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11 - 2
EXHAUST SYSTEM
DESCRIPTION AND OPERATION (Continued)
EXHAUST GAS RECIRCULATION (EGR)
To assist in the control of oxides of nitrogen (NOx)
in engine exhaust, all engines are equipped with an
exhaust gas recirculation system. The use of exhaust
gas to dilute incoming air/fuel mixtures lowers peak
flame temperatures during combustion, thus limiting
the formation of NOx.
Exhaust gases are taken from opening in the
exhaust manifold passage to the intake manifold.
Refer to Group 25, Emission Control Systems for a
complete Description, Diagnosis, and Service Proce-
dures on the exhaust gas recirculation system and
components.
HEAT SHIELDS
Heat shields (Fig. 2) are needed to protect both the
vehicle and the environment from the high tempera-
tures developed near the catalytic converters. All
engines are equipped with a heat shield crimped on
the top of the convertor.
Avoid application of rust prevention com-
pounds or undercoating materials to exhaust
system floor pan heat shields on cars so
equipped. Light over spray near the edges is
permitted. Application of coating will greatly
reduce the efficiency of the heat shields result-
ing in excessive floor pan temperatures and
objectionable fumes.
The combustion reaction caused by the catalyst
releases additional heat in the exhaust system. Caus-
ing temperature increases in the area of the catalytic
convertor under severe operating conditions. Such
conditions can exist when the engine misfires or oth-
erwise does not operate at peak efficiency. Do not
remove spark plug wires from plugs or by any other
means short out cylinders if exhaust system is
equipped with catalytic converter. Failure of the cat-
alytic converter can occur due to temperature
increases caused by unburned fuel passing through
the converter.
The use of the catalysts also involves some non-au-
tomotive problems. Unleaded gasoline must be used
to avoid poisoning the catalyst core. Do not allow
engine to operate at fast idle for extended periods
(over 5 minutes). This condition may result in exces-
sive exhaust system and floor pan temperatures.
EXHAUST SYSTEM GROUND STRAP
All vehicles are equipped with a ground strap on
the exhaust system. The ground strap is attached
from the rear muffler bracket to the body (Fig. 2).
The ground strap is used to suppress radio frequency
interference/static.
EXHAUST FLEX-JOINT COUPLING
A exhaust flex-joint coupling (Fig. 3) and (Fig. 4) is
used to secure the catalytic converter to the engine
manifold. This joint actually moves back and forth as
the engine moves, preventing breakage that could
occur from the back-and-forth motion of a transverse
mounted engine.
The exhaust flex-joint is welded to the catalytic
converter.
Fig. 2 Heat Shields
JA
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