Ed- correct me if I'm wrong- this is how I diagnose ign/ fuel injector issues:
engine has miss- determine which cyl is missing.Then swap ignition wires to see if miss stays on this cyl or follows wire. If stays on this cyl, then swap spark plugs & do the same test again. If still stays on this cyl, then swap fuel injector & test again.

This is now the 3rd time I've had a service call for this unit, done the above procedure & have the miss follow the injector. The first time it happened, I was given permission to replace all 4 injectors. Unit ran good for about 400 hrs then began to miss again. The second time around, I was only allowed to replace the faulty injector. Within a month each of the remaining injectors needed to be replaced, 1 at a time at the customers request. That was about 500 hrs ago.