Helpppp agu not firing on 4th cylinder :(

Hi i wonder if anyone has any ideas. I changed my fuel pump for one out of a low mileage golf and my car was running fine, even better than normal tgen drove it for about 25 mins then it started misfiring. I limped back home and swapped the fuel pump back over thinking it was that but didn't change a thing. I swapped the coil pack from 4 to 3 and then to 1 and still no joy. Also cleaned the injectors and changed the seals and filters and no change. Also just done the fuel filter with still no joy. Oddly though while driving uphill in i think it was 3rd gear it would vibrate a lot and heard a relay clicking and the dash lights flickers. Do you think a relay could be causing it not to fire on all 4?? Also my fuel pump relay is 167 not 409

Wen i remove the plug for the injector on the 4th it stays the same where the others get worse. I think its the fuel pump relay so gonna try that first and hope it is especially as i heard a clicking sound behind the dash or is there an ecu relay also. Might be 1 out of the 2

Ok i'll see if i can get one to test it before i buy one