OBD II and the standard a/f ratio sensor

[SuperRetard]

I'm going to be turboing the 2NZFE, and I've been looking at simple ELM-stylee adaptors for my laptop. Now I've figured out that you can see pretty much anything that's got a sensor using the free software available for download pretty much anywhere.

However, is this data going to be any good for telling me what to do with my tuning?

For example, how does the toyota o2 sensor work? Are there 2? One upstream the cat and one downstream? How does the Toyota ECu decide what changes to make to the fuelling? Can I alter these changes through the OBD II interface?

It seems to me that the system just keeps moving from rich to lean constantly. And that the median is a fixed value associated with the voltage output from the sensor. So the sensor says 'too rich' and outputs a set voltage. Or says 'too lean' and outputs another. Is that right?

[yvvan]

The voltage range on the oxygen sensor is between 0.1 and 1.0 V. When the reading on sensor 1 (the one before the cat) is 0.45 V, then the A/F ratio is stochiometric, when the reading is below 0.45 V, the A/F ratio is lean, when the reading is higher than 0.45 V, the A/F ratio is rich.

It's the sensor itself that changes in voltage output, this is being read-out by the ECU which then changes, in accordance with it's mappings, the duration of the injection time, longer when the reading is lean, shorter when the reading is rich.

The voltage does indeed oscillate constantly between 0.4 V to 0.5 V, there is continuous adjustment from the ECU.

I have no idea as to what mappings you could change on the ECU through the OBD-interface, I know it works on certain cars, but have never delved into these things.

Cheers, Yves.

P.S. : change thread title please, thanks.

[SuperRetard]

Soz, dude! The thread title won't change...

I've bought an OBD kit, so the laptop will be my new passenger for a while.... ;)