Ok... plot thickens.
I'm leaning towards this now:
6. It's already in limp mode for unrelated reason/ongoing fault therefore the above is all good but irrelevant and getting overriden by current state.
Specifically, fly-all boost pressure in intake (turbo works though)
Reason ( correct my potentially biased thinking please):
I went and bought a SaaS 30 psi boost gauge.
While examinining where to fit it I found this tap on top of the intake mainfold:
Not a fit, but as I did with disconnecting inj #1, I loosened the bolt creating an artificial leak... (blew and lost the bolt in the process though, thus far). Principle of either fuel, air, or spark missing ( last obviously not applicable to this!)
No change in behaviour with or without that in place!
So I think the turbo hoses, intercooler and possibly turbocharger comming off next... As little as I know about diesels and turbo, that's definitely consistent with a leak
R