Here is a short story for you.
Friend of mine went on a servicecall. When he determined that the coilwire was bad ( and he did'nt have an extra one with him ), he played the good samaritan and exchanged his own ( good wire ), for the defective one.
He proceeded to drive home, noticing an increasing powerloss at the end of his 50 mile journey.
Next morning his engine would not start.
Total melt-down of the catalytic converter from the constant misfiring with the defective coilwire.
Remember, an O2 sensor will interpret a misfire ( plenty of oxygen ) as a lean fuelmixture, and just keep adding more fuel.

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2007 C 230 Sport.