I was wondering if anyone has any ideas as to why I am only getting roughly 15 miles to the gallon, I've been told I am supposed to be getting roughly 30 miles to the gallon. I drive the car like normal, I don't beat on it or anything... I took it to the dealer I bought it from they said to do a fuel injector flush, get a new fuel filter and that should improve the mileage drastically. It didn't improve at all. Then the check engine light came on, I was told it had something to do with the ESG valve, changed that and some other part that connects to it and was told that would also improve gas mileage drastically... it hasn't. The person who had the zx3 before me put a muffler (tip) on and the people at the dealership say I need to go back to stock because I am not getting the right amount of back pressure that is needed at low speeds so the car is having to work harder to speed up therefore using more gas... I am told by others that the muffler has nothing to do with gas mileage. I am confused if someone has any information on what the problem could be it would be greatly appreciated, especially since gas prices are going up : ) (Ford Focus zx3 2001 43,000 miles).