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ASE P2 Test Preparation Guide: Exhaust


10/9/2009

ASE P2 Test Preparation Guide: Exhaust
 

Sample Review Questions:
1. Counterman A says front-wheel drive cars and minivans with transverse (sideways) engines often have a flexible head pipe or coupling to accommodate engine motions. Counterman B says the Y-pipe on a V6 or V8 engine connects the exhaust manifolds to the catalytic converter. Who’s right?
a. Counterman A only
b. Counterman B only
c. Both Counterman A and B
d. Neither one

2. A “pre-catalyst” is usually located where?
a. Between the cylinder head and exhaust manifold
b. In or just behind the exhaust manifold
c. Just behind the catalytic converter
d. Between the converter and muffler

3. A “resonator” does what?
a. Helps reduce emissions
b. Helps dampen vibrations
c. Helps muffle noise
d. Helps reduce backpressure

4. Counterman A says a “cat-back” replacement exhaust system usually includes a new Y-pipe or head pipe, intermediate pipe, muffler and tailpipe. Counterman B says other parts that may need to be replaced when changing a muffler or pipe include clamps, hangars, gaskets and heat shields. Who’s right?
a. Counterman A only
b. Counterman B only
c. Both Counterman A and B
d. Neither one

ANSWER KEY
1C, 2B, 3C, 4B

EXPLANATIONS:
1. A transverse mounted engine in a FWD car or minivan does a fair amount of forward and backward rocking, so the exhaust system must be able to accommodate these motions. Some use a braided steel flex pipe between the exhaust manifold and converter, while others use a flexible spring-loaded connection at the head pipe or converter.

The Y-pipe on a V6 or V8 engine routes the exhaust from both sides of the engine into a common pipe that connects to the catalytic converter. Y-pipes are not used on V6 and V8 engines with dual exhausts.

2. To reduce cold-start emissions, some late-model vehicles have a small pre-catalyst or “pup” converter mounted inside or just behind the exhaust manifold(s). The pre-cat works the same as the main converter, but heats up and reaches operating temperature much more quickly. This also helps light off the main converter sooner, too.

3. Exhaust systems often have more than one muffler. A secondary muffler, called a resonator, may be located ahead or behind the main muffler to further attenuate noise in the exhaust. The resonator is usually smaller and less restrictive than the main muffler.

4. A cat-back system includes all of the exhaust components aft of the converter, such as the intermediate or crossover pipe, muffler, resonator (if used) and tailpipe. It would not include a head pipe or Y-pipe, as these are located ahead of the converter. Free-flowing aftermarket cat-back systems are often used to reduce backpressure and improve power and fuel economy.

When a muffler or resonator rusts out, the adjacent exhaust pipes often have to be replaced, too. Replacing pipes requires clamps for each end, or in some cases gaskets if the pipe connections have bolt-together flanges (which are used on some import applications). New gaskets would also be required if replacing a cracked exhaust manifold. New hangers and/or heat shields would be recommended if the original parts are in poor condition, broken or missing. Loose or cracked heat shields can cause rattles. Missing shield should be replaced to keep heat away from the floor of the vehicle, or near fuel or brake lines.

 

Sections covered:

Automatic Transmission

Batteries

Brakes

Cooling System

Drivetrain

Emissions

Engine Mechanical Parts

Exhaust

Fuel System

HVAC

Gaskets

Ignition System

Manual Transmission

Suspension and Steering

Management

 













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