OK its not just a single injector thats stopped working - you'd still get the engine started which one down or maybe even two injectors down.

The white smoke is vapourised diesel - which suggests although you got the engine to fire it wasn't running on all four cylinders. If diesel doesn't get hot enough to burn then it vapourises...

More questions:

When you say "diesel flow is perfect and very strong" how are you assessing this?

Are you 100% sure the injectors were put back in the same order as they came out (ie each cyl has the same injector in as before)?

Alex