GM Metro/Sprint 1985-1993 Repair Guide

Catalytic Converter

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OPERATION



This system reduces Oxides of Nitrogen (NOx) and oxidizes Hydrocarbons (HC) and Carbon Monoxide (CO). In order for the converter to function properly the air/fuel ratio of the fuel system must be constantly maintained 14.7:1.

SERVICE



Check to be sure a light can be seen through the catalytic converter when removed. If not, replace the converter. This unit is usually covered under the 5/50 emissions warranty.

  1. Carefully remove the oxygen sensor. Install an exhaust back pressure tester or equivalent, in place of the oxygen sensor.
  2.  
  3. With the engine at normal operating temperature, observe the tester reading on the gauge. The reading should not exceed 1 / 4 psi (18.6 kPa).
  4.  
  5. Accelerate the engine to 2000 rpm and observe the gauge. The reading should not exceed 3 psi (20.7 kPa).
  6.  
  7. If the back pressure at either rpm exceeds specifications, an exhaust system restriction is indicated.
  8.  
  9. Inspect the entire system for a collapsed pipe, heat distress or internal muffler failure. If there are no obvious reasons for excessive back pressure, a restricted catalytic converter should be suspected.
  10.  

REMOVAL & INSTALLATION



The catalytic converter is an integral part of the front exhaust pipe assembly. If the converter requires replacement, the front pipe assembly must be replaced as a unit.

  1. Raise and support the vehicle safely.
  2.  
  3. Remove two bolts and disconnect the front pipe/catalytic converter assembly from the exhaust manifold.
  4.  
  5. Remove two nuts and disconnect the front pipe/catalytic converter assembly from the resonator/muffler/tailpipe assembly.
  6.  
  7. Remove the hanger supporting the catalytic converter and remove the front pipe/catalytic converter assembly from the vehicle.
  8.  

To install:
  1. Clean the gasket mating surfaces thoroughly.
  2.  
  3. Install the front pipe/catalytic converter assembly to the vehicle and support catalytic converter with hanger.
  4.  
  5. Connect the front pipe/catalytic converter assembly with a new gasket to the resonator/muffler/tailpipe assembly. Secure with two nuts by do not tighten fully.
  6.  
  7. Connect the front pipe/catalytic converter assembly with a new gasket to the exhaust manifold. Secure with two bolts by do not tighten fully.
  8.  
  9. Align all system components properly to prevent any noise or vibrations before tightening fasteners.
  10.  
  11. Tighten resonator/muffler/tailpipe assembly nuts to 26 ft. lbs. (35 Nm) and front pipe/catalytic converter assembly bolts to 37 ft. lbs. (50 Nm). Tighten catalytic converter hanger bolts to 11 ft. lbs. (15 Nm).
  12.  
  13. Lower vehicle. Start the engine and check for leaks.
  14.  

 
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