Faulty Fuel Gauge

[BoattailLou]

Hello,
Could use some help with my faulty fuel gauge on my 71 Riviera.  When I disconnect sender wire (hot) at rear trunk gauge goes to "F" or above.  Now, when I use a jumper on this same wire and ground it gauge goes to "E."  I then ran resistor tests with different values to mimic the sending unit.  The results were"  22ohms = just above "E", 47ohms = 1/4, 68 ohms = 1/4, 100ohms = 1/2
Now, I am lead to believe the problem is forward from sender wire to the fuel gauge.  Would the problem be bad gauge or somewhere in the wire to the gauge.  I would like to find out before I take the gauge out to inspect.  Thanks for your time

[EmTee]

On 3/19/2022 at 10:25 PM, BoattailLou said:

When I disconnect sender wire (hot) at rear trunk gauge goes to "F" or above.  Now, when I use a jumper on this same wire and ground it gauge goes to "E."

That ^^^ tells me the problem is with the sending unit, or adjustment of the float arm.  In any case, the gauge and wiring seems to be working as designed.

[Bloo]

Well yes but wait a minute. @BoattailLou , what is the exact problem with the gauge when everything is hooked up and you are driving the car? Too high? Too low? Not working at all?

 

A 1971 GM gauge should be 0-90 ohms. I would have expected the 47 ohm resistor to read something closer to 1/2 tank.

[EmTee]

Maybe I'm misunderstanding the post, but I'm assuming that the following resistance values were measured at the sending unit with an Ohmmeter.  If so, then it seems the variable resistor is faulty, or dirty?  In any case, the issue sounds like it lies with the sending unit.

 

On 3/19/2022 at 10:25 PM, BoattailLou said:

The results were"  22ohms = just above "E", 47ohms = 1/4, 68 ohms = 1/4, 100ohms = 1/