New plugs , new wires they used bosch double platinum plugs and a good wire set, since then I have changed out the plugs twice and am still getting a P0304 code which says it is #4 cylinder misfire, the only thing I haven't done is change out the injector, and I did get a code one time that was listed as an injector, that was several months ago , and now am wondering if the injector is starting to fail.