Crazy,
If you want to find out if an injector is firing, get a long wooden dowel or screw driver. While the engine is running, place the one end of the dowel or the blade end of the screw driver against the metal part of the injector. Place your ear against the other end. Along with various whirring engine noises, you will hear the ticking of the injector.
You can also use this technique to listen to waterpump bearings, alternator bearings. I've used it to locate a tapping hammer on the other side of a concrete wall.
An injector also will sound different if it is not injecting any gas such as when a small particle has clogged the inlet port.
Tom