misfire mil after new plugs and COPs, never once before

[dan diego]

I changed the COPs and spark plugs on my 2005 GT. Never had a misfire mil prior to the new components. So far, the 5 and 8 cylinder have had codes (p0355,p0358). I swapped those COPs (5 and 8) to other cylinders to see if problem followed COP. The next misfire was on 5 again so not the COP. I have to suspect the plugs. I bought and installed Motorcraft sp547. Anyone else have issue with these plugs?

 

[Bullitt95]

Did you use nickel antiseize? If so you may have accidentally contaminated the electrode.

 

[McFly2]

You might consider swapping injectors around to see if problem follows.