[Obocecha]

I hope somebody can give me some insight to this problem. I replaced the factory coil at around 150,000 due to some misfiring and hesitation. Once removed you could see several cracks on the surface of the coil. The replacement coil was new aftermarket. Fast forward to about 175,000 miles. Car was running perfectly then out of the blue started misfiring like crazy. I happen to have a spare OEM coil on an engine sitting in the garage. So I swap it out with this slightly used factory coil. Car ran great for about a week then started missing again out of nowhere. So I decided to try the original factory coil again just to see what would happen. And surprise it ran great for about 2 days. Well today after work I started the car and it runs like crap. I checked the wiring harness and everything looks fine. The car is only missing on the number 4 cylinder. I swapped out spark plug wires and plugs but it made no difference. Now mind you both OEM coils have cracks on the side which could let in water and cause problems. I just find it hard to believe that 3 coils have gone bad within such a short time. Help please!?

 

[iminhell]

Well you are using used parts you know could be bad. But being it's a reoccurring problem with #4 it kinda rules out the coil being the problem.
This guy --> http://www.focusfanatics.com/forum/showthread.php?t=186343
Is having similar issue, different engine, but still.

 

[Obocecha]

I believe 2 of the coils have cracks right next to the number 4 post. Not sure if that makes any difference or not. I should mention that the aftermarket coil that was replaced wasn't firing on the #1 cylinder. The 2 OEM coils are not firing the #4 cylinder.

 

[WD40]

If there's a crack next to the post on the coil, it's most likely shorting out when it tries to fire that cylinder...causing...a misfire.

Tonight, pop the hood (in the dark) and fire the engine up.
I'll bet you'll see a pretty cool light show going on around the coil if it's cracked. []

 

[illinipo]

Sounds like a problem with the 3 small wires going into the front of the coilpack. Its a common issue.

 

[bluefront]

What plugs are in there? Bosch by any chance? What gap......

But I'd still try a new coil before going any further. Can't trust used parts like that...

 

[WD40]

Sounds like a problem with the 3 small wires going into the front of the coilpack. Its a common issue.

^^^Good point.
Obocecha;
If you find that to be a problem, there is a replacement harness (or coil pigtail) available from Ford to fix that:
http://www.focusfanatics.com/forum/showthread.php?t=185844

 

[Obocecha]

Thanks for the help guys. I checked the harness almost a foot back and didn't see anything wrong with the wires or connector. I know these coils are used so I'm assuming it was their time to die. Hopefully the new one will fix these problems.