ASE P2 Test Preparation Guide: Exhaust System

ASE P2 Test Preparation Guide: Exhaust System

WHAT YOU NEED TO KNOW: • Identify major exhaust system components • Identify exhaust system component functions • Identify related items • Provide basic use, installation and warranty information

* Exhaust manifold — Attached to the cylinder head to carry the hot exhaust gases away from the engine. Usually cast iron, but may be welded tubular stainless steel. Manifolds can crack and leak, requiring replacement.
* Head pipe — Carries exhaust from the exhaust manifold to the catalytic converter. Some head pipes may include a small primary “pup” converter to reduce cold start emissions. The pipe is usually stainless steel. Some FWD cars have a “flexible” head pipe to accommodate engine movement.
* Y-pipe — Used on V6 and V8 engines to route exhaust from both exhaust manifolds into a single pipe or single converter.
* Catalytic Converter ­— An emissions control component in the exhaust that reduces pollutants. See the ASE P2 Test Section on Emission Systems. Most vehicles have a single converter, but ones with dual exhausts will have two. Inside is a ceramic or metal honeycomb (or pellets in older GM converters) that has a thin coating of platinum, palladium and/or rhodium. These metals trigger chemical reactions that reduce pollutants.
There are three basic types of converters: “Two-way” converters in pre-1980 vehicles that reduce unburned hydrocarbons (HC) and carbon monoxide (CO), “Three-way (TWC)” converters used in many 1980 and newer vehicles to reduce HC, CO and oxides of nitrogen (NOx), and “Three-way plus oxygen” converters in newer vehicles that have additional plumbing to accept air from an air pump to reduce HC, CO and NOx. Replacement converters must be the same type as the original. Converters for 1995 and newer vehicles must be “OBD II” approved. Original equipment converters are covered by an eight-year/80,000-mile federal emissions warranty. Aftermarket converters have a two-year/24,000-mile warranty.

* Mufflers and resonators — Sound control devices in the exhaust system that reduce noise. Internal baffles and chambers control noise. The muffler may also be packed with fiberglass material to absorb and dampen noise. If more than one muffler is used in the exhaust system, the second one is usually called a resonator because it tunes out specific sound frequencies.

 Many original equipment mufflers are made of stainless steel to extend their life. Most aftermarket replacement mufflers are galvanized or aluminized steel to reduce cost, though stainless steel performance mufflers are available for many applications. “Direct fit” replacement mufflers look and install the same as the original. “Universal” mufflers fit a wider variety of applications and may require adapters to install. Performance mufflers are less restrictive and reduce backpressure for improved power and fuel economy, but may not provide the same degree of noise control as a stock replacement muffler. Most mufflers fail from the inside out because moisture in the exhaust causes internal corrosion.

* Exhaust pipes — Carry the exhaust from the converter to the muffler. Many late model original equipment pipes are stainless steel for extended life. Most aftermarket replacement pipes are plain steel or aluminized steel to reduce cost.

* Tailpipe — The last pipe in the system, which caries exhaust from the muffler or resonator to the rear of the vehicle. May be part of the muffler or resonator on some vehicles.

* Clamps — New clamps are always needed when replacing mufflers or pipes. Clamps come in different sizes and must match the diameter of the pipes or connectors.

* Gaskets and seals — Used between the cylinder head and exhaust manifolds on many engines, and between pipe connections. Must be replaced if leaking or when replacing exhaust components.

* Hangars — Support the pipes and mufflers. Replacement hangars may be needed if the original hangars are missing or broken.

* Heat shields — Metal shields that surround pipes or are mounted between the pipe and floorpan or other components to reflect heat. Loose or cracked heat shields can cause rattles.

* Exhaust tools — Such as pipe cutters and pipe chisels for separating corroded pipes and connectors, and expanders for repairing or installing new pipes and mufflers.

* Exhaust tips — Chrome, stainless and aluminum dress-up accessories that can be installed to customize or enhance a vehicle’s appearance.

Pipes and mufflers don’t last forever, and eventually rust out. A leaky exhaust system is dangerous because deadly carbon monoxide fumes may enter the vehicle. Pipes and mufflers do not require a lot of skill to replace, but must usually be cut apart to remove.

Proper positioning and support is important to prevent annoying rattles.

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