Exhaust System: Description and Operation

THREE-WAY CATALYTIC CONVERTER





The three way catalytic converter is an emission control device added to the exhaust system to reduce pollutants in the exhaust gas stream and requires the use of unleaded fuel only.
The three way catalytic converter coating contains platinum and rhodium which lowers the levels of oxides of Nitrogen (N0x) as well as Hydrocarbons (HC) and Carbon Monoxide (CO).
Periodic maintenance of the exhaust system is not required. If the vehicle is raised for other service, it is advisable to check the condition of the complete exhaust system.

EXHAUST MANIFOLD/OXYGEN (02) SENSOR
The exhaust manifolds are cast iron. The oxygen sensor is located in the exhaust manifold of all engines.

EXHAUST MANIFOLD PIPE





The front exhaust pipe incorporates a stainless steel braided sleeve over a flexible bellows section along with the catalytic converter. The entire pipe assembly is welded joint construction and is only serviced as an assembly.

REAR HEATED OXYGEN SENSOR (H02S-2)





The heated rear oxygen sensor, mounted behind the catalytic converter, monitors oxygen content in the exhaust to determine the efficiency of the catalytic converter. The HO2S-2 is a four wire sensor; two of the wires heat the sensor (B+ and ground) and the other two wires are the signal reference and ground. The sensor acts as an electro chemical cell, or battery, to produce a voltage in response to the oxygen content in the exhaust. A bias voltage (voltage sent from the PCM) is between 350 mV and 550 mV which is the voltage the PCM will see when the sensor is inactive or cold. As the heater and the converter heat the sensor up to around 275 degrees C (527 degrees F), the sensor will produce its own voltage to counteract this bias voltage. Low voltage from the sensor indicates high oxygen content (lean mixture) whereas high voltage indicates low oxygen content (rich mixture). The wires to the sensor carry air reference, which is used to compare differences in oxygen from the atmosphere to the exhaust stream.
The rear HO2S-2 will react slower than the front OS2 due to the oxygen storage in the catalytic convener. The rear oxygen sensor is used only for convener efficiency, not for A/F ratio control.
The rear oxygen sensor operates between 275 degrees C (527 degrees F) to 850 degrees C (1562 degrees F).

EXHAUST/RESONATOR PIPE
The exhaust/resonator pipe is part the production exhaust system and is serviced by a "Service Only" assembly.

MUFFLER
The muffler is part of the production exhaust system and is serviced by a "Service Only" assembly.

HANGERS AND ISOLATORS
The exhaust system is supported by free hanging nabber mountings, which permit some movement of the exhaust system but do not permit the transfer of noise and vibration into the passenger compartment.
The installation of exhaust system supports/isolators is very important as improperly installed supports/isolators can cause annoying vibrations, which can he difficult to diagnose.

CLAMPS
Clamps are used for connecting exhaust system slip joints:
^ Saddle/U-bolt

SHIELDS
The heat shields are aluminum; they prevent exhaust system heat from penetrating the floor of the vehicle or the fuel tank. Inspect the shields for cracks, and tears. Shields must always be re-installed if they are removed for exhaust system or body repairs.