Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
Installed rebuilt motor because timing chain went and messed up motor installed 6 factory fuel injectors and installed new bank 1 cat that was bad and new o2 sensors on that bank but I’m having po2099 which is bank 2 new mass airflow sensor installed car is running beautiful I’m wondering if the bank 2 cat is bad or the 02 is bad
It's very possible you have a bad downstream O2. But before that, it's important to check for exhaust leaks between the upstream and downstream sensors on bank two. Light air pressure in the tailpipe and soapy water is the preferred method. Smoke (or just listening for leaks) may not expose pinholes or small cracks.
I know you said it runs great, but I'd still say check your fuel trims anyway.
If you find no leaks and the fuel trims look good, I'd say go for a downstream O2.
