problem could come from many directions....
continuous blue smoke.....typically burning
oil.....
white smoke....most often is steam....can come from worn gaskets, pinholes in
exhaust systems, etc...
black smoke....unburned
fuel...
could also be a mixture of all three....grey/white....oil/water (steam)
no, you can't clean injectors yourself....you need to remove them and take them to a
diesel shop, where they can check them.
you can try additives, but I've never come across any that were much good....
but, if the
engine is running, and not producing too much smoke, it's not the end of the world either.