Erratic Fuel gauge / Secondary Fuel Sending Unit

[grahamsy2k]

My fuel gauge isn't working properly and I'm trying to figure out why. Yes, I've checked the nut on the back of the cluster lol. It's an 88 so it has the two fuel sending units wired in series.

Using a DMM I think I've narrowed it down to the driver side unit. Testing it empty and sitting in some fuel it gives me around 20ohms. So it's not fluctuating. If I'm understanding it correctly it should fluctuate with respect to how much fuel is in the tank, correct? Similar to passenger side one. So I'm thinking its broken.

And if it is working properly, should they both give the same reading?

http://wedophones.com/Manuals/BMW/1988%20BMW%20325%20-%20325i%20-%20325is%20Electrical%20Troubleshooting%20Manual.pdf

Here is what I'm using. page 6210-1

[dnguyen1963]

The floater inside the sending unit can be stuck (mine was). I cleaned with with carb fluid. Spray the carb fluid into the sender and shake the floater up and down vigorously. You'll most likely see a lot of black debris coming out. Keep doing it until the floater can move freely without any resistance. Your fuel gauge reading should be much more accurate after the cleaning.

[grahamsy2k]

I was able to test a functioning unit and confirmed that the resistance is suppose to fluctuate. And has a similar range of 0~60 ohms

I tried cleaning it to no avail. So I decided to take is apart and see if I could fix it. Turns out there are two thin wires connected to either end of the circuit on the top. They both run tightly down to the bottom and connect. The float is guided by these to wires and has a little metal piece to create a circuit. As the float moves up and down, the circuit either gets shorts or longer.

In my case, the wire had snapped and twisted. Which is why I was getting on constant reading.