if you run a DERV with very little or no fuel you can end up with airlocks in the fuel rail and such components.
if it is that, then you could try what i tried on my mates transit.
finding the closest point to the head of the engine, where the diesel goes into the injectors and undo it half a turn or so, so it can leak. (one at a time)
crank it til it pisses over your engine a little bit, and retighten, you might need some rag in situ for this!
do it for all four injector lines and you should've bled the system through