What wrong with my 2001 E320 start missing each time the gas hand drop below 1/4 in the gas tank?
There is a service bulletin on an inaccurate fuel gauge reading and misfire; it's service bulletin No.: P-B-47.10/23.
Lack of fuel supply due to obstructed fuel supply opening to fuel pump in the splash bow could be causing the problem. If tank level at the time of misfire detection was low (below approximately 1/4), it is possible that the above described condition was caused by lack of fuel entering the splash bowl failing to feed the fuel pump due to foreign material blocking the fuel supply hole (with low fuel level, fuel enters only through supply hole at bottom of splash bowl).
Also the computer system should be checked for any trouble codes to make sure there not any other underlying problem.
If you can't do this on your own then your local Mercedes dealer or local automotive professional can diagnosis the problem for you.