O2 Sensor code long term effects of not fixing '04 LC (1 Viewer)

[LC neophyte]

'04 LC 123K-- Our mechanic replaced the full exhaust including cracked manifold, but not the catalytic convertors. We drove it for about 5,000 before getting it repaired. This is my daughter's LC, so I did not receive an after fix performance report yet.
MPG had gone from 15 to 9, and of course the muffler was shot and very loud.

What are the long term effects on the engine if you drive for 5,000 miles before replacing the exhaust system and O2 sensors? I would like to understand what they actually tell the engine to do. I understand that there are 2 on each side. One before the cat and another after? I don't know which was triggering the check engine light.

In my case, with a cracked manifold, I assume that more air was being mixed with the downstream exhaust gases which told the sensor that the fuel air mix was too lean? Does the feedback loop then adjust the fuel/air ratio at injection? Now adjusting the mix to be too rich which will gum up the valves and head?

 

[OwnerCS]

I've seen people neglect O2 sensor codes on Hondas that allowed the engine to run too rich. That would burn up the catalytic converter. So they had to replace the sensors and converters. In this case, I think they ran for over a year -- much more than 5,000 miles.

I would just fix the exhaust and O2 sensors and see what happens. I usually replace O2 sensors after 150,000 miles.