I just changed my plugs in my truck and put everything back together started it up and it's having a little shake to it. Then the check engine light came on so my friend brought over his scanner and it said misfire cylinder number 4. What can it be after just changing the plugs and the gap is correct.

 

Probably didn't get the plug wire on right.

 

You mean the cap that goes on to the top of the plug? Which cylinder is number 4? Where is it located in the engine compartment?