Had a misfire in cylinder 8 and so I changed plugs and wires, I used autolite copper plugs and duralast wires. I notice I had carbon build up in cylinder 3 and 4 when I changed the plugs. After I finished we cleared the check engine started it up and still notice a slight misfire, went back and checked all the plugs, plug gaps, and wires. Started it back up and still got the same thing, drove it around the block to see if I could get a check engine light to come on and it did it was a cylinder 3 and 4 misfire. Now I was wondering could it be the autolite coppers or something else. I have also checked injecters.