For your mercedes, I would suggest taking a look at some of the mpguino diesel threads, you will be in for some pretty serious experimentation at least:
http://ecomodder.com/forum/showthrea...tion-6778.html
Or the "carbureted mpg monitor" thread might give you some ideas as well.
http://ecomodder.com/forum/showthrea...gine-1123.html