I changed my spark plugs and noticed it was smoking really badly during the process of changing them there was oil on top of the spark plugs so I drove it to the driveway and change my valve cover gaskets put everything back together started it up and it backfired took me awhile to figure out it's coming from the number four cylinder I replaced the spark plug again and the coil pack it's still backfires and throws po300 code if I unplug the number for coil pack no more backfire but it's obviously running off five cylinders I need help