Might it be possible, to test to see if a fuel injector is putting fuel into the cylinder by removing the spark plug, starting the engine and watching to see if fuel blows out?

 

Possible, probably yes. Safe, probably not.

I?ll suggest an alternative. Leave the plug in but removed the plug wire from it. Run the engine for just a second or two. Remove the plug and see if it?s wet. This won?t be perfect. The cylinder may draw in fuel from the other injectors, especially if your engine is pre-SEFI. However, if it?s really wet and there?s a strong smell of fuel, the injector is probably opening.

 

That's a better idea.