2006 Vauxhall Astra astra 2 litre turbo design question

hi I have a Astra 2 litre turbo design it starts every time and when its running it makes a loud tapping noise drivers side, top end, white smoke with the smell of petrol coming out of the exhaust, I've put it on a dialogist and it come up with misfire on cylinder 4, I've checked the injectors and are sparking and the gasket looks brand new.
Thank You