Ok so I let my girlfriend drive my car for an hour big mistake. She brought it back and the next time I drove it the CEL was on and the motor sounded louder than normal (only mod is k and n intake and borla catback). It was running very sluggish and felt like it was misfiring. I took it to my mechanic the next day and the code thrown was Catalytic efficiency. But also we had the diagnostic still hooked up and test drove it and misfiring on cylinder 1 and i think another one cant remember which. But my question is can a bad catalytic convertor cause this misfire?