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ASE P2 TEST PRIMER: Exhaust System


10/18/2013
By Larry Carley

Exhaust leaks are dangerous because of the risk of carbon monoxide poisoning. Leaks may occur in mufflers or pipes due to rust or damage, at pipe connections, or where the exhaust manifold mates to the cylinder head. Cast iron exhaust manifolds may also crack and leak exhaust.
 

The exhaust system includes the exhaust manifold, head pipe, Y-pipe (if used), exhaust pipe, crossover pipe, tailpipe, muffler, resonator, catalytic converter, clamps, hangars and heat shields. Most original equipment pipes and mufflers on late-model vehicles are stainless steel (for long life), while most aftermarket replacement pipes and mufflers are less-expensive plain steel or coated steel.

Exhaust leaks are dangerous because of the risk of carbon monoxide poisoning. Leaks may occur in mufflers or pipes due to rust or damage, at pipe connections, or where the exhaust manifold mates to the cylinder head. Cast iron exhaust manifolds may also crack and leak exhaust.

When replacing or installing an exhaust manifold, new gaskets and bolts should be used. When replacing a muffler or exhaust pipe, new clamps are usually necessary. Missing or damaged hangars and heat shields also should be replaced.

On Front-Wheel Drive (FWD) cars, the head pipe that connects to the exhaust manifold may have a flexible section to accommodate engine motions. Over time, the flex section may weaken and fail creating an exhaust leak. Repair flex sections are available for some applications (requires welding to install).

Some head pipes on late-model vehicles contain small “pre-cats” (mini catalytic converters) that heat up quickly to reduce cold start emissions. The converters are part of the pipe and cannot be replaced separately. The catalytic converter is mounted behind the head pipe. There are different types: “two-way” converters for pre-1980 vehicles that reduce unburned hydrocarbons (HC) and carbon monoxide (CO), “three-way (TWC)” converters for many 1980 and newer vehicles that reduce HC, CO and oxides of nitrogen (NOx), “three-way plus oxygen” converters that have an air pipe to inject air into the converter, “OBD II” converters for 1996 and newer vehicles, and “CA-approved” converters for California vehicles. Replacement converters must be the same type as the original.

Mufflers and resonators typically rust from the inside out due to moisture and acids in the exhaust. Replacement mufflers include “direct fit” (same dimensions and fittings as the original) and “universal” (which often require adapters and some modifications to install). Performance mufflers offer reduced back pressure for better performance and fuel economy, and a more powerful sound.

Required to pass this section of the P2 test:
1. Identify major exhaust system components.
2. Identify component function and common reasons for replacement.
3. Identify related items, including exhaust hangars, clamps and heat shields.
4. Provide basic use, maintenance, installation, and warranty information.















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