Hi Lawrence,
Sorry for the delay in responding
I've been thinking about this.
On the face of it, one of your injectors does look a bit suspect. When you had them out, did you replace the firewashers? They're the little domed washers that sit between the end ofthe injector and the cylinder head. They must be replaced whenever the injectors are disturbed and must be installed right way up with the convex face upwards. If they're missong or upside down they can affect the injector spray pattern.
White smoke indicates unburned fuel whereas a bad injector will produce black smoke. While smoke can also indicate low compression on one cylinder, low enough to not be able to fire the fuel charge.
It will be worth having the injectors out and stripping them and giving them a clean, especially their internal passages with an air-line, as I recall you said something earlier about black speks you saw when you popped the unions off.
If you do strip the injectors, be careful not to mix up bits from one to another so do them individually. Be extra careful of the needle lift sensor injector as it is dead easy to damage it when pulling this injector apart.
With a badly running engine, it will be very difficult to tell any difference in running when disconnecting the needle lift sensor.
If that does not go some way to resolving, I'll happily take a run down to see you as Berkhamstead is not far off really. Not sure when though, I'm pretty busy for the foreseeable...
