Yet another fuel gauge one... what's wrong?

[Mopewbie]

Right, I'll try to cover ad much as I can:
Tested fuel gauge straight to negative, it works fine going all the way up.

There is a dedicated ground from chassi to fuel sender unit to make sure it has good ground.

Sender if giving me the right range, 10 (or so) on full, 75 (well, 77) on empty.... reading all the way through.

When testing it, it won't give any reading apart from FULL.

I connected a ground wire and the wire to the gauge and onfe inside the car I'm moving the float in the sender but nothing, only it I go all the way up "full" it will give reading, once I go down a bit, half way, gauge goes down to hiding the needle.

Can it be the gauge since I have earth, wiring seems to be working fine and sender seems to be giving the right ohms?
Tried with 2 sender units by the way.
Or still be the sender?


Thank you.

 

[Mopewbie]

More pics, full at "full", empty when moving halfway or less.

 

[68-500]

ya. Does the sender seem to read linear when you slowly cycle it while’s it connected to multi-meter? If so Id suspect wiring or gauge itself. Maybe there’s a problem in the cluster?

 

[Gold Rush]

It appears to me like the sender you show tests good. I agree with 68-500 about the wire or gauge. Where did you have the sender connected while showing the gauge readings? Might need to closely examine feed from sender to gauge.

 

[Beekeeper]

ohm the sending unit again this time take it through the full range slowly and verify that it doesn’t open circuit anywhere through the full range. what you show here
points to the sending unit being faulty. Reading the ohms at full and empty only
doesn’t fully test the the function of the sending unit. If you get good a good incremental change in the resistance value i would call the sender good and look elsewhere as stated above.

 

[bobsgtx]

An old analog VOM is good for testing rheostats or any variable resistor. Watching needle movement is easier than watching constantly changing numbers.

 

[440beep]

I had a similar issue with my 69 Bee rallye fuel gauge. Sender checked out fine as did the sweep test. Sender is also grounded to frame. I took the gauge cluster out, cleaned the circuit board with a brass wire brush, and retightened the gauges. And ta da, my fuel gauge now reads full when full and everywhere in between.

If you can, while laying on the floor under the dash, reach up from the bottom and find the two nuts that hold the fuel gauge in place (forget the size so it’ll be an experiment) and snug the nuts a bit tighter. Don’t gorilla tighten them, just see if they’re snug.

 

[Mopewbie]

Thanks all, I'll try and run some tests.