I have a '92 Mustang LX hatchback (4 cylinders). I've only had it for 4 months. It uses a ton of fuel. I drove 50 miles the other day and it used almost half a tank of gas. It uses significantly more fuel at highway speed than in the city. Does anyone have any ideas of what I can check to fix this problem? I'd prefer to try some things myself before spending hundreds of dollars taking it to a mechanic, but I don't know where to start.