Most accurate method is a direct AF sensor plumbed into the exhaust stream before any cats.

Tailpipe sniffers vary in accuracy, based on the method and dyno, but the good ones are fairly accurate, and certainly accurate enough to determine if you are running dangerously lean.

Sharif my man, I have no cats :) would sniffers be good enough?

Yes. :)

Finally!

http://www.the370z.com/tuning/13253-...tml#post360570

I thought most new cars have wideband sensors installed. My Dash Dyno reads A/F
ratio from three different sensors. The manual says that if a wideband sensor is not installed it won't give a reading.

yes our primary o2 sensors are wideband sensors straight from the factory thats why they are so expensive to replace.

Can't we use the stock O2 sensors on the manifolds for AFR readings then?