Hi Don,
White smoke is usually caused by poor combustion and is most common after cold start due to glow plug probs but as yours happens also when the engine is warm it won't be a glow plugs issue.
That leaves fuel contamination, coolant problems, injectors or low fuel pressure in the high pressure common rail.
As you don't mention hard starting or engine misfire when idling it is probably not a single injector failure.
Try cleaning the electrical connections: a. High pressure fuel sensor located at the battery end of the common rail.
b. High presssure regulator located just left of starter on back of HP pump.
I have taken Fuel pressure signal voltages from an identical engine which is operating normally:
High pressure sensor: voltmeter connected between blue/black cable and earth.
Ign 'on' engine off = 0.5v
Engine idling = 1.28v approx
3000rpm =1.96v approx
Take care when the engine is running.
Good luck.Dann..