BMW 318 X reg estate. Not firing on no 3?

Hi, have a BMW 318 estate. Missing on no 3 cylinder. Have transposed the injecter from 1 to 3 and no difference. 12 volts feeding to all 4. When taken out and earthed no 3 plug firing. Have checked the arc from coils. Fuel going in and dump working. Driving me up the wall! Any advice........