misfire mil after new plugs and COPs, never once before

dan diego

Member
Jul 31, 2018
7
1
13
52
San 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?
 
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