I have a 2002 bonneville SSei that is experiencing a miss fire on cylinder #4. I have replaced the plugs, wires, moved the coils around and replaced the icm. Still misses. any more ideas?

Have you checked your injector? Check the path the plug wire takes. I've seen broken valve springs cause miss. Also try a compression test.

Listen to the injector on cylinder 4 with a mechanics stethoscope (try a wooden dowel if you don't have a stethoscope) and compare the sound you hear to another injector. You should hear a steady ticking noise as the injector fires. If you don't hear it you need to check if the injector is getting a signal. The easiest way to do that is to take an automotive bulb that has wires on the end that can be straightened out and stuck in a connector. Pull the electrical connector off the injector on cylinder 4 and insert the bulb wires into the body side connector. Have someone crank the engine and see if the bulb is lighting in cadence with the RPM'*.

If you are getting signal, but don't hear the injector firing, replace the injector. If you are not getting signal you have a bigger problem.

You can also try switching injectors with another cylinder and see if the misfire moves to the other cylinder.

Misfires on a single cylinder can be a bad plug, a bad plug wire, a defective injector, or a mechanical issue. If you don't fix it with the plug, wire or injector, you can narrow down the mechanical issue by doing a compression test on the misfiring cylinder, and/or pull the valve cover and inspect for any damaged parts in the valve train.

It turned out to be a bad seal on the injector. Runs fine now. Thanks for the input.

Good to hear you found it.