my truck shaking when i drive and the check engine light is on off and on

The expeditions have some commen problems that would cause this. The first thing you need to do is have it checked for codes. I'm sure there will be missfire codes (this is why your check engine lamp is blinking). Driving with missfires is not a great idea as it can destroy catalytic converters and internal engine parts. More than likely you have a bad coil (very common and not to hard to replace). If it's a spark plug these can be somewhat of a pain because they have a tendency to actually blow out of the cylinder head and or break while trying to change them wich requires special tools to repair threads in the head, good luck,

sounds like a misfire i would have the codes pulled