What is the next step to find the route cause of a cylinder misfiring if a complete tuneup has been performed including spark plug wires must injectors be replaced?

In such a situation, it is best to recheck what has already been done: Were the cap and rotor both replaced? Were they the correct ones? I have been sold these parts that I was TOLD they were correct, only to find they were not. Even minor differences can cause problems. Also, check the tightness of the distributor as well as the tightness of the distributor shaft. Bad distributor bearings can cause the rotation to be out of round and cause problems.

Another thing to look into is the compression of each cylinder. Assuming that the plugs were replaced, were all of the OLD ones dry or were any "oiled up"?

With these points addressed, you may have to look into the fact that one of the injectors may be faulty. They operate on varying voltages and can misread the information. If you have a multipoint fuel injection, you may want to have the Computer diagnosed as well.

SOMETIMES you can use a strong additive like BG 44K that can clean clogged injectors. It can be found at NAPA Auto Parts and is a on the pricey side. BUT, if it IS a clog problem that this stuff fixes, you'll be getting off cheap! Good Luck!