Hi,
Either the new sensor is faulty or not fully installed. That is what determines the sequence and timing of spark to the plugs. If you are getting a backfire and it started after the sensor was installed, those two possibilities are my first suspects.
Since it just started doing this, recheck your work. Make sure the sensor is fully installed and tight. Also, check to make sure the electrical connector and wiring are both in good condition.
If there are and you find no issues, my suggestion is to remove the sensor, take it back to the parts store, and request a new one under warranty.
Please understand, I know that I could be wrong. Not being there with you makes it more difficult to diagnose. However, this seems to be the most logical sense.
Let me know.
Take care and if I don't hear from you, have a great New Year.
Joe
Wednesday, December 27th, 2023 AT 9:13 PM