O2 sensor question

[vancouver86/911]

The manual says to set the air/fuel mixture with the O2 sensor unplugged and at idle. What happens to the CO reading when the O2 sensor is hooked back up, does the CO level reading rise or lower or stay the same while the car is at idle?

[vancouver86/911]

bump

[Bob Kontak]

From reading here, setting the CO at idle (w/o O2 sensor hooked up) when cold is to provide the best setting for emissions when the car is first started. Car runs for a bit before the O2 sensor warms.

So, plugged back in, the O2 sensor is warm enough to activate and sends from 0.1V to 0.9V to the lambda brain under the passenger seat depending on how rich or lean the exhaust is. Lean = low voltage. Let's say it senses lean. The brain tells the frequency valve to reduce the fuel control pressure and that allows more fuel to flow through the injectors. However, the sensor will soon sniff a little bit rich (e.g., 0.7V) and the brain increases control pressure to provide less fuel to the injectors. This cycle continues when your car is in this lambda system "closed loop" mode. You can actually hear the cycling at idle when the system is functioning. The voltage is never in a constant state at idle but is always too lean or too rich within a few tenths of a volt range.

I believe the system stops functioning when you reach a certain percentage (35%?) of throttle but then reverts to closed loop when you slow down.

There are others (I like psalt's descriptions) that may provide more thorough info you wish to search on the member name.

[RWebb]

IIRC, the CO ought to cycle as the ECU adjusts things around based on the lambda reading - overall it should be lower