Hi I am new to the fourm...and I need help! I have a 2004 V6 3.9 mustang. I bought it new and the only thing I have added is a stereo. I have less than 48,000 miles on it. About 3 weeks ago I noticed my gas mileage was really bad. Usually I get 19-22 mpg. It has only gotten about 10 mpg last two fill ups so we changed the air filter( it wasnt dirty) to a K&N..but that didnt help. Its not showing any codes, starts fine ,runs fine and yeah even though its a 6 cylinder I have to get into the gas every now and then but not that much! Any ideas? (My other fords..I expect bad mpgs 1982 Bronco V8 & 1990 F150)