Tech Stuff

Catalytic converter diagnosis


Editor’s note: Thanks to Charles Pantano and Jack George of Eastern Catalytic for their assistance in providing this information to our readers.

All art courtesy Eastern Catalytic

It is not uncommon for technicians to misdiagnose a driveability or emissions issue by blaming the converter. In many cases, it’s not the converter’s fault, but rather one of the engine components upstream from the catalyst. Yes, a converter can fail, but more often than not, the root cause might involve upstream components such as an 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 2,000 degrees Fahrenheit, 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.

Engine running too hot.
<p>Engine running too hot.</p>

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 degrees F, so when exposed to exhaust temperatures of 1,200 degrees F, 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.

Engine oil entering exhaust.
<p>Engine oil entering exhaust.</p>

Impact under vehicle crushing converter.
<p>Impact under vehicle crushing converter.</p>
Tags: Fuel trim 
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