Isuzu no start
 

Hi to all, very much a newby here and am already asking for help! If this is posted in the wrong area I apologise and would ask the moderators to move it to were it should be . I have looked but have not found a place for technical help. So here goes I have a 2007 Isuzu 250 fleetside with a compensator [sales talk for a small turbo charger] 250 Kilometers with fair reliability and maintenance, recently became difficult to start have checked all the norm, glow plugs etc battery and starter very strong ie sufficient cranking speed.
The red herring is that the truck now will not start, but if pushed starts immediately hot or cold! will only start when cranked if ether based "quick start" is used with consequential knocking. I am a petrol mechanic but have a little diesel experience but this has me fooled.
A booster electric fuel pump was fitted to try and help the existing lift pump to no avail. Parts and info are very difficult to come by, we are very rural and agricultural which does not help the case. Any help suggestions would be appreciated.

With Thanks Golfpin