I am new to mustang's so bear with me, but When I get out of the car to run into the house, or when I'm warming it up, the exhaust fumes are really horrible, like I'm driving an old truck, but none of the smells get into the car so I havent worried, but is the strong smell normal for a car without cats? The other thing I thought may cause it, the tune for my car is for 93 octane gas, but no gas stations here sell 93 so I have been using 91 could this mess anything up?