[spa01s2k]

Engines have a lot of sensors to tell the computer how the car is running. When you put different gas in your car it will change a few different things, such as the amount of fuel going in and spark timing. When you use a lesser grade of fuel (or poorer quality), your engine will run differently and the sensors will pick that up. The computer will then make the correct adjustments to make the car run efficiently, but not as efficient as with better gas.