Topic: Fuel gauge inaccurate

[Captain Kent]

I have posted problems with my 67 200 6 cyl 3 spd instruments in the last 3 months. Temp and press now correct but fuel gauge reads above full with little gas on board.

I tested the gauge following  members instructions ( the gauge tested goes full ) and bench tested the sending unit with success. When sending unit installed the fuel gauge reads above full.

What am I missing? Is it possible when wet the sending unit is shorting?

[RoyceP]

Easy to check. Measure the resistance when the tank is empty. Compare to the resistance when the tank is full. Should be a big difference.

The gage should read zero with the sending unit unplugged. It should peg if you connect the wire to ground.   

[jwc66k]

I have posted problems with my 67 200 6 cyl 3 spd instruments in the last 3 months. Temp and press now correct but fuel gauge reads above full with little gas on board.

I tested the gauge following  members instructions ( the gauge tested goes full ) and bench tested the sending unit with success. When sending unit installed the fuel gauge reads above full.

What am I missing? Is it possible when wet the sending unit is shorting?

The next step you won't be thrilled to do, remove the sender. After over 50 years of the float moving up and down, moving its attached arm on a what can be described as a "coil", that coil wears out. As long as you've got the old sender out, have a new one ready to be installed.
Pics:
The winding - worn.
The wiper arm - worn.
The wiring diagram.
A simple schematic.
Jim

[Captain Kent]

I am now about to install the 2nd new sending unit. Just can’t figure out why sending unit checks out on the bench and doesn’t work when installed. The gauge appears good also. Is it possible that when wet the sending unit goes bad. Also is it possible that the unit isn’t grounded?

[carlite65]

where did you get the sender unit??

[67gtasanjose]

...Also is it possible that the unit isn’t grounded?

Simple to find out, get a wire and temporarily ground the sender.
It should be grounded through the tank and through the senders lock ring but anything is possible

[Captain Kent]

Not sure where I got this sending unit. Restoration over 5 years. Probably had for a year.

[ruppstang]

If you have a second sender plug the wire on it then run a ground wire to the sender frame. With someone in the car work the arm up and down. See if it reads close to correct.

[Captain Kent]

If you have a second sender plug the wire on it then run a ground wire to the sender frame. With someone in the car work the arm up and down. See if it reads close to correct.

I have one and will try that today. Thx

[Captain Kent]

If you have a second sender plug the wire on it then run a ground wire to the sender frame. With someone in the car work the arm up and down. See if it reads close to correct.

I have one and will try that today. Thx

Well I tried your suggestion gauge showed full the whole time. The brand new sending unit made no difference.

So I guess the gauge is bad?

[Captain Kent]

Simple to find out, get a wire and temporarily ground the sender.
It should be grounded through the tank and through the senders lock ring but anything is possible

Tried this, no luck

[ruppstang]

Well I tried your suggestion gauge showed full the whole time. The brand new sending unit made no difference.

So I guess the gauge is bad?

Did it return to empty when unhooked? If you run a ground to sender wire it will show full all of the time. I do not understand how it would do this through the external sender unless you some how grounded the wire.

It is difficult to fix these things from a far. You may be better of getting some professional help.

[Captain Kent]

Did it return to empty when unhooked? If you run a ground to sender wire it will show full all of the time. I do not understand how it would do this through the external sender unless you some how grounded the wire.

It is difficult to fix these things from a far. You may be better of getting some professional help.

I think I found it. I think the new gauge I put in was not quite straight and may have grounded the unit. Worked through it and powered it up. Instead of a full needle it went to E. Checked all the voltage again and couldn’t figure out. But I waited a couple of min and the needle rose just a little. I didn’t wait long enough. So I think through all the process of draining the tank and adding fuel and driving it a bit I may have only 2 gallons or so in the tank.