Nissan interstar diesel problem

[arty21]

My nissan interstar diesel threw a cam belt over 2 weeks ago. A mechanic took on the job and stripped the head. No valves bent because the cam shaft has shear bolts (apparantly) Mechanic builds up the head and after 2 weeks gets new shear bolts finaly finishes the job and tries to start the engine. Engine wont start so he tried easy start and it fires for a few seconds and then belches out black smoke and stops. I thought it might be pump timing but suggested it to him and he said the timing is fixed and cant be adjusted. he now says it possibly is the fuel rail pressure sensor. The van drove realy well, with no starting/smoking problems before the belt snapped. Any suggestions on the possible problems.
Apparently after a days work on it the mechanic has informed me he has got the engine running on full revs but as soon as this is released the van stalls again.

Thanks for help

John