bad gas milage

[anamandy]

I have a '96 Century that I got in early July. For the first few weeks I had good gas milage but now it's gotten terrible. The previous owner was an old lady who drove it very slow. She also was up on her maitenance (oil change, belts, tune-up, brakes, etc. ) This car was in excellent shape. But I drive the car differently, doing a lot of highway driving (55-65)and high elevation driving (I have to climb a mountain every day), and I guess this car is not used to that. Should I use a fuel injection cleaner? Just a note, when I do climb the mountain, this car never has a smell. My other car went through 2 Catylatic converters and always smelt like rotten eggs or a greasy smokey smell.
Also, one other question. does anyone know exactly how much gas this tank holds? I'm not sure because I never let the tank get empty. Thanks for any info, Mandy

[GTP Dad]

Fuel injector cleaner can't hurt. It will clean the injectors for you and possibly improve your gas mileage slightly. As far as the other issue, if this lady drove slowly it is possible that the Oxygen sensor is going bad slowly. Have it replaced especially since you do a lot of high altitude driving. If it is not reading the O2 in the exhaust properly it will allow more fuel into the engine and cause the mileage to suffer. As for the rotten egg smell, the older convertors had this odor but the newer designs have eliminated this, don't worry about the absence of a smell. Sorry I don't know what size the tank is!