this is the brilliant designed setup where the injectors get wet and they corrode into the block
Its all perceived doom and gloom with these, Timing Chains, Gearboxes & Injectors ...
I drive the same vehicle every day, same 2010 model M9R and 173k miles on it now - Good Van, I expect to get another 170k before I think about sacking it off.
It is not because the injectors get wet that they corrode into the head. My scuttle drains have been kept clean from day one and upon removing the plastic cover over the injectors it was bone dry in there, no evidence of water and the injector seal had not failed either causing blow by. Yet it took a specialist 3 hours with hydraulic apparatus to remove an offending injector. It snapped in 3 places on its way out.
That is 3 hours, plus I had to remove the scuttle, wiper mechanism, Airbox, its frame, Induction pipes, injector cover, manifold etc. before he arrived so he could hit the ground running.
I think that they are just a very tight fit, 2 different materials too close to each other and then put in an oven to bake, so to speak. Not unlike the Old Jaguars and Triumph Dolomites of yesteryear where the Steel Head Studs would weld themselves to the Alloy Head.
had planed a leak-back test but i would have to remove inlet manifold to connected up pipes and tubes
Indeed, No walk in the park! Any work on these vans seem to involve taking the front off or at least getting the Air Box and its frame out of the way. Indeed a PITA. Getting at the ECU involves removing 2 Shear Bolts.
Non Intrusive testing on these is a Non Starter
Moving forwards there will be Smooth Running Values for the injectors which will often give a clue.
Also note that Injector 1 will be a Flywheel end - or not dependant on Scan Tool.
CKP with a Math Channel riding on it will be as definitive as you can get, there is no option with these for Swaptronics. For a leak off test, which should be done although there is no short cut as you already know.
Whilst you have access you could do an insulation (internally short to ground) test with a Bosch FSA 050 or similar set at 100 - 150v. Yours will be an electrical/insulation fault as mechanical failure will normally throw a P0300, P0302 Misfire DTC.
These are notorious for Injector failure displaying the very symptoms you describe, and the other 3 injectors will quite likely fail soon - Domino effect.