Peter:
The vehicle is a Bosch common rail system so cracking injector pipes isn't really an option. They do tend to self bleed pretty quickly though providing the low pressure supply is good which it is.

Steve:
I was thinking around those lines. The immo light isn't staying on though and no immo related fault codes have been logged. I may look into this a bit further though and try what you suggested as I'm convinced it's electrical.

Aidan:
I have had each one out individually, turned around and re-plumbed into the vehicle and firing into a see through test cylinder. I can confirm they are all firing diesel. I have also bench tested the injectors on our Hartridge machine at pressures accross the board. All good.

I currently have the ecu away being tested so fingers crossed it may be causing the issues.