Thanks mpolli for the input.
I'd not had been desperate if it had happened recently.
I drive to work every day the same route and the drop has been observed (the mileage calculated) for a long time, at least 2 months and 6 tank fillings. In the good days I used to reach 200 miles until the half tank mark, now only 160-170 at most.

Benz, it there any sure diagnose for a clogged Cat, I just don't want to blindly replace part anymore.

__________________
1996 E320 since 1/16/08, 171K miles as of Feb 2011

---------------------------------------------------------
1989 300CE - R.I.P. Dec 29 2007
Other MBs (sold): 1992 300E-24 - 1979 350SLC - 1984 230E - 1990 300CE