W-124 Fuel gauge problem
 

I have a 1995 E300D. 464xxx miles. Fuel gauge works perfectly until it reaches 1/4 tank. At that point it acts erratically, goes to empty, (as if the power were removed), goes back up to show level.
Once the tank is refilled, works normally again.
I have replaced the sending unit, I have replaced the pod in the instrument cluster with the gauge..... twice.
Any input would be greatly appreciated.
Richard

My thought would be the sending unit in the tank; the bottom always sits in fuel and could be varnished. But if you replaced that... I'm outta ideas!

Probably the fuel sender
 

You have to take the quasi carpeting thing off the rear of the trunk to get to the fuel sender, which is a very big nut. Take that out and the fuel sender will likely have rust and sludge on it. Use a Dremel to lightly shave off the rust from the thin wires, and put it back in, or buy a new one.

I have replaced the sending unit.

I was going to suggest the same as I had the same problem on a GM car. The sender is basically a potentiometer and cleaning the wire wind with Q-tips dipped in acetone cleaned up the varnish and solved the problem, but since the OP said he already replaced the sender and the gage, twice, I'm out of ideas too other than checking that all electrical connections are clean and tight.

A high resistance connection adds resistance to the circle and will screw up the gage readings.

Duke