Gas gauge stuck on F after getting gas
 

71 T37

I only put $20 gas in, gauge was on 1/4 left before. Comes out to about 5 gallons, and when I went to drive off the gauge was on Full. Don't know what happened. Strange thing is, even after I pulled the battery it's still on F, so I guess it's not electric related?

Just out of curiosity, If it's completely full tank, would it stay on F all the time, even with no electric? Or do I have a bad gauge?

GM gas gauges would often remain at the 'key on' setting or drift a little bit after the ignition is turned off.
I always thought that was strange, coming from a Ford ownership background where the gauge always went to empty when the ignition was off.

Check you sender ground 1`st. Black wire that bolts to the car underside somewhere.

Total ground = empty.
NO ground = full, to past full.

Would it be a ground issue though if the battery is disconnected?

Yeah. You will have no grounds with the battery disconnected.

So basically if there was no electric it would be pegged on Full, and grounding it would make it go towards empty in varying degrees?

No. It won`t move with no power. The sender varies the ground with power applied to the gage. You can ground the tan wire on top of the sender. With the key on, the gage should go to empty.

Is that ram wire in the trunk with a plastic connector?

Meant tan wire

Yep. Ground the side that goes back to the front, with key on. Watch gage. Should go to E. If not, the troubleshooting begins.;)

If it does, then most likely, the sender is bad or the black wire, that I talked about earlier, has a bad or dirty connection to car chassis, or tan wire has problem between trunk connector and sender.

I'm taking a wild guess on this, but since it happened right after I got gas maybe it's a stuck float? If it was, would it correct itself at some point by changing the gas level ?

Anything`s possible in an animated cartoon.:)

Sorry for hijacking this but i have a related problem. My gauge reads ok unless i have lights on. Then it reads constantly full.

Grounding problem. Check for body to engine ground, dash ground behind the cluster, etc.