There is a stunning statistic that was related to me at a recent Emissions Tech 2009 update class. Nationwide, over 60% of all the Catalytic Converters replaced in order for a vehicle to pass an emissions test are failing less than six months later--in fact, the catalytic converters are failing so severely that six months later, the new CAT and vehicle will again fail the emissions test. This means that the vehicle is back to inefficient performance and wasting fuel, based on what is being released from the tailpipe. How could a perfectly good CAT go bad so fast?
The answer is that the 'root cause' of the emissions problem was never addressed. The Catalytic Converter was replaced to 'mask' the real problem. When a vehicle is new, it barely needs a CAT in order to run 'clean' other than during warm-up or when it is under a heavy load. As the engine management components, i.e., the spark plugs, wires, coil(s), air and fuel filter, injectors, oxygen sensor(s), EGR system wear and get dirty with carbon, the performance efficiency of the engine degrades drastically. This why the 'Check Engine Light' was created. It's a signal that the engine is running poorly and one or more systems have reached their maximum level of compensation or have even failed.
The point is, be sure to have the root cause of WHY the Catalytic Converter failed, thoroughly inspected, and then completely repaired and/or serviced. After this is done, the vehicle should 'squeak by' or just barely fail an emissions test. Then a CAT replacement is appropriate. If the engine is still running 'dirty' and the CAT has to clean up more than 10-20% of the emissions, the car has not been accurately diagnosed and repaired.
(Next post: Are OEM (factory quality parts) important or even necessary?)