Funky Fuel Gauge

[Baileyboy]

Hi Guys, The fuel gauge on my 70 Dart recently worked for a day or two. Now, nothing again. It has not worked for the three years that I've owned the car. I thought it was the sending unit. But, when it worked earlier this month my theory went out the window.
Any ideas where I should start?
Thanks for the help in advanced.

 

[jonnydart440]

Probably still the sending unit. Mine was broke in such a way that the resistor would fall away from the contact on the float rod and not work for a while then fall back in place and work.

 

[jonnydart440]

What ever u do, DON'T ground the fuel sender wire to see if the gauge jumps, you'll blow some resistor thing in the cluster! That's what I did, I'm sure someone else scan chime in and explain it better, bit just be careful!

 

[RedFish]

If the temp gauge works without similar faults, 2 possible issues in fuel gauge circuit alone,
Ground jumper at sender loosing connection due to rust.
Loose gauge. To explain, The stamped tin speedy nuts that support gauge also connect it to the printed circuit board. The contact/mounting studs on these instruments are swedged into a thin piece of fiber board. That and the hollowed out tin nut designed to absorb vibration for 50 years. Times up LOL. Seriously, A lot of owners have replaced the speedy nuts with real hex stock hardware. I wont recommend that. The fiber board on the gauge might shatter like a soda cracker.
One other less likely possibility is a loose contact pin where the wires attach to the board. Loose and/or broken pins most often occurs when the female harness connectors are pulled on.
If this instrument panel has been removed and reinstalled before, the loose pin is more likely.
Bottom line, Sender is always first suspect and inspect simply because its easiest to access.

 

[Bull1tt]

You Can do this, just be careful...

What ever u do, DON'T ground the fuel sender wire to see if the gauge jumps, you'll blow some resistor thing in the cluster! That's what I did, I'm sure someone else scan chime in and explain it better, bit just be careful!

With key OFF, disconnect the wire from the fuel tank sending unit. You need to ground this wire to the body, making sure you have a good connection. Turn your key on to 'run', and watch the fuel gauge. If it sweeps towards "full", turn the key OFF! Your sending unit is at fault and your dash gauge and wiring are good.
If it doesn't move, it may be the voltage limiter or the gauge. If your temperature gauge works normal, your limiter is working. It's either the gauge or a bad/broken wire. If you remove the instrument cluster, you can check the gauge with a couple 'd' cell batteries in series. They are 1.5 volts each, so connecting them to your gauge should make it read half-tank on 3volts. Your limiter lets the dash gauges operate on 5 volts. Any more voltage will ruin the gauge. If gauge works, check circuit board on cluster. Then the wire, that's all there is.

 

[Bull1tt]

There is a metal clip on your fuel tank sending unit that grounds it to the fuel line. Make sure that your sending unit is grounded. Your gauge reads the resistance that sending unit sends to ground.

 

[Baileyboy]

There is a metal clip on your fuel tank sending unit that grounds it to the fuel line. Make sure that your sending unit is grounded. Your gauge reads the resistance that sending unit sends to ground.

Thanks for the advice!

 

[Baileyboy]

There is a metal clip on your fuel tank sending unit that grounds it to the fuel line. Make sure that your sending unit is grounded. Your gauge reads the resistance that sending unit sends to ground.

Thanks for the help!

 

[Baileyboy]

There is a metal clip on your fuel tank sending unit that grounds it to the fuel line. Make sure that your sending unit is grounded. Your gauge reads the resistance that sending unit sends to ground.

Thanks for the idea!

 

[Baileyboy]

There is a metal clip on your fuel tank sending unit that grounds it to the fuel line. Make sure that your sending unit is grounded. Your gauge reads the resistance that sending unit sends to ground.

Good advice, thanks!

 

[Baileyboy]

Probably still the sending unit. Mine was broke in such a way that the resistor would fall away from the contact on the float rod and not work for a while then fall back in place and work.

I will check it out!