Gas gauge stuck on Full position

[Edahall]

Vehicle: 1982 Chevy Suburban 6.2 Diesel with 32 gal tank

The gas gauge is stuck on the full position. It used to be that when I would use up approximately 1/2 the tank of fuel, the gauge would suddenly start working. Now the gauge is stuck on full and has not worked for a long time. Based on the symptoms, does this sound like a wiring problem or a sender problem? Is there a way to diagnose the problem without lowering down the tank? Could it be a bad fuse?

[Subzilla]

I'm not real sure how to diagnose your problem. Let the other experts pipe in here. BUT IF you do decide it is the guage, here's a link that might help and save ya some money. Another TDP member recommended it : http://www.fix-a-gauge.com/faq.php#3

[Edahall]

If I let the vehicle sit for a while, the gauge settles at 3/4 tank. As soon as I turn on the key, the gauge goes back up past the full mark.

[Robyn]

You probably have a failed sending unit.

best
Robyn

[Edahall]

It's very strange that I called the local auto parts stores and they said it was unavailable for my vehicle. I then checked online at www.rockauto.com and it also was unavailable. However, if I check for 1984 and newer Suburbans, it is available. Will a sending unit from an 84 Suburban work on an 82 Suburban?

[highpockets]

My gauge reads past full if the sending unit is unplugged. Broken wire or bad connection will cause the same reading. I would look for rust on the sending unit rheostat wire.

[rhsub]

Find wire going to sending unit (I think its tan on an 82 or may be gray), ground wire to frame and turn key on momentarly, guage should go to "E", if not backtrack to guage checking for a bad connection or broken wire. If guage works check that sending unit is properly grounded, if ground is ok you will have to remove tank and repair or replace sending unit. The reostat coil on the sending units are the same in most of the older GM's and with a bit of care you can probably swap it from a wrecking yard unit.
Check unit with a ohm meter (0 ohms empty,approx 100 to 120 ohms full)
Good luck
Ron

[Edahall]

Thanks guys. I got this problem fixed. I started out with Ron's suggestion by grounding the wire to the frame. The fuel gauge went from Full position to Empty position. This test ruled out a wiring problem as well as a gauge problem. The next test was using my meter. I got the following:

Resistance on Sendor (Empty Tank)
Black - 0 Ohms
Yellow - 2 Ohms
Pink - 3.5 Ohms
Pink to Yellow - 13.5 Ohms

Voltage on Plug
Black - 0 Volts
Pink - 8.5 Volts
Yellow 12.2 Volts

There were 3 wires that went to the sender. I'm not sure what the pink wire was for. Anyways, the problem turned out to be a connection problem. I cleaned the plug and connected it back up to the sendor and the gauge started working again.