Fuel gauge stays between 3/4 and Full

[tkruger]

1987 Monte Carlo 4.3 original tank etc.

Fuel gauge was working fine. Filled the tank till it clicked off and since then it only moves between 3/4 and full. To make matters worse when the car is moving the gauge will move up from 3/4 to full all the time. When it is at idle it may drop as low as 3/4 if the tank is not full. Other than an issue in the tank is there anything I can check to troubleshoot this? Are there any common causes for this problem?

 

[Built6spdMCSS]

Sounds like the thin wire on the float is broken or the contact is dirty.

 

[rfpowerdude]

Sounds more like the float gets stuck and doesn't drop after it goes below 3/4 full. I bet if you drop the tank and pull the float, it is probably sticky at that level.

 

[Built6spdMCSS]

Yup that too. It'll have to come out anyway to troubleshoot.

 

[tkruger]

I was afraid of that. Not dropping the tank with a month to go in the season. Just have to keep track of the miles I drive for now I guess.

 

[SS_Malibu]

When you do drop the tank put a new one in it and be done with it. At least that’s what I would do.

 

[rfpowerdude]

There's also the possibility that the float came loose and the potentiometer/rheostat is hanging loose and when the fuel goes below 3/4, the float itself is hanging down and the potentiometer won't go below 3/4 due to a hanging angle.
Either way, you're right, no way to get around fixing this without dropping the tank.

 

[Bonnewagon]

The fuel level sender works by resistance. You can test with an ohm meter to see what the values are. My 1983 Pontiac FSM says resistance at full is 80 ohms, 0 at empty. Of course check the wiring and grounds first, but test and see if dropping the tank is necessary.

 

[SS_Malibu]

I think when I bought my AutoMeter fuel gauge it was 90/0 ohms for later model GM

 

[Built6spdMCSS]

I would unplug the connector back there and see what the gauge does with the key on. If it pegs out in one direction really far, then it's definitely something on the sending unit.