My 2000 XJ8 is going through 13 mpg after one of the ignition coils went bad, I think I may have killed one or more O2 sensors to to misfire and running rich for about 2 weeks waiting for a new coil, would anyone know if I only need to change the one O2 before the cat or do I need to change all of them? There are 4 am I correct?

 

More likely the catalyst could overheat on the side with the failed coil, but I wouldn't worry about it until after I replaced the coil. I can ship you a good used one tomorrow for cheap. Send me a private message if that will help you out.

 

Thank you, sir, I have already replaced the coils (no7) but like I said, the mileage dropped since before coil failure from 17mpg to 13 mpg. I think running too rich for a while killed my O2 sensor...
Alan.