Dear Blindboy,

Hope you're well and stay so. The soot deposited on the surface of the catalytic converter (cat) likely contains some un-burned gasoline, which bonds the soot to the rough surface of the converter's core.

A highly-polar solvent, e.g., Methyl Ethyl Ketone (MEK) might help to flush-out the soot. But MEK is very flammable and carcinogenic: gloves and lots of ventilation needed.

The cat will have to plugged at both ends, while the MEK works on the soot. So, the cat will have to be removed, one end plugged, and the MEK poured-in and the open end plugged tightly. Let the cat sit overnight. If the MEK is jet black when poured into a steel or plastic pail, then the soot has been removed. I'd repeat, to be sure. If the MEK is still clear, then it has not removed any soot.

Another possible way to remove the soot, is to heat the convertor in an oven. Ideally, if you had an old kitchen stove, with a self-clean (NOT continuous clean) feature, put the catalytic convertor in the oven and run the oven through the self-clean cycle. Temps rise to a tad over 900 degrees. That should cause the soot to "vaporize", i.e., to be converted into carbon dioxide.

I've never tried either of these methods, so do not know if they'll work. But the cost of trying them is low. If they fail, the cat sill has considerable salvage value, as the Platinum and/or Rhodium will remain.

Hope this helps.

Yours faithfully,

Spook