Catalytic converters
Note: Because of a Federally-mandated extended warranty which covers emission-related components such as the catalytic converter, check with a dealer service department before replacing the converter at your own expense.
Description
1. A catalytic converter (or catalyst) is an emission control device in the exhaust system that reduces certain pollutants in the exhaust gas stream. There are two types of converters. An oxidation catalyst reduces hydrocarbons (HC) and carbon monoxide (CO). A reduction catalyst reduces oxides of nitrogen (NOx). Catalysts that can reduce all three pollutants are known as «three-way catalysts.» The vehicles covered in this manual are equipped with two three-way catalysts.
Check
2. The test equipment for a catalytic converter (a loaded-mode dynamometer and a five-gas analyzer) is expensive. If you suspect that the converter on your vehicle is malfunctioning, take it to a dealer or authorized emission inspection facility for diagnosis and repair.
3. Whenever you raise the vehicle to service underbody components, inspect the converter for leaks, corrosion, dents and other damage. Carefully inspect the welds and/ or flange bolts and nuts that attach the front and rear ends of the converter to the exhaust system. If you note any damage, replace the converter.
4. Although catalytic converters don’t break too often, they can become plugged up. The easiest way to check for a restricted converter is to use a vacuum gauge to diagnose the effect of a blocked exhaust on intake vacuum.
a) Connect a vacuum gauge to an intake manifold vacuum source (see V6 engine).
b) Warm the engine to operating temperature, place the transmission in Park (automatic models) or Neutral (manual models) and apply the parking brake.
c) Note the vacuum reading at idle and write it down.
d) Quickly open the throttle to near its wide-open position, then quickly get off the throttle and allow it to close. Note the vacuum reading and write it down.
e) Do this test three more times, recording your measurement after each test.
f) If your fourth reading is more than one in-Hg lower than the reading that you noted at idle, the exhaust system might be restricted (the catalytic converter could be plugged, OR an exhaust pipe or muffler could be restricted).
Replacement
Note: The catalytic converters are integral components of the front exhaust pipe assembly, which connects the exhaust manifolds to the rest of the exhaust pipe assembly. Both catalysts are welded into the front exhaust pipe assembly, which is a one-piece assembly.
5. Raise the vehicle and place it securely on jack stands.
6. Disconnect the electrical connectors for the upstream and downstream oxygen sensors and remove all four sensors (see Oxygen sensors — general information and replacement).
7. Remove the three nuts at each of the upper flanges (see illustrations) that secure the front exhaust pipe assembly to the exhaust manifold flanges.
15.7a To detach the upper left end of the front exhaust pipe assembly from the left exhaust manifold, remove these nuts
15.7b To detach the upper right end of the front exhaust pipe assembly from the right exhaust manifold, remove these nuts
8. Remove the clamp (see illustration) that secures the rear of the front exhaust pipe assembly to the rest of the exhaust system and remove the front exhaust pipe assembly.
15.8 To detach the rear end of the front exhaust pipe assembly from the rest of the exhaust system, remove this clamp
9. Remove and discard the old flange gaskets from the mounting flanges. Be sure to use new gaskets at both mounting flanges. Also use new fasteners at both flanges.
10. Coat the threads of the nuts and bolts with anti-seize compound to facilitate future removal. Tighten the nuts that secure the front exhaust pipe assembly to the exhaust manifold and to the rest of the exhaust system securely. Installation is otherwise the reverse of removal