O2 sensor....Odd problem

Take it back to where the work was done and tell the you expect them to fix it for free since they are responsible.

O2 sensor bungs (the nut the O2 sensor screws into) are available as a repair part. They can cut the old sensor/bung off and weld a new one in. I believe that the 5.0 Mustang O2 sensor bungs are 18 MM thread.

Or you can get a die grinder or electric drill, a cylinderical cutter bit or 1" grinder stone. Grind the spattered weld off the old O2 sensor and try wrenching it out. Some heat applied to the bung (don't) heat the sensor body) will help in the removal process.

Die Grinder:
View attachment 175936

cylinderical cutter bit or burr
View attachment 175937

Do a Google search to find the above cheaply. Harbor Freight will have the die grinder. The cylinderical cutter or burr may be harder and more expensive to find. Small grinder stone can be bought from most hardware stores or home improvement centers.

Before you try and pull the sensor, check the ground wire. It comes off the fuel injector harness and goes back and bolts to the back of the motor. It maybe all greased up and dirty and not making a good ground. The wire is orange. This was my problem. After I replaced the sensor I was still getting a code. Cut the ground wire and ground it on the firewall and the code went away.

Basically a nut with the sane thread pitch as the sensor welded over a hole cut in the pipe.

See K&N/Oxygen sensor weld-on fitting (85-21688) | Exhaust Weld-In Bung | AutoZone.com


Part Number: 85-21688 cost $16

spark plug non-fouler worked for me. Just had to cut the end off, then weld the "nut" part to the pipe. A pair of them was $4.