O2 sensor replacement & AIR question.

[Munch]

OK wise sages of the Barn... Can I replace the O2 sensor in my LG street headers without dropping the header?

Secondly: Does the AIR system (is that what it's called?) run all the time or just at start up until the engine is warm? I ask because if it runs all the time won't this send false readings to my O2 sensor? As I type this it seems to me that the pump would only run until the engine reaches a certain temp or the ECU would never get accurate readings from the O2 sensor but I don't know this to be true so I am asking you.

[Y2Kvert4me]

The AIR pump can run for a maximum of 4 minutes after cold startup, turning off once the PCM switches to closed loop operation. It will also turn off if engine speed exceeds 2825 RPM, or if temperature is below 14°f.

During the brief time the pump is running, the 02 sensors are expected to read leaner, this is how the PCM monitors the AIR system function, and how it can generate trouble codes if the pump or a check valve fails.

The 02 sensors during this time of open loop warm-up are not contributing to fuel trims. That only occurs once in closed loop mode, when the AIR pump is switched off.