Plugs or Coil Pack or O2 or combo?

[ManUpOrShutUp]

Any way to ensure a COP is good?

Yes. https://easyautodiagnostics.com/ford/4.6L-5.4L/how-to-test-the-cop-coils-1

 

[TobyU]

Sorry but that guy is applying too many other engine and car principles to the ford COP and saying they are rules when it just doesn't play out that way in real life on fords.
In the book and online are one thing BUT.

You do not need a spark tester. I disagree. An old plug works fine BUT. I don't put much faith in checking COPs this way anyway.

I am all about the cylinder balance test but I prefer to cancel out COPs not injectors but either way works but mine is better ...read on.
It is easy to spot a dead one but often they are intermittent.
Unplugging and plugging in COP is better because I have seen several that was dead miss after 2-3 good fires. Each time you plugged unplugged it...as soon as you plugged it back in it was smooth as silk for 2-3 seconds then solid miss.

I have never damaged a COP from using spark plug or allowing it to spark by pulling it up off of plug...but I see little reason to do this.
These are far more durable than that. They misfire and get wet and short out and do that for hours and weeks and still coils are good!

Any ohming out tests are a very basic test and can't be trusted in real use when hot and firing over and over etc.

Best way is code scanner and look at mode $6 results for misfire counts on repeated scans after clearing codes each time.

Then go to suspected ones from results and unhook connectors and reconnect seeing if you get short amount of no missing but too often it is not missing when you are testing it.

Back to mode 6 and swap a couple to different locations to see it if moves.

Also, if you have done it recently, you should always pull coils up and blow strong compressed air into plug wells to get moisture/coolant, leaves, sticks, twigs and dirt out of there.

 

[rjdelp7]

Driving with that misfire, caused catalytic converter damage. That is why your getting Cat below threshold.

 

[TobyU]

Driving with that misfire, caused catalytic converter damage. That is why your getting Cat below threshold.

Exactly. I have bought several vehicles that would pop the code because they have been driven with a misfire. If it's not too bad it hasn't melted and plugged the converter you don't have to replace it. And usually you don't. I have had good luck running three to four bottles of 91% isopropyl alcohol and with the gas down below a quarter of a tank. This seems to clean the converter and make the code stay away longer.