John,
You don't seem to be having any luck. Like many others I would check the air supply first, since you have been in the mud I bet! If OK I would check fuel supply at the engine, just prior to the injector pump but after lift pump, on the low preasure side. This would allow you to rule out tank breathers and lift pump. This would be the easy things. After that it could be like mine, manifold air leaks and a lot of other things as well.
When did you have the timing belt last changed?
Hope to see you next week.
Regards
Peter