Audi 90 2.3 E NG quattro runs only on 4 cylinders

Hello guys, I recently got the problem that my second cylinder has said goodbye. Ignition sparks are available on all 5 spark plugs. Also all spark plugs are ok. I just called Kleinheribert and now I also think that the injection valve has said goodbye. What are your opinions? I am grateful for any help… Greetings Tobi