My 2003 Ford Ranger's #4 cylinder is not firing.

What is your question?

I replaced the plug and plug wire. Where should I look next? Actually at the time the #1 & #4 cylinder's both were not firing. I replaced all the plug wires and the #1 came back but not the #4. I then replaced the plug on it and had no luck. By the way the engine is a 4 cylinder.