recently i have noticed that the gas mileage of my hatch has droped a fair bit, and also my exhaust tip gets a black build up on the lip (i wipe it off drive to school and back and its covered in it again) i dont know if thats normal or not and if these two are realated, i checked the oil and its good. so yeah anyone please give me some insight on why A) my gas mileage went down or B) why i have that black deposit on my tip....thanks