Kevin Xhaferri

I own a 2008 bmw 535xi I’ve had a bank 1 rich fuel system for as long as I can remember I changed coils, spark plugs, replaced injector seals and tested them with no luck as to figuring out why my bank 1 was rich I bought all 4 of my O2 sensors used and since then I’ve replaced most of them with completely new sensors but after doing some testing and unplugging my bank 2 downstream sensors the car no longer has a rich fuel system in bank 1 and has gained a lot of power I’m wondering if someone could explain to me why my bank 2 downstream sensor can cause a rich fuel system in bank 1 and hopefully this can help others with the same issue thank you guys