Dancing Gas Guage

[IBChuck]

My '72 has a fuel gauge that is stable when it's sitting still, but when I'm driving will move up and down. At lower speeds the swing is about a 1/4 to 1/2 a tank either way, but it increases at highway speeds and will swing from empty to beyond full. My first thought was the sending unit since it still had the original in it. I replaced the sending unit, but I still have the problem. Thoughts?

[toolboxchev]

I too have the exact same problem. I replaced the sending unit and still have the issue. I also went through and checked all my grounds including the one for the dash.

Same thing, stumped???? Could this be the resistor on the back of the fuel gauge? I might add that I have dash bulb out on that side of the cluster.

Any suggestions out there??? That little bouncy thing is on my nerves......

[Chevyland]

I'll be watching this one!
I've got a truck that does this too.
Hopefully someone has some info

[FirstOwner69]

I had that problem a couple years ago after I installed a used tach cluster. Replacing the gauge with the one from my original cluster fixed the problem. The one that bounced had very little resistance to being rotated. Just blowing on the needle made it spin. The one I replaced it with barely moved when I blew on it. Works like it should now. There is apparently some sort of damping mechanism that keeps the gauge stable as the gas sloshes around in the tank.

[leddzepp]

Follow the wire from your sending unit to the fuse panel. There's a good chance it has a wear spot somewhere along the way, usually under the door threshold guard that it passes under.

[toolboxchev]

Originally Posted by leddzepp

Follow the wire from your sending unit to the fuse panel. There's a good chance it has a wear spot somewhere along the way, usually under the door threshold guard that it passes under.

I will look at this again and report back. May even substitute a new wire in there for positive diagnosis! Thank you!

[FirstOwner69]

I know the wiring is a common problem, but I don't believe the gauge would be stable when sitting still and only bounce when being driven if wiring were the problem. Worth a shot though. Certainly less costly than replacing the gauge.

EDIT: Here's a thread where I summarized my fuel gauge troubleshooting as mentioned in my post above.
http://67-72chevytrucks.com/vboard/s...d.php?t=672327

[IBChuck]

I finally located the cause of the mystery dancing gauge! A PO had replaced the wire to the sending unit, and apparently ran the wire too long. His solution? He wrapped it several times around the dashboard wiring harness bundle by the fuse block. The wrapped wires were acting like a current transformer and current flowing through the harness induced voltage in the fuel gauge wire. I uncoiled the unintended miniature CT, and now the gauge works just fine!

[Stocker]

Thanks for the follow-up (which unfortunately seems to be all too rare)! That sure is one for the books. I doubt many others will have the same problem but ya never know!

[toolboxchev]

This one still has me stumped. I have checked the brown wire from the tank all the way to the fuse panel.

I have decided to wait to look further into the dash at this point. I am still bummed about the ex smashing my NOS gauge I had stashed. UGH!

[VetteVet]

Here's a few from the search.

http://67-72chevytrucks.com/vboard/s...archid=5804654