I have a misfire on cylinder 4 again. This happened about 6 months ago so I changed the spark plugs and wires. This did not help, but they probably needed to be changed anyway. Then, I used Lucas fuel treatment and after the second bottle, things cleared up and I was okay. Just last week, it happened again. Although, after the second treatment of Lucas, the problem is still there. Would the next thing to do is change the fuel injector? The other engine code is system too lean. Just wondering what the next step would be.