Automotive Q&A

Learn about your Exhaust System

Exhaust Inspection – What is it?

An exhaust inspection is a very simple, but very critical service. The inspection includes a visual examination of the exhaust manifold to the tail pipe. All parts in between, including the catalytic converter, muffler, and pipes, are inspected. An exhaust inspection is required to control your vehicle’s emissions and to make sure your vehicle will pass an emissions test. In a typical four-stroke combustion engine your engine goes through four phases: intake, compression, combustion, and exhaust. During the intake stroke the intake valve opens, while the piston moves down, and allows air and gas to mix in the engine. Next, in the compression stroke the piston moves back up to compress the air/fuel mixture. In the combustion stroke your engine’s spark plug ignites the air/fuel mixture, while the piston moves down. Finally, during the exhaust stroke the piston moves back up as the exhaust valve opens to let the air/fuel mixture enter the exhaust manifold and travel through the exhaust system. The exhaust manifold, the first part of your vehicle’s exhaust system, is attached right to your engine. The fuel/air mixture from all of your engine’s cylinders, whether you have a four, six, or eight cylinder engine, will end up in an exhaust manifold. The manifold receives the burnt engine gases and will completely burn any unused or incomplete burnt gas. The manifold also houses the first oxygen sensor in your exhaust system to inspect the amount of oxygen entering the system. The oxygen sensor monitors the amount of oxygen and will tell the fuel injection system to increase or decrease the amount of oxygen used in the fuel/air mixture used to power the engine. The sensor also makes sure there is enough oxygen in the exhaust system to be used by the catalytic converter. The manifold then sends emissions through the exhaust pipes and into the catalytic converter.Your engine produces many harmful gases, which the catalytic converter must control. Catalytic converters contain substances or compounds such as platinum, rhodium, and palladium that react with, and convert, these harmful emissions. Catalytic converters react with, and convert, harmful gases such as carbon monoxide, hydrocarbons, and nitrogen oxides produced by your engine into less harmful gases before they travel out your exhaust system and into the air. Once these harmful substances travel through the catalytic converter, the exhaust pipes send the emissions into the muffler.Your vehicle’s muffler aids in dampening emissions as well as engine noise. Mufflers are mainly used to dissipate the loud sounds created by the engine’s pistons and valves. Every time your exhaust valve opens, a large burst of the burnt gases used during your engine’s combustion is released into the exhaust system. This release of gases creates very powerful sound waves. Finally, once your engine’s emissions travel through the muffler, they are released into the atmosphere through your vehicle’s tailpipe. During an exhaust inspection, all of the exhaust system’s parts are visually inspected for any cracks or other damage. All of the clamps, mounts, and gaskets are also inspected. Then each exhaust system part (exhaust manifold, catalytic converter, muffler, pipes, and tailpipe) is checked to make sure it is working properly and controlling your engine’s emissions.