Exhaust System, Muffler, & Converter
A vehicle’s exhaust system is designed to direct harmful gases away from the driver and passengers, reduce the emissions the vehicle releases into the environment, control the delivery of hot exhaust, provide information to the vehicle’s computer to improve vehicle performance, and significantly reduce the amount of noise the vehicle makes.
The only component of the exhaust system that can easily be seen is the tailpipe, located under the back of the vehicle. The entire system, however, is actually much larger and more complex. The exhaust system begins at the engine combustion chambers and runs along the undercarriage of the vehicle, eventually ending with the visible tailpipe.
The major components of the exhaust system include the exhaust manifold(s), oxygen sensors, catalytic converter(s), resonator, exhaust pipes, muffler, and tailpipe.
The exhaust manifold is connected directly to the engine and has the job of harnessing the combustion gases into the exhaust system. It is possible, depending on the size of the engine, for there to be two exhaust manifolds. The manifold, comprised of smooth curving passages to improve the flow of exhaust, can be made of steel, aluminum, stainless steel, or more commonly, cast iron. Cracking, warping, and leaking due to broken mounting bolts are common manifold ailments.
All modern fuel injected cars utilize oxygen (O2) sensors to measure how much oxygen is present in the exhaust. From this information, the computer can add or subtract fuel to obtain the correct mixture for maximum fuel economy and optimal performance. In most cases, there are two O2 sensors in a four-cylinder engine. One is located on the exhaust manifold before the catalytic converter. The other is located after the catalytic converter on the exhaust pipe. In V6 or V8 engines there are four O2 sensors. Two O2 sensors are located before the catalytic converter on each cylinder bank. The other two O2 sensors are located after the catalytic converter on respective banks.
The catalytic converter reduces harmful emissions from engine exhaust. The converter, mounted between the exhaust manifold and the muffler, uses a combination of heat and metals that act as catalysts. A catalyst is a metal, or sometimes a chemical, that causes other chemicals to go through a reaction without being affected itself. The inside of the catalytic converter consists of materials such as platinum, palladium, and rhodium. These materials are the catalyst that causes the carbon monoxide and hydrocarbons to react and produce water vapor and carbon dioxide which are much less harmful to the atmosphere.
The resonator is like a mini muffler with less restriction. It is an empty echo chamber the exhaust travels through where the exhaust energy bounces around, resonates, and some of the noises cancel each other out. A resonator doesn’t just remove sound, it changes it to be more acceptable. The resonator can be either before or after the muffler in the exhaust system.
Exhaust pipes connect all the components of the exhaust system. They are designed to route the exhaust in the most efficient way possible as it travels toward the rear of the vehicle, and to keep the hot exhaust away from heat sensitive components in the engine compartment and along the undercarriage of the vehicle. Exhaust piping is usually made of steel, but can be aluminized steel tubing, or stainless steel, which lasts longer due to its corrosion resistance. Connections are generally made with clamps, gaskets, or welds.
The muffler quiets the noise of the engine. There are two kinds of mufflers. One uses baffled chambers to reduce noise. As sound waves move through this type of muffler, they bounce off the baffles and expend their energy inside the muffler, losing force and volume. The other type forces the exhaust straight through a perforated pipe that contains metal, fiberglass, or some other kind of sound-absorbing material. This type of muffler is designed to reduce back pressure, which occurs when exhaust travels back up the pipes toward the engine, and consequently makes more noise.
The tailpipe comes out of the muffler, past the rear bumper of the vehicle, and directs exhaust gases away from the vehicle. Some vehicles may have more than one tailpipe. The tailpipe often ends with just a straight or angled cut, but may include a fancy tip. The tailpipe is often larger in diameter than the rest of the exhaust system. This produces a final reduction in exhaust pressure, and is sometimes used to enhance the appearance of the vehicle.
The worst enemy of an exhaust system is corrosion, more commonly known as rust. Moisture or water vapor is present in the exhaust as a by-product of combustion and the catalytic converter. Corrosion may also result from outside elements such as rain, snow, and salt. If you live in an area where road salt is used during the winter, make sure to wash the underside of your vehicle with water every few weeks. Salt speeds up the corrosion process and getting it off as soon as possible will help stop the corrosion.
Other symptoms of exhaust system problems may include decreased power, decreased fuel economy, hissing noises, metallic rattling noises, an overly loud engine, exhaust fumes, the presence of a check engine light, and physical damage due to the system hanging low beneath the vehicle.
Many factors, such as climate and driving conditions, can affect the life of your exhaust system. The cleaner the engine runs, the cleaner the exhaust traveling through your exhaust system will be, which will help prevent catalytic converter and O2 sensor failures. It is important to have your exhaust system inspected by an ASE certified technician at least annually, or whenever you experience symptoms possibly related to the exhaust system. Each component should be inspected for damage, rust, leaks, broken bolts, cracks, noises, secure mounting, and to make sure all critical components are present.
If you are buying a used vehicle, make sure the entire exhaust system has been thoroughly inspected before you make your purchasing decision. Having the exhaust system inspected will ensure the vehicle is operating efficiently, will help keep your passengers safe, and may help you avoid costly repairs.