38Chevy454
Give me a museum and I'll fill it. (Picasso) Give me a forum ...
Cars with two cylinder banks (V6, V8, and similar) have four O2 sensors. The upstream ones are which control the fuel mixture. The downstream after the catalytic converters is just for emissions to check the cats are working properly. The upstream ones will affect engine running and fuel mileage, the downstream do not. Being located in hot exhaust, the O2 sensors can be tough to remove after many years.DD has 4 - O2 sensors and 1 was faulty. Too much for me to do. Our "guy" checked it and parts/labor is a whopping $165...done.