Bad Coil Over Plug?

[Whimsey]

2005 4.6 Explorer with ~202,000 miles. All except coil 3 are original, ejecting spark plug. All of a sudden after a brief acceleration the truck felt weird and then the flashing check engine light came on. I back off the throttle and the CE went out. It would come on and miss again if I pressed past 2,000 rpms or 1/4 throttle position. Unfortunately I live in Sussex County NJ, the hilliest part of NJ. I did my best to speed down hill so I could use lighter throttle going up hill, it semi worked. I got CE and severe missing on the last uphill. I got home and checked with my Torque Pro and I got a P0308. I have a brand new Motorcraft spare coil with plug wire which I installed on #8, back plug on the driver's side I hope . It seems to have stopped the problem, at least locally on steepish hills. I also checked the spark plug and it was a perfect very light tan with no black what so ever and the gap is perfect and it's a Motorcraft replacement plug. I tested the old coil and the primary circuit is .5 ohms and the secondary circuit is 5,520 ohms, both seem ok per general testing specs, though I'm not sure about the Ford's specs. Can a coil test ok off the vehicle, run ok at low stress but fail at higher stress, ie more throttle and rpm?

 

[2EHA]

aftermarket ford 2 pin coils have a lifespan of about 10 minutes, making coils that work isn’t a trivial task apparently

i’m surprised the originals lasted that long

 

[bdcardinal]

Did it happen to rain recently? I forget if it was a thing on the Explorers with the 4.6 but the Expeditions and F-150s would have rain water cause issues with the rear 4 coils.

 

[Kestas]

Inspect the coil 8 for bulging or cracking in the case.

Switch it with another coil and see if the problem moves with the coil.

Otherwise there's a lot of information online discussing problems with code P0308 and Ford.

 

[Whimsey]

Did it happen to rain recently? I forget if it was a thing on the Explorers with the 4.6 but the Expeditions and F-150s would have rain water cause issues with the rear 4 coils.

We've had some heavy rains recently though I can't say for sure in this case. This happened on the return leg of a trip at appoximately 75 miles of the 100 mile trip and it was sunny and nice that day. I was just curious that it could fail in this manner, not totally, but under more "stress" and yet testing it off the vehicle it appears to be "ok". Oh well I only need to keep this vehicle till next May, maybe I'll buy another spare coil and keep the tools in the vehicle to change it if it happens again on another coil. I know the early F150's especially with the 5.4's were prone to shorting coils due to coolant leaks on #4 coil.

 

[2strokeNorthstar]

We've had some heavy rains recently though I can't say for sure in this case. This happened on the return leg of a trip at appoximately 75 miles of the 100 mile trip and it was sunny and nice that day. I was just curious that it could fail in this manner, not totally, but under more "stress" and yet testing it off the vehicle it appears to be "ok". Oh well I only need to keep this vehicle till next May, maybe I'll buy another spare coil and keep the tools in the vehicle to change it if it happens again on another coil. I know the early F150's especially with the 5.4's were prone to shorting coils due to coolant leaks on #4 coil.

5.4 leaks coolant into 2-3 from coolant crossover leak, 4 is from rain water, 1,5,6 from people washing the engine..... great design