I own a 2002 3.8l Camaro and have installed a flowmaster exhaust system (cat-back) and a K&N Intake. Recently i have been having a lot of problems with my car putting up a P0420 code which is something like Catalyst Threshold Effiency Low (Bank 1). My shop installed a new catalytic convertor on my car...and just a few weeks later the code came back on again. The shop owner seems to think that my air intake is putting to much air into the engine and its running lean. I had the intake on for motnhs before i started having these problems. Does anyone have any suggestions that may be causing my engine to be running lean? By the way...ive also replaced the plug wires and fuel pump already this year. This is getting expensive and fast already.

 

Low efficiecy means the cat is not cleaning the air. Could be due to a misfire or bad O2 sensor on bank 1, either upstream or downstream. Check the sensors for proper activity using a scanner. The car has a MAF sensors, so it can easily compensate for minor mods, such as a CIA.

 

i had a similar problem, my temp sensor was bad and it was pretty much saying the car was cool and dumping fuel into it, so it would run really rich, and eventually flood, and then gas got built up in my cats and caused it to through a code too

 

So what was the fix? Obviously the air filter is the first thing to check/change/clean...

 

I would say O2s would be a good place to start. But as said above your intake air temp sensor could also cause some issue's.