Originally Posted by 200two-zx3
You are 100% right except you left out that when the and down stream o2 sensor detects high emissions it leans out the fuel trim which will cause poor performance. Also whn the enginelight comes on due to o2 issues the computer turns to a preset loop.
Yes, and in Fords it is called '"limp home mode". If a $20 o2 cheater is installed the ECU will never detect an issue or enter the loop.