Look upstream for the culprit in a converter failure

“Posted with permission from Motor Age magazine”

By: Charles Pantano, Eastern Catalytic

Catalytic converter technology has come a long way in meeting the demands of modern engines to deliver the required emissions efficiency and long-term reliability. Yet, in spite of these advances, converters still fail, ultimately igniting the CEL (Check Engine Light) and potential warranty claims. In many cases, it’s not the converter’s fault, but rather one of the engine components upstream from the catalyst.

Keep this in mind when you are troubleshooting converter issues and you’ll stand a good chance of solving the problem faster and preventing it from reoccurring. You’ll also avoid troublesome and unnecessary warranty hassles.

There are several engine components that play a major role in catalytic converter efficiency and can also contribute to its demise. They include: O2 sensor, fuel injectors, spark plugs, EGR valve system, exhausts manifolds, vacuum hoses, and MAF sensors.

Thermal Failures: Although modern three way converters (TWC) can withstand short exposures to 2000 ºF, engine exhaust conditions caused by failed or out of tolerance parts can push temperatures above the converter’s operating limit. Excessive rich fuel conditions and exhaust leaks ahead of the converter are prime examples. They result in higher than normal temperatures that can cause matting erosion and burn away or melt converter coatings. If temperatures are high enough, the ceramic substrate itself will melt and clog.

Contamination: If silicone products are used to seal any part of the exhaust system including the exhaust manifold and gaskets, O2 sensors, and exhaust tubing, you’ve got problems. At best, the highest rated silicone can only handle 700 ºF, so when exposed to exhaust temperatures of 1200 ºF, it quickly burns and outgases, leaving a silicone coating on the O2 sensor or converter wash coating. The results include engine conditions that are out of operating range and reduced efficiencies within the catalytic converter.

Coated or Fouled: Anything that gets through the combustion chamber and reaches the face of the converter can reduce catalyst efficiency. Liquids such as antifreeze from leaking manifolds and oil from head gasket failures top the list of troublemakers.

Engines in need of service and older engines that burn oil due to worn cylinder walls, stuck rings, and worn valve guides will produce by-products that can foul the converter.

Common causes of converter failure

Here are some illustrations of converter failures that should make you look elsewhere in the engine for the real cause of the problem. Failures caused by these problems are not covered by the manufacturer’s warranty.

Charles Pantano is the Certification Program Manager at Eastern Catalytic a leading innovator and world-class manufacturer of catalytic converters, offering a full range of universal, direct-fit, manifold, diesel, and heavy-duty catalytic converters.