Gas Gauge Woes

Hello,

My gas gauge reads perpetually at 3/4 full. I pulled out the seat and check the resistance from the fuel level sensor post to the base of the sensor plate. I got 33 ohms which seems about right for the amount of fuel in the tank. However, when I check from the sensor post to any other spot on/around the tank I have no continuity.

I think the tank is not getting grounded properly. There is only the voltage wire going to the sensor, and I don't see how the sensor is getting grounded. Does the ground for the tank depend on metal to metal contact of the tank to the tub?



I'm following these instructions: CJ Speedometer Gauge Quick Test

What should I do to get this system grounded properly, short of installing an aftermarket fuel level sensor with a ground lead? On those aftermarket fuel level sensors with the ground lead, where to you attached the ground lead? Example: More Information for OMIX-ADA 1772404

Thanks in advance for your help - I'd like to get this solved.

 

just a thought...
no all gauge issues are electrical..

chased down a constant "empty" and it ended up the float had a pinhole and filled with fuel....

it looks like you have access... take the sending unit out and see if you can manipulate..

 

The lock ring is supposed to make an electrical connection from the sender plate to the tank. Then the tank grounds to the body, completing the circuit. If you don't have zero ohms from the tank to the sender plate, there is something holding the plate away from the tank. Looking at your picture, I presume this is a late-60s CJ, since they used the lock ring style tank (it would be helpful to put your year/model/equipment in your signature file). There is an o-ring between the plate and the tank, but that should not be enough to separate them.

As mentioned, remove the sending unit and see why there is high resistance between the tank and the sender.

 

Usually the lock ring has a tab on it where the ground wire attaches then runs to the frame. Corrosion build up between ground wire and frame-ground wire to ring tab can cause this problem. Broken ground wire. Rust buildup between lock ring and tank lip will also cause this problem.

 

I'll update my signature. It's a 1970 cj5. Do you think the black undercoating could be hampering the ground?

Should I sand away the black undercoating on a few spots on the tank? The previous owner pulled the tank and under coated the whole thing.

 

Yes. Yes, or run a ground wire as Walt suggests. I have not seen an OEM lock ring with a grounding tab. The factory did not use a separate ground wire, at least for that style of tank. All I've seen is an aftermarket sender with a push-on tab on the plate. If you are good with soldering, you can solder a wire to the plate or the lock ring and run that to the body. That would solve your (presumed) issue with the undercoating without removing any coating.

 

Thanks, I will try soldering on a ground wire. I appreciate the great suggestions!

 

in a manner, of course, that takes in account the explosive qualities of gasoline fumes.

 

Absolutely, PeteL

 

Cool. We'd hate to lose you.