Weak spark during cranking: Strong spark when running.

I'm still trying to solve my Explorer's random starting problem.

It always will turn over just fine, but sometimes it will not start. It does this randomly for no appearant reason. It may go for months or just days between incidents.

Anyway, I tried to see if it was a spark related issue by using a spare spark plug. I unplugged one of the wires from the spark plug on the engine and plugged the spare spark plug into it. I gounded the plug while someone turned over the engine. There was a VERY weak spark visible at the gap and the engine did not start. Later, when the engine started and I checked the spark by this same method. The spark was much larger and was easy to see and hear.

Is this normal or is it a sign of an electrical problem?

Thanks

Bill

I'm not sure of the year of your truck,but most are the same when it comes to coils. I would buy one coil pack and see if you still have this issue.PG