Ford BR3Z-5E212-C Catalytic Converter Assembly

The amount of oxygen is critical because the catalyst cannot convert harmful pollutants into harmless compounds without it. The catalyst is most efficient at capturing and storing oxygen when the exhaust gases are mixed at the ideal (stoichiometric) air/fuel ratio of 14.7:1. If the air/fuel ratio is too lean or too rich for an extended period, it can affect the catalyst's ability to function properly.