My truck is not showing a code so i'm having to go thru a process of elimination that isn't working out for me.
My symptom is a mis-fire that happens when the engine gets warm. It seems to run good at first start-up but slowly gets worse a couple miles down the road. Is this a symptom of a cop going bad? Maybe two? What is the best way to identify the bad?

 

It is possible for a COP malfunctioning when hot .
One simple way to find out is to buy one good COP ( Motocraft ) and swap one COP at a time until your misfire is gone (assuming only one bad COP ) .

How many miles do you have on the clock ?
when the plugs/ boots/coil springs changed last time ?

When a spark plug gap gets larger ,it takes more current to jump the electrods , then COP works harder and it gets overheated and that can cause failure .

Good luck,

 

I pulled and replaced all the boots when it started the problem a week ago. I cleaned the spring sockets and added plenty of diaelectric grease everywhere. I bought a new cop and now on my 4th swap out with no luck. I guess I will painstakingly go thru the rest of them over the course of the weekend. I betting that I have two that are bad and that is messing me up on the process.

 

I bought another new cop on the way home yesterday and this morning swapped out #7 cylinder and I think I have found the culprit. It ran smooth all the way to work. On another note, I'm pretty sure that when I swapped out #9 it ran better but still missing when hot.
I think my frustration in my process was that I had two bad cop's.

 

Backing up just a bit you say you couldn't retrieve a code with a scanner? Is the data link connector working? Did the MIL or Check Engine Now light come on?

I had a similar temperature related misfire with aftermarket COP's, overnight cold lower than 38* would cause misfire. Once engine was warmed and restarted the miss would go away, MIL still showing a fault. That's not unusual for cheaper COP's.

Another thing to check is the wiring harness connector as their locking tabs have been known to break either from old age or a heavy thumb. They can temporarily lose contact and throw a code. Replacement pigtails are available through most good parts sellers, I use NAPA EC259.

HTH

 

The COP assembly coil may not be the part that is failing. The coil may be working harder with a larger gap, but the spring may be causing higher resistance if it is rusty or the boot may have aged and have a split or thin spot that is arcing thru.
Our car was misfiring because of water getting on 2 cylinders causing the springs to rust. Did not throw any codes. I'm in the process of getting Torque Pro running on a Thinkpad PC to look for early signs of misfires. I've read that there has to be a certain number of misfires before a code is set.

 

Most hand-held scanners like an Actron CP9580 can read the misfire counter---its typically a pending DTC but does require a threshold be reached before it will throw a cylinder-specific code.