Ok I may have misunderstood your question Here is what you need to know on replacing the injectors. But with STC injectors There is a flush kit to clean them and than you can readjust the injectors. It is known as a flush and adjust.Cummins sells the flush kit.The smoking issue can also be caused by a bad STC valve. If you do proceed with a injector change than rebuild/ replace the STC valve. It should be rebuilt either way. These were a known issue with these engines.
To replace injectors
Remove valve covers
loosen the injector adjusting screw
move the push tube to the side and allow the rocker to be free.
remove the injector link on the top of the injector
remove the 2 injector hold down screws
use the injector puller (special tool) part number(NNN) NNN-NNNN/p>
lube the orings
install injector use a blunt object to seat the injector a snap will be heard and felt when the injector is seated.
install hold down and torque bolts evenly to 168inlbs
install injector link
align push tube with injector rocker lever and install adjusting screw.
ensure the push tube is properly seated in the rocker and cam follower
than adjust with the chart i provided before.
hope this helps