I appear to have a problem with my C20 XE

My car seems to be going through plugs for fun, I started it up on Saturday left it too idle up to temp with no probs at all, Went back to it today and it's running on 3 cylinders !! Changed the plug for another and back to 4 cylinders !!

Now when I try the dead plug in a plug lead with the engine running there is a really good spark at the plug !! I would have though there would be no spark if the plug was dead !!

Also with the engine running on 4 cylinders, ITB 3&4 closest too the flywheel appear to be doing the majority of the work, What I mean by this, If I disconnect a plug lead on say cylinder 4 the engine really dies but if I go to cylinder 1 and do the same it hardly makes any odds ??

I have balanced both banks of bodies to each other, Im at the stage where I'm at a loss as I don't know where to go next, My only unknown quantity is the injectors. I've cranked them over into milk bottles and the quantity of fuel was the same, I've checked resistance at the injectors and there all bang on.

Can you try swapping the injectors from 1 to 4 and then disconnect them one at a time to see the difference.I had a misfire on idle that wet away as soon as the revs were increased and fond it was the throttle bodies slightly out of balance by just enough to affect it at idle I increased the opening by a small amount on no 1 cylinder and it cured the misfire
Paul