Fuel Sender problem. How to test?

[Lippy]

So, my fuel gauge only reads a little over half when I fill it up. I'm assuming one of the fuel senders is bad on one of the pumps.
What is the best way to test which sending unit it is? I have a 88 325i convertible and it looks like the 2 are different. I just need to figure out which one I need to buy. Thanks!

[McGyver]

I did some of reading wasn't able to get a definitive answer.

The two level senders work by changing the resistance as the float goes up/down with the fuel level. I think each should be 0-3 Ohms when full and either 35 or 70 Ohms when empty. Pull each out, test the resistance right side up (empty) and upside down (full). One of the floats may be stuck and just needs a cleaning to get moving again.

wedophones.com has all the wiring diagrams:

http://wedophones.com/BMWManualsLead.htm

I didn't see a spec in the Bentley

[reelizmpro]

First did it happen suddenly one day? Or was it like that when you got the car?

[Lippy]

First did it happen suddenly one day? Or was it like that when you got the car?

It was like that when I bought it in May.

[Lippy]

I did some of reading wasn't able to get a definitive answer.

The two level senders work by changing the resistance as the float goes up/down with the fuel level. I think each should be 0-3 Ohms when full and either 35 or 70 Ohms when empty. Pull each out, test the resistance right side up (empty) and upside down (full). One of the floats may be stuck and just needs a cleaning to get moving again.

wedophones.com has all the wiring diagrams:

http://wedophones.com/BMWManualsLead.htm

I didn't see a spec in the Bentley

Cool, thanks for the info.

[Lippy]

I let this go over the summer and fall while I was still driving the car, but recently started digging into this issue again.
My gas tank is mostly full. I tested the resistance of both senders in the tank and one was 9 ohm and the other was 9.9 ohm, which seems pretty close based on how much gas is in the tank.
I'm not sure what to do. Maybe the senders are fine and the gauge is the problem? Thoughts?

[tomstin]

As I recall, there are two different fuel gauges. I pinched the needle on mine when I had the cluster apart to replace the speedometer gears many years ago. Bought a fuel gauge off eBay. Ran out of gas going to work when the gauge said half a tank. Reach out to http://www.bavrest.com/index.html to see if they can provide any insight.