Hopefully a quick one - what's the voltage range on the lambda sensors fitted to our cars & what's lean vs rich etc.? Thanks!

 

Hello Zig,

A discussion about interpreting O2 sensor readings might not be a quick one!

However in a nutshell, the voltage readings from the sensors "switch" between zero and about 1.2 volts a few times every second.

Lean vs. rich is usually interpreted by the Long-Term Fuel Trim, which comes from data collected from the O2 sensors over time. In general, LTFT value in the negative range indicates rich running, while a value in the positive range indicates lean running.

Much debate usually ensues about the meaning of these readings and how they relate to the health and well-being of the engine.

My two AJ16s seem to settle into the range of -3.1 to -3.9, according to my generic scan tool.

Others here might provide more insight...

 

That'll do nicely! Thanks... Now I just need to work out how to get the LTFT out of my OBDII dongle - don't suppose you know the PIDs do you? It was looking at the STFTs that made me want to check the O2 sensors were doing what they should - seems they're probably ok.

 

Just getting my head round what it's doing - I'd be much happier if I had some carbs to balance, but hey!

STFT goes to zero at ~WOT. Why does it do that then?! I presume there's just a pre-determined map for those conditions?

 

It's probably going open-loop. You can't trim the fuelling if you aren't listening to the lambda sensor so it makes sense for the ECU to report zero.

There is a PID for open/closed loop - at least, I can see it on my Scangauge II.

Edit: I use the PIDs from http://www.scangauge.com/support/x-g...-vpw-vehicles/

 

Yep, it is indeed... so assuming it's supposed to do that, why??

Thanks for the link!