Will a bad catalyst cause random multiple misfire?

Question

I had codes p0300 (random misfire), p0301, p0303 and p0305. Also p0340 (cmp sensor). Also p0420 and p0430 (catalyst below efficiency bank 1 and 2). Replaced ignition coil packs and spark plugs. Replaced both cmp sensors. Noticed oil in cylinder 3 and 5 coil wells so I replaced valve cover gaskets and tube seals. No check engine light on, car runs great at low speeds, but when accelerating over 55 on highway loses power, sputters, bucks and knocks like its missing on 1 or more cylinders. Check engine light comes on flashing. Codes p0301, 303 and 305 come back. My thought is: Random misfire caused unburnt fuel in exhaust to ruin catalyst so it needs replaced. My question is: will replacing it stop the misfire? 2006 Hyundai sonata 3.3L v6 Lambda

Answer 1

P0300 Random misfire

P0301 Misfire number 1 cylinder, P0303 Misfire number 3 cylinder, P0305 Misfire nuber 5 cylinder

The catalytic can get damage by prolong misfire that it may need to be replaced. If it got so bad that it plugged the exhaust system you would have random misfire but you would not be able to get to 55 on highway.and you would hear a muffling noise in the airfilter area. The misfire you have is all on one side of the Bank .A plugged catalytic will not cause just one side of the bank to misfire. it effects both bank . What a plugged catalytic will do is will decrease the spark voltage burn time and burn voltage where the engine suffercates so both side of the bank are affected and you will get Random misfire. If you can take coil 3 and 5 and place it in 2 and 4 see if the misfire moves.You may just have 2 failing coils.