Troubleshooting misfire, How concerned should I be about this?

[jadez03]

Troubleshooting a misfire in my 4.6L 3V V8. Ran rough this morning, pulled codes after work...misfire on 7. Replaced 7. First pic is old plug on right and brand new plug on left. Second pic is the same but the new plug after 1mi of test driving where the misfire returned. How concerned should I be about the rusty spots from the spark end? I thought maybe boots are bad, but the boots hook on the other end. (Swapped boots 6 and 7 just in case) Thanks for any tips.

 

[Bazz270]

What brand this plugs are?

Begin from replacing to oem/motorcraft plug and a coil on the bad cylinder ,then check the coil harness.

 

[66427]

Troubleshooting a misfire in my 4.6L 3V V8. Ran rough this morning, pulled codes after work...misfire on 7. Replaced 7. First pic is old plug on right and brand new plug on left. Second pic is the same but the new plug after 1mi of test driving where the misfire returned. How concerned should I be about the rusty spots from the spark end? I thought maybe boots are bad, but the boots hook on the other end. (Swapped boots 6 and 7 just in case) Thanks for any tips.

View attachment 434410

I know you said 7...

 

[1.8TTony]

Swap #7 coil with another and see if the misfire follows that coil. If it does, replace the coil. If it doesn't, check #7 ignition coil wires for damage. If that doesn't solve the problem, do the same with with #7 fuel injector.