Town Car V8-4.6L (2008)
Typical Bank 1 Catalyst 3 HO2S Configuration
The purpose of the exhaust system is to convey engine emissions from the exhaust manifold to the atmosphere. Engine exhaust emissions are directed
from the engine exhaust manifold to the catalytic converter through the front exhaust pipe. A HO2S is mounted on the front exhaust pipe before the
catalyst. The catalytic converter reduces the concentration of CO, unburned HCs, and NOx in the exhaust emissions to an acceptable level. The
reduced exhaust emissions are directed from the catalytic converter past another HO2S mounted in the rear exhaust pipe and then on into the muffler.
Finally, the exhaust emissions are directed to the atmosphere through an exhaust tailpipe.
On some PZEV, there is a total of 3 HO2S in the exhaust stream. One near the exhaust manifold (stream 1), one in the middle of the light-off catalyst
(stream 2), and the third (stream 3) is mounted after the light-off catalyst.
Underbody Catalyst
The underbody catalyst is located after the light off catalyst. The underbody catalyst may be in line with the light off catalyst, or the underbody
catalyst may be common to 2 light off catalysts, forming a Y pipe configuration. For an exact configuration of the catalyst and exhaust system for a
specific vehicle, refer to Exhaust System for the exhaust system-exploded view.
Three-Way Catalytic (TWC) Converter
The TWC converter contains either platinum (Pt) and rhodium (Rh) or palladium (Pd) and rhodium (Rh). The TWC converter catalyzes the oxidation
reactions of unburned HCs and CO and the reduction reaction of NOx. The 3-way conversion can be best accomplished by always operating the
engine air fuel/ratio at or close to stoichiometry.
Exhaust Manifold Runners
The exhaust manifold runners collect exhaust gases from engine cylinders. The number of exhaust manifolds and exhaust manifold runners depends on
the engine configuration and number of cylinders.
Exhaust Pipes
Exhaust pipes are usually treated during manufacturing with an anti-corrosive coating agent to increase the life of the product. The pipes serve as
guides for the flow of exhaust gases from the engine exhaust manifold through the catalytic converter and the muffler.
Heated Oxygen Sensor (HO2S)
The HO2Ss provide the PCM with information related to the oxygen content of the exhaust gas.
Muffler
Mufflers are usually treated during manufacturing with an anti-corrosive coating agent to increase the life of the product. The muffler reduces the level
of noise produced by the engine, and also reduces the noise produced by exhaust gases as they travel from the catalytic converter to the atmosphere.
