i usually get about 12mpg if i baby it (shift at 2000-2500rpm) and i thought that was bad. me and my girlfriend took my dog to petco for something to do on saturday. it was about a 110mile round trip and i put in 15.4 gallons of gas and ran out of gas when i was about 3 miles from home. how could i all of a sudden get 5mpg worse? all of this driving was at highway speed. i have a new air filter and new spark plugs.

 

Sounds like either a fuel leak, leaking fuel injectors (if so equipped), dragging brakes, way low tire pressure, or the dog is a St Bernard.

 

clogged exhaust.