Since your injectors are fired by the pump and not by the cam or hydraulics I don't see any reason that they wouldn't fire when removed from the cyl. If you do this be VERY VERY careful not to put your hands, fingers, or any other body part near the business end of the injector. Diesel injectors spray with a pressure of about 3,000 psi., and I imagine that gas injectors operate at about that range. It will penatrate your skin, and cause problems that you can not imagine. Another problem you might encounter is an instant fire. You are dealng with highly vaporized gasoline in an area that contains the possibility of sparks. If it ignites it will make a flash that you (if you, your car and garage, survive) will long remember. Best bet is to take the injector to a diesel injection shop and have someone 'pop' them for you. They can test the pressure at which they pop and examine the spray pattern. If you have a bad one they might have units that are cheaper than the MB shop. If not you might be able to find them on line. Good luck.