o2 sensor readings off the chart!

[vader t]

Hopefully you experienced tuners can give me a hand. The 02 sensor readings in my car always (WOT) in the 700 to 800 range and the mixture is rich. I'm wondering if it is way too rich. This is with about 24lbs of boost. The 02 sensor is brand new.

 

[bruce]

Originally posted by vader t
Hopefully you experienced tuners can give me a hand. The 02 sensor readings in my car always (WOT) in the 700 to 800 range and the mixture is rich. I'm wondering if it is way too rich. This is with about 24lbs of boost. The 02 sensor is brand new.

The oem style of O2 are a guess at best for AFR.
In back to back tests, mine ran 810mv at 12.5 and 11.8 AFR.

You tune for performance, not to get to a number on a meter.

 

[vader t]

Fair enough, I just wanted to see if there was anymore there? I want to have a roll cage (11's )

 

[kenmosher]

The "rich" indication is a good thing ... in relation to stoichiometnric (14.7:1). At WOT the mixture is supposed to be richer to provide cylinder cooling and enough fuel to make power.

As far as O2 readings ... as Bruce said, it's not an exact science, but it can be used as a gauge for tuning to make sure you are "in the ballpark". EGT, fuel type, sensor type, wiring, etc. can all affect O2 sensor readings.

I find with my car, it "likes" 730-740mv on 109 octane VP "Blue" and 1500 EGTs. On a really "good air" day, it needs 750s to not tickle the knock sensor.

On the chassis dyno several years ago, it made best power with those numbers too. I should learn some more soon when we put my motor on an engine dyno and play a bit too.