How did you know it was misfire? Did you use a code reader to get the info?
这个可能是火花塞的问题, 还是cable和点火线圈呢. It could be any of them or none (a temperary problem). Use a code reader (or take your car to a garage to do it for you) to find the exact problem, reset it to see if it happens again.
Ford and GM cars are extremely difficult for simple job like replacing the spark plugs as compare to the Jap cars. Especially replacing plugs at bank 1 near firewall. They want you to bring it back to the dealer. Not sure is this called smart design?