Safety glasses should be worn at all times when working on or near the exhaust system. Older exhaust systems will almost always be covered with loose rust particles which will shower you when disturbed. These particles are more than a nuisance and could injure your eye.
Whenever working on the exhaust system always keep the following in mind:
In addition to its pipes and hangers, the chief components of an exhaust system are the catalytic converter and muffler.
The converter contains 2 separate ceramic honeycombs coated with different catalytic material. The front catalyst is coated with a rhodium/platinum catalyst designed to control oxides of nitrogen (NOx), unburned hydrocarbons (HC) and carbon monoxide (CO). This is therefore called a three-way catalytic converter (TWC). The rear catalyst is coated with platinum/palladium and is called a conventional oxidation catalyst (COC).
The TWC converter operates on the exhaust gases as they arrive from the engine. As the gases flow from the TWC to the COC converter, they mix with the air in the secondary air system into the mixing chamber between the two ceramic honeycombs. This air is required for optimum operating conditions for the oxidation of the HC and CO on the COC converter. Air is diverted upstream of the TWC during cold start to provide faster catalyst light off and better HC/CO control.
The factory-installed exhaust system usually uses a one-piece muffler system. This means that the whole system, except for the converter and exhaust manifold, is welded into place. This in turn usually means that once the muffler goes, the whole system has to be replaced. The converter assembly is a bolt-on catalyst installed at the rear of the flex joint and between the inlet pipe and muffler.
Inspect inlet pipes, outlet pipes and mufflers for cracked joints, broken welds and corrosion damage that would result in a leaking exhaust system. It is normal for a certain amount of moisture and staining to be present around the muffler seams. The presence of soot, light surface rust or moisture does not indicate a faulty muffler. Inspect the clamps, brackets and insulators for cracks and stripped or badly corroded bolt threads. When flat joints are loosened and/or disconnected to replace a shield pipe or muffler, replace the bolts and flange nuts if there is reasonable doubt that its service life is limited.
The exhaust system, including heat shields, must be free of leaks, binding, grounding and excessive vibrations. These conditions are usually caused by loose or broken flange bolts, shields, brackets or pipes. If any of these conditions exist, check the exhaust system components and alignment. Align or replace as necessary. Brush shields are positioned on the underside of the catalytic converter and should be free from bends which would bring any part of the shield in contact with the catalytic converter or muffler. The shield should also be clear of any combustible material, such as dried grass or leaves.
The operating temperature of the exhaust system is very high. Never attempt to service any part of the system until it has cooled. Be especially careful when working around the catalytic converter. The temperature of the converter rises to a high level after only a few minutes of operation.