Fuel Gauge Question

[AllardK3]

Hey Guys, I am stumped on this one. My fuel gauge went to full while driving with actual fuel level at about 1/4.

I pulled the sender and it checks out per the manual. 76 ohms Empty 5 ohms full.
The wires from the sender to the gauge check out.

When I unplug the sender the gauge reads empty, but when I plug it back in it immediately reads full regardless of the actual fuel level.

The oil level reading works fine.
Gauge is from an 81 SC.

Any ideas appreciated.

Cheers,
Mike

[T77911S]

its probably the gauge based on the fact you said it is empty when not connected and full when connected.

I would try 2 things
1 check the resistance of the gauge. I would check it from where power comes in to the connection that goes to ground and I would check from power in to the connection to the sender.
then I would compare it to the oil level gauge unless you can get someone to check a known good one.

the above may or may not prove anything unless you can compare to a known good one.

2 you can try this, with the sender out and connected to the gauge, slide the float up and down to see if it changes at all.

my $$ is on the gauge.
if a wire was shorted to ground it would read full when not connected to the sender.

[AllardK3]

T77911S
Thanks for the ideas. With the sender out but connected the gauge still does not respond. (Except the low fuel light works as intended)
With the sender out but hooked to an ohm meter it measures as it should.

I checked the gauge resistance. Fuel gauge is 120 ohms from signal lead to ground. Oil Level gauge is lower, closer to 97 ohms from signal to ground.

Is there something that usually fails inside the gauge, and is it something one can repair themselves?

Thanks!
Mike

[T77911S]

i don't know about the innards of the gauge for sure since I have not taken one apart....yet.

the gauge has 2 coils in it. I suspect one coil is bad.

if you put the meter on the connection for power then check the other 2 connections, they should read different. if they are the same then one coil is bad.

you can also check solder joints inside the gauge.

check the ground at the gauge.

I suspect the gauge wire and the ground will read the same, either open or shorted. if open , check solder connections.