The slacken of the injector HP connection is the best wah and have a roll of Kitchen tissue handy to catch the drops.
This is actually best done under load so that a poorley set fuel pump doesn t mess up the experiment. IE run the engine in gear and then slacken of the connections one by one and retighten before moving to the next. If there is no change in engine note when one is slack and spraying fuel then that cylinder is not working. Next remove that injector and check you have compression in that cylinder . If lots of compression then it could be an injector problem or pump problem. If no compression then valves or rings.
You need to ensure the engine does not start so may have to slacken of the other injector connections and catch the fuel with tissue.