What causes only ONE cylinder to run rich?

[nimski62]

Thats not signifying only one cylinder is running rich, that is showing that wideband sensor #1 is running rich. Most likely there are two, one on each bank of 4 cylinders. #1 is probably the drivers side, #2 the passenger side, then there are also narrowband post cat 02 sensors which verify cat efficiency (presence) typically labeled bank 2, sensor 1 & 2. Normally with any wideband sensor codes, the sensor itself is bad and/or giving faulty readings. Locate the the plugs for the two sensors, most likely found attached to the firewall in a plastic holder underneath the coolant bottle. Verify which ones run to the two front (or wideband/pre cat) 02 sensors. They will be the same plug, normally 6 pin, just a different color. Switch the harness plugs left to right, right to left, and clear the code. Start the car and drive until the code reappears. If the sensor is bad, the code will follow it will then say bank 1, sensor 2 running rich. If the code remains bank 1 sensor 1, then it is something in that bank of 4 cylinders, again not signifying cylinder #1 specifically

Yeah but the 02 sensor is right! it is running rich on that cylinder bc when i pulled the plugs, that one was the only one running rich.. black gunky ass buildup. no other plugs were like that.

[A4ringedONE8T]

Yeah but the 02 sensor is right! it is running rich on that cylinder bc when i pulled the plugs, that one was the only one running rich.. black gunky ass buildup. no other plugs were like that.

Each cylinder does not have an 02 sensor, it has one sensor for a bank of cylinders. So the 02 sensor is saying that particular bank is running rich, not a specific cylinder

[nimski62]

Each cylinder does not have an 02 sensor, it has one sensor for a bank of cylinders. So the 02 sensor is saying that particular bank is running rich, not a specific cylinder

yeah its saying the bank is running rich.. i know and understand that.. so i took the 4 plugs out of that bank, and out of those 4 plugs, only one plug was black. signifying that was the only cyl running rich. the rest of the 3 are good.. like new after 24k.

ill give the 02 sensor thing a shot.. and my cars exhaust smells like SHIT after i go WOT. and my oil gets black as fuck in 200 miles and my exhaust tip gets BLACKKKK after 25 miles.