Suggestion. Get yourself a mechanic's stethoscope and "listen" to the mechanical click of the injector. Compare to the other injectors.
If no mechanical click heard, then then next attempt to isolate the reason to mechanical or electrical.
To determine if the injector is getting the electrical firing pulse, use a noid style test light across the fuel injector. The test light should blink. If no blink then the focus should be on the electrical connector, wiring, or PCM.
If a fuel injector problem is suspected, consider an injector cleaning/flow test service such as InjectorRX.com. Once cleaned and tested they are as good as new. Cheaper than new.
Another option is to buy some number of used units (stevew01) and have the replacements tested and cleaned. Then a known good unit will be installed.
Me personally whenever I have had fuel injector issues in the past have pulled all (8) and sent them out for cleaning/testing. To me it's about as much work to pull one as it is 8. IMO better to get it done right the first time and be done with it.
Swapping the COP is also a great way to isolate a possible bad part. The COP's are stupid easy to swap and the results are easy to see. Note, be sure to clean out the spark plug wells (moisture and/or dirt).