In my last dyno session; a strange thing observed:

The wideband readings were 0.4-0.7 richer than the back sniffer readings at the same time, same test. Did you ever observed this? or it is just a simple calibration/misreading issue?

 

your wideband is more accurate then the back sniffer as its closer to the engine (so it has less time to mix with small air particles like the rear sniffer would).

 

Yeah, when I was at the dyno they used the sniffer and the car was definitely running richer than what they were seeing on the dyno... Rich enough that the tech thought my plugs were going bad so I swapped em out with iridiums and the car still sputtered.. My afr's on the dyno were flat 13s real smooth afr curve. I will definitely be going back for another tune once I get a wideband.