please help me

Hello, my 2003 year discovery 2 has 4.0 engine. The car has hunting. At high RPM the receipt of engine check is flashing and is loosing power. I have changed spark plugs, spark plug wires,ignition coils, injectors, fipl,detonation sensor but it is not fixed.when I plug in OBD it writes sometimes about second barrel and sometimes about seventh barrel. It shows problem of differrent barrel every time.Sparks are getting black. Plese let me know if anyone can give an advice. In my country noone could find out the reason

It would help to have some history.. When did this problem start? Did anything happen or did you do anything different just before the problem started? It may be as simple as poor fuel and filling up from a different filling station so going back over time helps.
Also re-post this question on the forum for Discoverys as it will be read by more people who are experts on that vehicle.