Mazda Trucks 1972-1986 Repair Guide

Catalytic Converter

Print

The 1976 and later trucks sold in California and almost all 1979 and later trucks have a catalytic converter installed in the exhaust system to aid in the reduction of HC and CO emissions. The only exceptions are some 1979-80 models sold in Canada.

The catalytic converter is a muffler-shaped device located between the exhaust manifold and the muffler. It is filled with beads containing platinum and palladium which, through catalytic action, enables the HC and CO gases to be converted into water vapor (H 2 O) and carbon dioxide (CO 2 ). The converter has a warning system (1976 only), consisting of a thermo sensor inserted into the side of the converter, which monitors temperatures, and a warming light on the instrument panel which lights when the sensor detects converter temperatures exceeding 1,742ºF (950ºC). The converter should be inspected periodically for cracks, corrosion, and any signs of external burning, and replaced as required.

WARNING SYSTEM TEST 1976 Vehicles



  1. Turn the ignition switch ON. The warning light on the instrument panel should light. Start the engine. The warning light should go off.
  2.  
  3. If the light does not light, check the bulb. If burned out, replace and retest the system.
  4.  
  5. If the light does not go out after the engine has started, shut off the engine and tilt the seatback forward.
  6.  
  7. Disconnect the thermo sensor wire electrical connectors.
  8.  
  9. Using an ohmmeter, check the thermo sensor circuit for continuity, on the sensor side of the wiring. If there is no continuity, replace the sensor. Reconnect the wires and repeat the test.
  10.  

REMOVAL & INSTALLATION



  1. Raise the truck and support it on safety stands.
  2.  


CAUTION
Be very careful when working on or near the converter. External temperatures can reach 1,500ºF (815ºC) and more, causing severe burns. Removal or installation should only be performed on a cold exhaust system.

  1. Loosen the nut and remove the thermo sensor from the side of the converter (1976 models).
  2.  
  3. Remove the front and rear flange attaching nuts.
  4.  
  5. Remove the nut and rubber support which secures the converter bracket, and remove the converter.
  6.  
  7. Installation is the reverse of removal.
  8.