Downstream O2 sensor damaged by running too rich?

[1998rollover]

1998 Mountaineer V8. Changed bank 1 downstream sensor that was damaged. Ran fine until both upstream sensors completely quit so it would crank the fuel trim up to full rich.

So I replaced the other three sensors. Now it's doing both 0171 and 0175. Bank 1 alternating between too lean and too rich.

Downstream sensor just crudded up and will eventually clean itself or do I need to replace it again?

 

[koda2000]

1998 Mountaineer V8. Changed bank 1 downstream sensor that was damaged. Ran fine until both upstream sensors completely quit so it would crank the fuel trim up to full rich.

So I replaced the other three sensors. Now it's doing both 0171 and 0175. Bank 1 alternating between too lean and too rich.

Downstream sensor just crudded up and will eventually clean itself or do I need to replace it again?

The downstream O2 sensor monitors catalytic converter efficiency. It could be the cat is not working very well, or maybe the sensor is all sooted up. You can try driving it for a while to see it things clean up. I think they make a chemical you can add to your fuel tank to help clean things up too. I don't know what it's called. I imagine most auto parts stores would know.

 

[lobo411]

Have you checked for gasket leaks, possibly fouling the sensors?

 

[1998rollover]

No leaks. Have recently done exhaust work, changed upper intake gaskets while installing new injectors and fuel pressure regulator.

The bank 2 codes haven't returned since changing the other three 02 sensors.