Smelly Odor from Gum Not Going Away After New Crown ?

My experience with re-treatment of old root canals is that they don't work very often. The odor is caused by the bacteria still present from the infected tooth. Since the bone is decaying (being eaten by the infection) most likely you need the tooth extracted. It is also my experience that you need to be cautious about grafting and placing an implant in an infected site. The "teeth in a day" approach will not work for this situation. A bridge or delayed implant placement and a new crown would solve the odor and decaying bone.

The Odor is most likely from bacterial infection of some kind.  It may be from a peiodontal pocket in the area harboring bacteria or if the tooth is decaying the bacteria will also emit a foul odor.  It sounds as if you have a combination of these issues.  Seek the advice of a Board Certified Oral and Maxillofacial Surgeon to help stop this process before it affects other teeth and surrounding tissues in your mouth

If a crown has an open margin, crack, and leakage of some sort the odor can occur. But you said, you replaced it and it did not help. So, either the new crown is still having leakage issues, or your tooth underneath is cracked below the gum line . If the latter, then you need to extract, place possible bone graft and an implant or replace the extracted tooth with a bridge.

Good luck