BMW Repair: Loss of power and engine vibration, bmw 520i, engine vibration

Question
Hi there,
I have 1992 BMW 520i with M50B20 engine. Noticing engine vibration and loss of power but no rev jumping or smoke from exhaust and engine starts fine. Ignition coil disconnecting shows that 4th cylinder is not firing at all. Switching coils still leaves it at 4th cylinder and removed spark plugs confirms same as 4th cylinder spark plug is wet when others are dry. Tried swapping spark plugs but problem stays in the same place. Going mad as want to keep this car (my first BMW). Can you suggest where else to look. Someone said that injector might be the source of this but I have no clue how to remove them to check it. Any help will be greatly appreciated.
Marius

Answer
Well you seem to be able to switch parts well enough. I think you should do a compression test.Then if that doesn't give you any satisfaction a Cylinder Leak down test,that will help determine where you need to inspect.An injector could be the cause but knowing if the engine is mechanically sound is the first step.