I have a BMW e92 2.0l car, living in the UK. I've been trying to get my head round how the wideband sensor works. I have 2 banks with pre and post o2's on both banks. I've noticed that the post bank o2's are a 0 to 1 volt and I'm guessing that these are narrow bands. They seem to be mirroring the widebands at rich and lean. Is this normal or should they be steady mid range with adjustments with lean and rich conditions confirming good cat operation. I hope this comes across clear. Thanks.
Unless you really max out the fuel trims rich or lean artificially you shouldn't see as much change in the post cat O2 sensor with a wideband upstream sensor compared with a normal Zirconia sensor wideband Titania sensor output works in the opposite voltage way round.
Although it won't confirm calibration accuaracy Wide band sensors keep pretty close control of the air-fuel ratio, the usual quick test on a wide bad sensor is what I call the "Dippsy Doodle Test"that is to quickly floor and instantly release the throttle pedal.
You should see the air fuel ratio instantly spike rich (low voltage) and when the pedal is released go instantly and very briefly lean (high voltage) then very quickly damp down to stochiomectric. The recover time to settle back to stoichiometric varies between manufacturers and models.
Unless you artifically introduce extra fuel or introduce a vacuum leak effect on the downstream sensor should be not as pronounced compared with a conventional narrow band upstream sensor.
" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)
Thank you for your reply and information you have provided, very grateful. So my downstreams follow rich and lean with the upstream's but in opposite voltage, equalling defective cats. Am I correct?
Yes rich and lean are reversed from what a conventional O2 produces but as with old style sensor.because the cat stores oxygen there should be a distinct time delay between forcing the upstream rich or lean and the change reaching the downstream sensor.
" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)
So just to confirm, am I right in thinking that I should be seeing the downstream o2's pretty much near stoic (straight line) with adjustments to rich and lean?
