i have a 97 f-150 i notice it had a miss had it checked and had a faulty plug which damaged the piston on #4 so i had the engine replaced had the codes reset and still had a miss fire on #4 i changed the plugs, wires,and coils then worked my way to the injecters everything checked out fine. now it has a miss on #3 #4 #7 can this be a problem with the pcm? i am truly stumped .