Was just doing a few notes for a customer and though would share here for young playerz
a really common thing I see in dyno shopz is the kuntz have zero idea with how the actual oxygen sensor worx
the oxygen that goes into the cell arrivez there via the cablez (Internally through the insulation and wire comes out at end where the wire is open to atmosphere !!!) so say if you have an engine bay fitted ECU then this is where it pullz the reference AIR from !!!!
it DOES NOT!!! come from the gasket end of the sensor as some dumb kuntz state on arse tube or arse book
this is why professionals like life racing put a boot on the end
Now sources of leaks can be a faulty connector gasket which allows ambient air to come in from another source like the engine bay not to mention if you have shit wiring damaged insulators etc then sans same gayness. This posses then a really big issue as many cars these days are fitted with lebo flapz or screamer pipez or just flat out aidz instal with vbandz that leak more than Elton Johns arse.
When you have this level of contaminated air recirculating around the entry point for reference air that the sensor uses to then work out what the oxygen level is in the exhaust you can easily see how fucked up your readingz can become !