past empty. Check the ground wire coming from the top of the tank (black) going to the body or chassis. Remove where it is screwed on and clean everything. Let us know what that does.
 

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check your dash grounds.if you unplug the pink wire from your tank the gauge should go empty,ground it it should go full.if unpluged it still reads full check the wireing under the dash.you have trhee wires to the gas gauge .an ignition hot a ground,and the sender wire (pink)
 

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Carl, you also have it backwards. Unplug either wire at the tank and the gauge goes full right past full. Fully ground either wire and it goes to empty. Try it.
 

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I've had a problem with my gas gauge since I got the truck. Regardless of how much gas was in the tank, it was never accurate. A full tank read about 1/4 on the gauge, and went down from there. I never saw more than 1/4 on the gauge.

I just pulled the whole tank down and disconnected all the wiring. Now, when I turn on the ignition the gauge goes all the way to full. This means the gauge itself works, right? When I connected the tan wire to a chassis ground, the gauge goes all the way to empty. What does this likely mean - that it's ground wiring? Or possibly the sender itself?
 

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This is frustrating. I dropped the tank and pulled the sender, and it looks quite new (definitely not 43 years old!). I connected a multimeter and the sender is putting out 0 ohms and 90 ohms when it should. I hooked everything back up with a new ground wire and reinstalled the tank.

Then I put about 8 gallons of gas in, and the gauge is still below 1/4 full :( I think I may have a miscalibrated, or broken, gas gauge. I'll see if I can find another one to test with.

The other thing I can do is find a variable resistor and see what resistance I need to apply to get the gauge to go to totally full. My guess is that it's going to be more than 90 ohms. :let_it_all_out:

One other thing I noticed is the gas gauge stays in the same position even when I turn off the ignition.
 

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the gauge sounds like its working,
:dontknow: could the float arm be bent or hanging up,, or the float is sunk?? :texas:
Well, the gauge "works" in so far as the needle moves freely from full to empty. But, without knowing how much resistance it takes to move from one side to the other, I don't know if it's working the way it's supposed to.

The float arm was operating very smoothly, from what I could tell the sender only seemed a year or two old. I re-installed it correctly, I don't think the arm is hitting the side of the tank or anything.
 

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I have a 77. Fuel gauge is pegged past full. If I unplug the tan wire coming from the top o the tank, and touch either end to bare metal, the guage still does nothing. Sender of gauge?
 

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Also having a gas gauge issue.

My gauge was erratic bouncing around and often getting stuck on full when it was near empty. I bought a new sender unit and took it to a local shop to have it installed. The shop charged me $120, so I felt that was money well spent since I don't have lift.

The shop called and said the sender was in, but now the gauge doesn't work at all. They also ran new wire and now they are sure it is the gauge itself. I have a 71 and the sweep style. I can't find one of those gauges anywhere.

Any thoughts?

Thanks
 

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Hopefully the sender in your '77 is OK Scott...hard to find a new one.....if at all...

I seem to remember that older GM tank gauges & senders were 0 to 30 ohms, and not 0 to 90 ohms like the later models.....
Not sure what year they changed...

If that is what is supposed to be in that '69 Elco, then a 0 to 90 wont work, ( or it may read 1/4 ):smileyb:
 

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Wow this is an old thread from when I first joined. I think I started my own thread later. I'm not exactly sure how my gauge started working. The truck had sat for a while before I bought it so on the way to my first car show, I put in a bottle of STP carb cleaner and drive about 80 miles, stopping frequently to top off the tank with fresh gas since I had no idea of my consumption.
On the way back from the car show, I noticed my gauge was working. It was possible old gas had gummed up on the sending unit spring and other parts causing a bad reading.
I had not fooled with the ground but I did unplug and clean and plug back in the wire harness that goes through the quarter panel behind the side marker light.
The wire harness wires did have some of the plastic coating peeled back and I wrapped each wire too, perhaps contact among wires was the issue but the pink gas wire had its own plug.

I have since installed a new wire harness and had the gauge te painted and calibrated.
I have pics if anyone needs them
 
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