Hello, I am John, a Ford dealer technician.
I hope I can help solve your problem quickly and accruately.
Is this a skip that occours all the time or is it just under load? How do you know it is number 4, did you check the codes? What was the code? Were there any other codes?
Most of the time when you have a skip on these trucks it is caused by either a bad plug, wire or coil. It can also be caused by an injector but this is rare. Being your truck is 11 yrs old it would be a good idea to do a tune up any way. Start with plugs and wires, if it still skips replace the coil. Worn plugs and wires are what causes the coil to go bad anyway. If it still skips replace the injector. But like I said, this is uncommon.
I hope this answer has been helpful to you! If you have any further questions please feel free to ask.
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