Ford F150 - #3 cylinder misfiring

my 97 f-250 is flashing a code it said #3 cylinder is mis firing i checked the coil its got a spark,same as the pluge.also when i drive it at 55 mph the motor shakes really bad,if any one can help me out thankyou

What engine? Post it in your profile.

I have a 1999 5.4l i have the same problem every few months, but usually not the same cylinder. I am too lazy to replace everything at once so i only do what misfires. Moisture i think is the problem. Sometimes if you just pull it out and place it back in, or switch with another cylinder it will fire right up. Its a huge PITA but I've learned to live with it.

Correct, do what it says and replace #3 coil.....

.
For reliability, I replaced plugs and wires at 90,ooo and my '98 4.6l runs fine.
.

Gotta have the reliability: On time, On target, Never quit.
.
Good luck.
.
.

If your sure the coil and plug is good,then I'd be willing to bet you have a broken valve spring or a bad valve.I know that's not what you want to hear,because that wasn't the answer I wanted either.If when your driving down the road and it feels like it kind a smooths out a little when your over 1700 rpms,or when you let it coast it feels like it smooths out,it's more than likely a bad valve or valve spring.
I've got the same problem with my 2001,I'm in the process of replacing the heads on my truck right now.once I have the heads off I'll post what happened to the # 3 cyl.in my case.For what ever reason there seems to be a problem with cyl.#3 on these 4.6L Romeo engines,if you look through the forum there seems to be alot of trucks with the same problem.