Diagnosing Converter Issues
Converters don’t fail on their own; failure is usually a symptom of a larger problem. This is why it is important to identify the root cause of the failure and perform the repair prior to installing a new converter.
Most catalytic converter failures fall under one of three categories:
Overheated, melted or broken converters
Overheated, Melted or Broken Converters
Any malfunction causing an unusually high level of HC or CO (in conjunction with high levels of O2) to enter the converter, will dramatically elevate its temperature.
Potential causes for high HC readings may include:
Poor spark or no spark
AFR cylinder imbalance
Excessive engine or vehicle load
- Fuel delivery system or fuel quality
- Sluggish (worn out) O2 sensors
- Excessive backpressure
NOTE: Temperatures in excess of 1600°F may damage catalyst, without visible signs of melting.
Catalyst poisoning occurs when the converter is exposed to emissions containing substances that coat the working surfaces, enveloping the catalyst to the point it cannot contact - and treat - the exhaust.
Potential causes for coated or fouled substrate may include:
Excessive carbon buildup in exhaust
Internal coolant leaks (head/intake gasket)
Use of non-converter-safe gasket sealants
Excessive oil consumption (burning oil)
Improper fuels or additives (E85, diesel)
The primary cause of structural damage is road debris striking the converter. Normally, some evidence of impact is visible on the converter shield.
Other conditions that may potentially cause structural damage:
Metal fatigue/stress fractures
Stripped O2 sensor threads
Flex pipe failure
Air-gap pipe failure
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