cm871 injector

[hct5]

having an issue with an injector. engine was running rough and dumping white smoke. did a cylinder cut out test number 6 was dead. also did a cylinder performance test cylinder 6 failed. everything in the overhead looked good and was in adjustment. pulled the injector and pressure tested the coolant system the injector cup is good and not leaking. changed the injector adjusted the overhead and still have the same problem running rough, white smoke and on the two tests stated above i get the same results. any ideas of what it could be? i double checked the overhead to just be safe.