The O2 sensor in most cars is a 'narrow band'. It basically tells you if you are running at stoichiometric (roughly 14.7:1) or not, to satisfy the emissions control equipment. Running against this sensor is called 'closed loop' operation.

When you stomp on the pedal, and hopefully get a reassuring push back into your seat, you are operating 'open loop'. The ECU is trying to guess at actual airfuel based on things like air flow. So the values in the fuel maps are really just guesses, rather the values are entered as "AFR" or not.

In a turbo vehicle in particular, WOT air/fuel mixture is a balancing act between cooling and power. Knowing where you are actually running becomes critically important in performance tuning - especially if you starting doing mods to injection, induction, or exhaust.

In addition to now being a 'core metric' (having largely replaced EGT, which used to be used to try to determine actual lambda/AFR) for performance tuning. A wideband can potentially tell you other things as well. For example, I see even single ignition misses as clear spikes, and detonation as high frequency ringing (helping me distintuish between real and phantom knock counts). But these things are secondary. Even if your wideband or sensor location do not give them to you, you are still getting a critical performance measurement.

-jjf

 

isht.... I'm sold.... looks like i'll be picking mine up soon......

 

Excellent information, thank you for taking the time to type this out. It really helped to clarify, at least for myself, the proper steps in which I would like to go in my tuning. I knew I wanted to log my data and build from there, so I guess going with a wideband and tantrix cable will be one of my first steps.

Thanks again.