Originally Posted by EC_Tune
Bill,
I've seen quite a few widebands do what you are reporting. There are some that are just not accurate at stoch. My PLX was probably the worst offender: 15.3-15.7 at Stoch on a lot of vehicles not just one. I've had exceptional accuracy with my DynoJet: within a tenth at stoch, that's as good as the sensor. The AutoMeter seems to be pretty accurate as well. NGK: Haven't used one yet but from all reports it's very good.
My only beef with some of the displays is that it's digtal. When I'm tuning I look for movement and a digital display is always moving so it's more distracting then helpful. More options on controlling the "LED rich lean" displays would be welcome.
Regarless of anyones pet theories, narrowbands (lambda sensors) switch at Lambda 1.0 (14.7 for gasoline). That's why the OEM's use them, they don't deviate, even with temperature.
Can big cams affect lambda sensors? Not so much on the exhaust side but on the MAF end when the MAF is too close to the throttle (Camaros have it the closest of the V8's). The early & late (not card style) MAFs measure air in both directions so if you have a big cam and a close MAF you will get fueling errors because the MAF doesn't know direction, just flow.
Are there areas where they are inaccurate, yes, generally at very low MAP, when you get big cam idle missfires, or if there is excessive oil present in the exhaust.