Nothing I'm too worried about but it leads up to my question.

I have an '09 JCW with low mileage, running a stage I alta tune. When I had my riss racing catless downpipe on the car, it seemed i was running very rich. I know that not having a cat increases smell/sight of exhuast, but i was wondering....

....does the readings of the O2 sensors effect how the ecu adjusts AFR?

 

Absolutely. The pre-cat oxygen sensor is reading the fuel trim due to combustion.
That voltage is interpreted by the ECU, and the impulse length of the fuel injectors are adjusted accordingly.
The post-cat oxygen sensor is checking the efficiency of the catalyst.

When you didn't have a catalyst installed, you were smelling unburned hydro-carbons and sulphides.

- Erik

 

well i meant more specificially does the secondary o2 effect it at all.

the o2 sensor up top shouldn't have a different between downpipes....

 

No, the post-cat oxygen sensor has no effect on fuel trim adjustments.
The post-cat only checks the sanity of the catalyst; nothing more.

- Erik