Dodge ZB 2005 Service Manual page 738

ZB
HEAT SHIELDS
DESCRIPTION
High temperatures can develop around the cata-
lytic converters and resonators. Because of this, heat
shields (Fig. 5) and (Fig. 6) are necessary to protect
both the car and the environment.
Fig. 5 Catalytic Converter Heat Shield (Right Side
Shown - Left Side Typical)
1 - RIGHT INNER FRAME RAIL
2 - STUD
3 - HEAT SHIELD
4 - NUT
CATALYTIC CONVERTER(S)
OPERATION
The three-way catalytic converter simultaneously
converts three exhaust emissions into harmless
gases. Specifically, HC and CO emissions are con-
verted into water (H2O) and carbon dioxide (CO2).
Oxides of Nitrogen (NOx) are converted into elemen-
tal Nitrogen (N) and water. The three-way catalyst is
most efficient in converting HC, CO and NOx at the
stoichiometric air fuel ratio of 14.7:1.
The oxygen content in a catalyst is important for
efficient conversion of exhaust gases. When a high
oxygen content (lean) air/fuel ratio is present for an
extended period, oxygen content in a catalyst can
reach a maximum. When a rich air/fuel ratio is
present for an extended period, the oxygen content in
the catalyst can become totally depleted. When this
occurs, the catalyst fails to convert the gases. This is
known as catalyst punch through.
Proper catalyst operation is dependent on its abil-
ity to store and release the oxygen needed to com-
plete the emissions-reducing chemical reactions. As a
catalyst deteriorates, its ability to store oxygen is
reduced. Since the catalyst's ability to store oxygen is
somewhat related to proper operation, oxygen storage
can be an indicator of catalyst performance. Refer to
the appropriate powertrain diagnostic procedure for
diagnosis of a catalyst-related Diagnostic Trouble
Code (DTC).
The combustion reaction caused by the catalyst
releases additional heat in the exhaust system.
Under severe operating conditions, this causes tem-
perature increases in the area of the reactor. Severe
operating conditions can exist when the engine mis-
fires or otherwise does not operate at peak efficiency.
NOTE: If the exhaust system is equipped with a cat-
alytic converter, do not remove spark plug wires
from plugs, or short out cylinders by any other
means.
The catalytic converter can fail because of temper-
ature increases caused by unburned fuel passing
through the converter. This deterioration of the cata-
lyst core can result in excessively high emission lev-
els, noise complaints, and exhaust restrictions.
Unleaded gasoline must be used to avoid poisoning
the catalyst core. Do not operate the engine in neu-
tral above 1200 RPM for extended periods over 5
minutes. Because there is no air movement under
the vehicle, excessive exhaust system/floor pan tem-
peratures may result.
CAUTION: Due to exterior physical similarities of
some catalytic converters with pipe assemblies,
extreme care should be taken with replacement
parts. Internal converter differences are required in
some parts of the country (particularly vehicles
built for states with strict emission requirements).
REMOVAL
NOTE: This procedure covers removal of either the
right OR left catalytic converter. Remove the appro-
priate parts for the side that is being worked on.
(1) Raise vehicle on hoist (Refer to LUBRICATION
& MAINTENANCE/HOISTING - STANDARD PRO-
CEDURE).
(2) Remove sill panel (Refer to 23 - BODY/EXTE-
RIOR/SILL PANEL - REMOVAL) (Fig. 7).
EXHAUST SYSTEM 11 - 5