Ignition Coils

If it has a noticeable miss that you can feel or hear, you can use insulated pliers, and pull one wire at a time and see which one makes no difference, a scan good tool would reveal this problem, you would be able to see the cylinders firing and fords wds can do a stress test on the coils,
caution when pulling plug wires, dont touch metal, and use the right pliers, coil spark may not seem like much but it does sting pretty good

If i'am not misstaken each cyclinder has a coil over each plug. A lot of times moisture will collect inside the holes where the plug boots are and will cause crossfireing in the hole only way I know to check them is to pull each one and check for moisture if engine has been washed at anytime that is a sure fired way to get moisture. NOS 8)