How to know which catalytic converter is bad on a 1998 ford explorer 5.0?

Answer 1

It's usually the primary or last one even if you have pre cats since it does the most work. if you have a code it will tell you which O2 sensor it is which will help narrow it down. You could pressure test fore and aft of the cat by drilling small hole or use an infrared thermo to see if it's running extremely hot or hit it with a rubber mallet to see if contents inside have crumbled. A rotten egg smell (sulphur) is another sure sign. i may be mistaken, but I think only the honeycomb in the "real" cat can create the sulphur smell. The main thing is determine cause of break down if it has happened. Usually car has to be dumping too much fuel to kill a cat, which means something else is not kosher with mixture probably something in engine management controlling ratio.