Answer: The vehicle destroyed the converter due to engine malfunction. A converter that has a melted substrate has experienced temperatures in excess of 2000 degrees F (1200 C). A converter typically will not exceed 1000 degrees F (600 C) when installed on a properly operating vehicle. It is necessary to repair the engine malfunction before replacing the converter. Otherwise, the new converter will melt too. Common causes of melted converters include:
1. Three-way plus air vehicle running rich—when the air is injected in the converter, the rear brick melts because the excessive fuel now has enough oxygen to burn in the converter.
2. Vehicle running rich with exhaust pipe leak—air is drawn into the exhaust pipe, combines with the excessive fuel and burns in the converter.
3. Vehicle misfire—air/fuel charge leaves the combustion chamber without firing, travels through the exhaust pipe and burns in the converter.
"I put an new aftermarket converter on a vehicle that had failed for NOx on the state emission inspection test, but when the vehicle was retested it failed again. I finally put an O.E. converter on it and it passed. What's wrong with the aftermarket converter?"
Answer: There's nothing wrong with the aftermarket converter - it was simply installed on a vehicle with a severe NOx problem caused by one or more upstream mechanical issues. The O.E. unit passed the test, but had NOx levels that were still much higher than they should have been with a brand new OE converter installed. The reason that the OE converter performed better than the aftermarket converter is because the OE converter is designed to last 80,000 miles and the aftermarket converter is designed to last 25,000 miles. The extra durability is achieved with extra catalyst. When the converter is new, this extra catalyst increases the converter's efficiency, but also increases the cost of the OE unit. The root cause of the vehicle's NOx problem remains, however.
Standard aftermarket converters, by comparison, don't provide that extra margin of safety in the form of added catalyst. As a result, vehicles with upstream emissions issues, particularly related to NOx, deserve special care when diagnosing the vehicle because the most effective means of repair is to correct the problem that is generating the excessive NOx in the first place. In these cases, the most economical means of repair may be a combination of engine repair and the installation of a "Premium" aftermarket converter — such as the new Clean Air Ultra universal converter. A "Premium" aftermarket converter features increased catalyst similar to an OE converter, without the high cost of an OE part.