Nissan Repair: check engine light, internal combustion engine, bosch platinum

Question
I have a 2001 Frontier 4cyl 2WD reg cab 123,000 miles check engine light is on, I get a P0420 code,the generic reading on the Actron Reader says "Catalyst efficiency below threshold, bank one. The factory service manual says possibles are, spark plugs, timing, injectors, catalytic converter.Before the light came on, I changed both oxygen sensors.(I used Bosch) Also per your suggestion when the light came on about 1000 miles ago, I changed the plugs from the Bosch Platinum 4 to the OEM Nissan/NGK. I found a large pin hole in the front of the muffler below where the pipe fits in. Could this cause the light to go on and give me the P0420 reading?  

Answer
Rich,

You probably have sticky injectors and that is causing a over rich condition.  I would add some Berrymans Chemtool fuel injector cleaner to the gas and see if that does the trick.  If not, then you are looking at ohms checking all the injectors to the factory specs and any that fall out of range should be replaced.

The hold in the muffler is for water to escape.  Interestingly enough, for every gallon of gas burned by the internal combustion engine about four gallons of water are produced.  So, when the vapor turns back into a liquid it has to get out or it will rot the exhaust...