STP 1 Tank Tune-Up Fuel Additive is specially formulated to work both as a fuel system cleaner and an exhaust system cleaner in one single use. This 12 oz fuel additive helps reduce knocking, quiets rough engines and helps eliminate hesitation and hard starts to help your engine run smoothly. The proprietary blend of ingredients is specially formulated to survive high temperatures in the combustion chamber, allowing it to clean the fuel injectors, intake valves, spark plugs, oxygen sensors, cylinder head and piston tops. It also protects and maintains the catalytic converter and improves fuel economy. Even better – this car exhaust system formula reduces up to 50% of hydrocarbon emissions, reducing the amount of harmful exhaust emissions in the environment and helping you pass an emissions test. STP products use advanced chemical technologies to keep your vehicle running stronger for longer. Trust in the science, technology and performance with STP.