astra van smoking after new engine?

got a t reg astra van , its got the manual diesel pump from astra f fitted to it and was working fine until belt slipped and had to replace the engine .. now with new engine in vans smoking a lot .. timing is set up to run with manual pump but it seems like turbo isnt working either , its the gm low blow engine and its got my mechanic stumped .. tried injectors etc etc .. any help would be massivly appreciated thanks(ps turbo seems fine when checked )