There’s more to your car exhaust system than just your muffler. Your exhaust system safely moves hot exhaust from your engine to your tail pipe, treats it to remove harmful pollutants and muffles the engine noise. Exhaust gas is poisonous, so if it leaks into the passenger cabin it can make you sick or even kill you. Exhaust gas also contains pollutants, but the catalytic converter in your exhaust system scrubs some of those harmful substances. However, catalytic converters wear out and need to be replaced, but they’re expensive, so you want to help them last by keeping the fuel system clean.