Fuel gauge trouble shoot help
 

Hello all, I wonder if anyone has seen this particular fault in the Fuel level gauge…
Gauge pegs at full as soon as car is on. If I unplug the sender, at the tank, the gauge drops to empty. Re-plug it and back to full. The sender tested with in the range expected (between full and empty Ohms reading), as did the wire as per factory manual specs. Thing is, the temp gauge also is malfunctioning, though not sure they are related failures.
Any particulars I should look for?
Thanks
Nat

You go through all that trouble and you don't pull the sender out?

http://www.diymbrepair.com/Sender/

Danny

Well, since the resistance measured ok, i started thinking elsewhere...
So if I pull it and test it, might I expect difference test parameters?
I'm new to the Benz and wondered if there were "known" particular issues with this system that might help track it down... Maybe not.
Seems there are other electrical issues too. Better start digging.
Thanks
Nat

After the basics of checking fuses grounds and instrument cluster connections, determine the resistance range of the sender unit and wire up a potentiometer with the same range and attach it to the connector after removing it from the sender. Then turn the potentiometer and see if the fuel gauge behaves as expected.

Be careful to see that there are no fuel vapors in the area where you are hooking up the potentiometer. Make sure you use the center post and an outer post on the pot so that you will get varying resistance.

Good luck,

Thanks Larry, that is an interesting idea.

Ok, so I found that if I maually ground the case of the instrument cluster, everything works like it should. Does this make sense? Is the case of the cluster supposed to be grounded somewhere? How so?

Thanks!
PS. It seems that this is not shown on the wire diagram, or am I missing something?