C3 Gas Gauge Problem

[Lee S.]

Went out for the Sunday drive yesterday and noticed that my gas gauge was pegged all of the way to the right past the full indicator. The gas tank was full at the time. A little while later it bounced back and forth from full to the far right for a while. Now it seems to be OK.

Any thoughts? Gauge, tank sending unit? wiring? Geez... so many choices. Help!

PS. 1974 Coupe/454/automatic

[Jack H.]

Re: C3 Gas Gauge Problem

I doubt it's the sender, erratic full-scale deflection symptoms typically result from flakey ground connections, there are essentially three places I'd go check...

(1) Does the tank sender have a good ground reference at the tank itself?

(2) Is there visible damage to the wiring harness running to the tank sender (either rubbed insulation causing the sender wire to false ground and bypass the sender's resistor OR the lead wire being fractured inside its insulation and therefore open circuiting will generate 'Jeckyl/Hyde' pointer needle operation)?

(3) Does the fuel gauge have a solid ground reference at the dash instrument cluster? Two opposing electro magnets 'pull' the pointer needle. One has a fixed branch circuit current based on current flow through the electro magnet to ground at the dash. The opposite electro magnet pulling on the pointer needle has variable current flowing through it based on the the circuit path from the gauge, to the tank sender, through the sender's potentiameter, to ground at the tank...