Codep0300 05 xterra replaced plugs and still have miss fire whats next diagnosis?

Question

Car ran fine one day next day start up the car engine light started flashing I know I already had a burnt cat code P0420 that's been there since the day i owned it but then on this day the engine started misfiring engine light flashing code p 0 300 so I did an oil change and replaced the spark plugs but still have same code what's next? I know the spark plugs on the driver side wear white tip the passenger side they were all black any clue why?

Answer 1

P0420 is catalytic convertor on Bank 1, you have 2 catalytic convertor Bank 1 and Bank 2, if the sparkplug are black on the other side you can be partial plug on Bank 2, what you can do to troubleshoot Bank 2 is loosens the exhaust flange on Bank 2, (you may set a 02 code on bank 2 and a catalytic code Bank 2) note any performance difference, if the misfire is relived , bank 2 maybe partial plugged. You can go this route or use a exhaust back pressure. You can go that route or remove the upstream  02 sensor on Bank 2, If you go this route you have to reconnect the harness of the 02 sensor on Bank2 and secure away from any exhaust heat if you do not reconnect you can set a misfire code on Bank 2.