What causes po 457 I replaced cap with after market one and cvs and code came bck after 1 week

Question

Light is coming on po 457 did a smoke test and it comes out around new cvs and also on gas cap

Answer 1

here is the service bulletin from ford

 

http://www.stangnet.com/images/stories/docs/sn95_TSBs/03-20-03.pdf