GM Blazer/Jimmy/Typhoon/Bravada 1983-1993 Repair Guide

Catalytic Converter


All gasoline engine vehicles covered by this guide are equipped with a catalytic converter in order to reduce tail pipe emissions. Most of the vehicles are also equipped with an electronically controlled closed loop fuel system which makes possible the use of a three-way reduction type catalytic converter instead of only an oxidizing catalyst converter. Though both converters act in a similar fashion, the three-way unit reduces additional emissions which a single oxidizing converter cannot. A three-way converter is used to reduce HC, CO and NOx in the engine's exhaust. The actual catalyst contains Platinum (Pt) and Rhodium (Rh). A few grams of catalyst are applied evenly onto a ceramic honeycomb, which is then installed into a stainless-steel enclosure. The unit is mounted in the exhaust system close to the engine for rapid warm-up to operating temperature.

The function of the catalytic converter is to reduce CO, HC, and NOx by causing these gasses to easily combine with oxygen forming mostly CO 2 , N 2 and water. A very precise amount of exhaust gas oxygen is required for the three-way catalyst to function properly. On these vehicles a computer module (ECM, PCM or VCM) reads the oxygen sensor signal and then controls the carburetor mixture solenoid or fuel injector(s) so there is almost always the exact amount of oxygen required for proper catalyst operation.

A catalytic converter operates at temperatures up to 1500°F (815°C). It can be damaged by prolonged idling, a rich air/fuel ratio or by a constant misfire. Excess fuel will cause the unit to overheat and melt the ceramic substrate. Use of leaded fuel will quickly poison the catalyst and should be avoided. On vehicles sold in the US, catalytic converters are covered by factory warranty for at least 50,000 miles. However with proper care, on most vehicles a catalytic converter should still be effective for more than 100,000 miles.

  1. Keep the engine in proper running condition at all times.
  3. Use only unleaded fuel.
  5. Avoid prolonged idling. Proper air flow past the catalytic converter is required to prevent overheating.
  7. Do not disconnect any of the spark plug wires while the engine is running.
  9. Make engine compression checks as quickly as possible to minimize the fuel pumped into the exhaust system.

If replacement of the catalytic converter or exhaust pipe components is necessary, refer to Engine & Engine Overhaul of this guide for the relevant procedures.