Yes I know there are 10,000 threads on this topic but I need a little more help. I had COP 2 & 3 as well as Plugs 2 & 3 replaced 6 1/2 months ago (14,000 miles ago) while I was on vacation. The other day my truck started throwing codes for misfire cylinder 3, system too lean, and misfire on start up. I pulled COP 3 out last night and cleaned it off but I swapped it with COP 1 to see if it would through a new code - it did not. Unfortunately I broke the COP connector on top while connecting COP 3 back up. I put the code reader back onto my truck and it only shows a code for the broken connector on cylinder 3... should I be worried that Plug 3 or the original COP 3 is going bad or could just cleaning it off really take care of my issues? I am going tonight to pick up a new connector and replace it to see if my truck keeps misfiring and idling rough or not.

 

bump

 

I would test the cop with a multi tester to see if it's good and then go from there

 

what type plugs and COP did you use 6 months ago ? and if you swapped the COP from 3 to 1 and made no difference than... I would say its the plug..

 

The only way to test COPs is to put them under load, which you can't do on a bench. Did you use Motorcraft COPs or another brand? I would replace it with a MC one and see if that fixes the problem

 

Primary and secondary resistance could be done on a bench. If they are within spec then chances are it is good...not full proof but it's a start

 

Ford installed Motorcraft plugs and COPS.... they had a 12 month/12,000 mile warranty on them. Of course I put 14,000 miles on since then lol. I ended up not being able to get the COP connector pigtail last night so that'll be on the list for tonight. I'm hoping it'll fix everything. I just want my truck running right again..

 

Ended up being plug 3 being bad and plug 4 wasn't even tightened down in the head... It was just sitting in there. The truck runs better than it ever has now!