Rep Power: 0

i have a 2007 honda civic ex sedan 1.8L and received a P0420 code about almost a month ago. I looked this code up and it comes up as Catalyst efficiency below threshold.. slowly but surely as the weeks grew on i noticed my engine becoming louder day by day. This usually happens when its at its worst when i either just started the car or accelerating. It sounds like a single engine prop plane at full throttle when im accelerating, its pretty rough... There is also a slight smell but i cant pin point what smell it could be, but it does remind me of a day out with like a hundred dirt bikes.. that kind of like gas and engine smell type thing.. lol i just want to know what to do to fix this and what u think the underlying problem or object that is causing...please help thank u

 
Rep Power: 222

sounds like you need to get your exhaust checked out