I believe there are two lambda sensors in the STi 7 & 8, one in the exhaust manifold and one after the turbo.
What do each of them do exactly?

I know that during closed loop operation (cruising) the one after the turbo in the pre-MY01 models was used by the ECU to optimise fueling for improved fuel consumption.

Rupert

 

Nobody knows what there for, but these cars are being tuned all the time.

I am getting worried :-((

 

The O2 sensor that has 4 or 5 wires coming off of it will be the sensor used for closed loop fueling. This is the wide band sensor that is accurate around 14.7:1 AFR. The other is used to test the efficiency of the cats and is a narrow band sensor. I believe it is the front O2 sensor that is the wideband.

 

Thanks mate

 

The one in the headers on the MY01 > is (according to Merv @ PE), a "Wide range" not Wide band (don't ask me the difference because I don't know ) and all the fueling is taken from that. The one in the centre section is there just to monitor CAT efficiency which is why you get a check engine light if you put a de-cat downpipe on it. AFAIK, this rear sensor has no bearing at all on the fueling.

Matt

 

I would imagine the wideband in the front only adjusts fuelling for closed loop as open loop would be taken straight from a pre-set map. It would be a bit dificult to adjust fuelling continuously on open loop I imagine

 

That's true but I have heard that all new "VW group" cars as Skoda Octavia, new A3 etc uses all the time the wide band lamda sensor for adjusting mixture!!!
JIM

 

Jim,
Does this apply to turbo's engines ?
It would be very surprising they remain close loop all the time...

 

Well I am not sure and can't confirm the above, is a Skoda mechanic that told me this story, does anybody know for sure?
JIM