Chapter 18 Diagnosis and Repair of the Emission Control and Exhaust Systems 399
Copyright by Goodheart-Willcox Co., Inc.
Converter Installation
Before installing the new converter, install any acces-
sory equipment, such as the oxygen sensors. To install the
replacement converter, place it in position and attach all
mating pipes or fl anges. Then, install the pipe and hanger
fasteners. Ensure that the converter is properly aligned
with the rest of the exhaust system and the vehicle body,
Figure 18-41. Finally, tighten all of the fasteners.
Follow-up for Emissions and Exhaust
Repairs
After repairs, clear the ECM of any codes that may
have been set during the diagnostic procedure. However,
remember that if the vehicle must pass an emissions test,
do not erase any trouble codes. Doing so will remove any
monitors that are set. If necessary, conduct a drive cycle to
reset the monitors.
Road test the vehicle to ensure it performs normally
with no unusual noise or odor. Perform another exhaust gas
analysis to verify proper operation of the emission control
system. If your shop has the proper permits, perform an
air-quality reinspection if the vehicle was in for failing a
state air quality test. If the problem is not corrected, begin
the diagnostic procedure again.
Summary
Emissions tests are performed in various states to com-
ply with federal emissions laws. There are two main types
of state emissions tests: enhanced emissions tests and static
emissions tests. During an enhanced emissions test, the
vehicle is operated on a dynamometer as emissions levels
are measured. During a static emissions test, emissions are
measured as the engine idles. In many states, the vehicle’s
gas cap is also checked.
Various equipment is used to perform vehicle emis-
sions tests. Emissions test procedures vary greatly between
states and sometimes between different areas of the same
state. Consult your local emissions inspections authority for
exact procedures.
Most problems in the emission control system will only
show up when the vehicle fails an emissions test. In many
cases, the emission-control devices are not the source of
the problem, but are overwhelmed as the result of other
engine problems. If the vehicle fails an emissions test, it
must be adjusted or repaired to bring it up to the proper
specifi cations.
Before diagnosing emission problems, determine that
the exhaust system has no obvious problems, including
defective components and signs of tampering. Check for
exhaust restrictions if necessary. A drive cycle can be per-
formed as necessary.
If a vehicle is brought in for repairs after failing a state
inspection, it should be retested before proceeding. Make
sure the readings obtained by the shop exhaust gas ana-
lyzer approximately match the readings of the state emis-
sions test.
The PCV system can be checked by visual observa-
tion. The evaporative emission control system can be
checked for fl ow restrictions, vacuum buildup, and leaks.
Plugged fi lters in the charcoal canister or restricted hoses
cause many problems in the evaporative emission control
system. A smoke machine may be required to locate leaks
in the evaporative emissions control system.
EGR valves can become clogged with deposits, usu-
ally on high-mileage vehicles. Defects with the vacuum
supply are the most common cause of EGR problems.
Electronic EGR valves can have an electrical fault or may
have a defect in the wiring. On an ECM-controlled EGR
system, be sure not to damage the ECM drivers while mak-
ing electrical checks.
The air pump should be checked for proper output. If
there is no output, check the condition and tension of pump
drive belt before replacing the pump. Most other problems
with the air pump system are caused by valve defects.
Thermostatic air cleaners can be checked for proper
closing when cold and full opening when hot. Also check
the EFE system to ensure that the valve closes when cold
and opens when hot. Checks to both of these systems can
be made with a vacuum pump. A scan tool can be used to
help with diagnosis on some systems.
Some PCV systems and charcoal canisters have fi lters.
These fi lters should be checked often and replaced (if
replaceable) when they show any signs of plugging.
If an exhaust system restriction is suspected, the system
may need to be disassembled to check it. Common sources
of restrictions are stuck EFE valves, clogged converters or
muffl ers, kinked pipes, or double-wall pipes in which the
inner pipe has collapsed.
Figure 18-41. The catalytic converter is replaced as a separate component of the exhaust system. In some cases, a section of pipe,
such as a Y-pipe is replaced with the converter.
Muffler
Muffler
Converter
Engine Engine
Replace
Replace
Converter
Converter