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Discussion Starter #1
ive thoroughly looked through past posts on fuel gauge issues, but im still stumped. when i disconnect the wire in the trunk from the sending unit's tan wire, the gauge reads past full. when i then ground that wire, the gauge reads empty. from what ive read, this means my gauge and its wiring are ok. the problem is, when i have the sending unit hooked up and i move the float to empty, the gauge reads empty, but when i move the float to full, the gauge only goes to 1/4 full. is my brand new sending unit bad, or what can be causing this?
 

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Check your new sending unit with a ohm meter. It should read approximately 0-90 ohms. Make sure that the unit is well grounded.
 

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My guage does exactly the same thing you describe. It will read no higher than a quarter of a tank when hooked up but reads full when disconnected and empty when grounded. I too checked previous post and found one where someone described this same scenario and the problem was the ground at the instrument cluster. But my understanding was that the scenario you describe indicates that everything is ok from the guage back to the connection in the trunk. At any rate, I still haven't figured it out. I realize this is zero help but thought I would commiserate.
 

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This discussion may be of some help. Not sure if he ever really found the answer but it has some explanations of the circuit. http://www.chevelles.com/forum/Forum22/HTML/002399-2.html

If you do the test that Mike talks about, getting the odd results like this guy did, good chance it's the calibration resistor on the back of the meter.

[This message has been edited by John_Muha (edited 10-23-2002).]
 

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I had the same problem with my fuel gauge. I cleaned rust and/or corrision from both the male and female parts of the plug behind the fuel gauge with WD 40 and 600 grit sandpaper.I removed the male plugs so I could clean where the studs pass through. Th is cured my problem. Good luck, Jack I found my problem using jumper wires with small alligator clips.

[This message has been edited by smalblock (edited 10-23-2002).]
 

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Discussion Starter #6
well i finally fixed it, turns out i was missing the little ceramic plate that goes on the back of the gas gauge. took one off a '75 impala at a junkyard, stuck it on there, and the gauge reads perfect now. victory, sweet sweet victory.
 

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If that was a square looking thing that went to the terminals:
Sounds like you were missing the calibration resistor. If so that makes sense.
 

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Does anyone know about swapping resistors and the various resistors used?

I replaced the right pod large fuel gauge on my 69 with a center mount small fuel gauge and used the original large gauge resistor. The sending unit is new and all wires are properly installed.

The gauge reads full when the tank is full, but when the gauge hits empty, I still have 1/4 of a tank. Sounds like I need a different calibration resistor.

[This message has been edited by gheatly (edited 10-30-2002).]
 

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Read some of the information in the link I posted above. Try the test that Mike talks about and see how the gage responds. This will tell you if the problem is external to the gage. A poor sender ground or poor gage ground will also cause the gage to read high.
I have heard that the resistors used in small gage mid 70s trucks work as replacements.
 
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