I was having this problem and desided to take a stab at replacing the fuel injector seals and cleaning all the crud out of the holes where the injectors sit. I went the put the injectors back in and freaked at all the build up around the area of the hole. I was getting maybe 75 miles for the first half tank of gas and after putting new seals in it jumped up to 120 miles per half tank. Even if this doesn't fix the original problem and has not been done for a while it still doesn't hurt to do it.

1991 740 GL non-turbo automatic wagon with 199,000. I get 24-27 mpg on the freeway. I saw a nice couple mpg improvement from a good long hard highway run with fuel injector cleaner in the tank (Techron). Dumped in the bottle, filled up the tank, drove 350 miles of freeway nonstop (I frequently do 600-700 mile drives, so this was easy for me).

You dont mention where you are. Some states (like Kali-4rnia) use winter (or oxygenated) gas - which definitely reduces mileage. In my case - when I moved to the west coast (with my 85 740 n/a), I lost 20-40 miles to a tank of gas.

Noel

Seems that these cars aren't the most fuel efficient. I have a 1990 745T automatic and recently I did a trip from South Carolina to Florida at about 75 mph all the way and I never got better than 22 mpg. Around town I get 18 to 20. Of course I do have a habit of exercising that boost needle quite often. However by contrast I also have a 1997 Lincoln Towncar, almost 2 tons with a V8 and I always get 20 mpg local driving and about 25 on the highway.
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Randy

Take a look inside your airbox. I was having the same problem with my 740 a few years back and when I looked into the Air box I found about 500 acorns in there. You may not find acorns but, you might want to take a look into it. Just for starters. Don't laugh, strange things have been found in air boxes.
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Rich George