Timing is off, misfiring spark plug, or overly-rich fuel/air mixture. This will ruin you catalytic converter.
bills pipe
in the exhaust pipe
That's all down to how hard you run the engine. They can get glowing hot up by the exhaust ports.
in the exhaust pipe
one is located in the exhaust pipe under the manifold the other is located behind the catalytic converter in exhaust pipe.
in the exhaust pipe some maybe in the exhaust manifold for 4 cylinders
ther are 2 oxygen sensors, an upstream and a downstream . The upstream is on driver side of engine exhaust and the downstream is back of catylitic converter agin on exhaust pipe.
In the exhaust pipe, at the back of the engine.
in the exhaust pipe just below manifolds
They are in the exhaust pipe system, There are none after the muffler.
Right below the engine on the exhaust pipe.
There are two in the exhaust pipe behind the engine.