A failed catalytic converter affects engine performance and fuel economy. With a plugged converter, pressing on the accelerator does not increase the speed. The engine backfires, and the car jerks while driving down the road.
Converter problems make it more expensive to operate the vehicle. A rough-running car requires more fuel to go the same number of miles. A problem with the catalytic converter often causes an error code in the vehicle's onboard computer, which illuminates the check-engine light.
One method of checking for catalytic converter problems is to remove it to see if the engine continues to backfire. A second method is to disconnect the oxygen sensor. If either solves the performance problems, the converter requires replacement.