Did he discuss with you WHY the cat might have become clogged?
The catalytic converter basically consists of a ceramic honeycomb sputter-coated with platinum-palladium, a rare metal in the rhodium family. When this metal is heated up and NOx comes in contact with it, it causes the nitrogen and the oxygen to seperate. The oxygen is then used to allow carbon monoxide (CO) to grab an extra oxygen molecule and become carbon dioxide (CO2). Hot enough, it also allows some unburned hydrocarbon molecules to seperate and bond to oxygen atoms, becoming CO2. this is often referred to as the “second burn”.
A catalyst by definition causes a change without itself changing. Unless it’s coated such that the NOx cannot come in contact with the platinum-palladium, or it’s physically damaged such as the ceramic substrate crumbling, it continues to do its job.
Since the catalystic converter is the next operation after the exhaust valve, and is in the exhaust stream, the only way this could have gotten gumped up like that would be if coolant got ingested into the engine and somehow blown through the cylinders onto the catalyst. I’ve never seen it, but it’s theoretically possible.
Honestly, since he showed you the gump, I’d consider just replacing the whole exhaust system. I’m sure some of the gump might have gotten into the baffles and muffler too. I cannot believe that a mechanic cannot find an exhaust system for a '99 Civic. If the rest of the car is in good shape, it may be worth fixing.
Thanks guys. We got a new catalytic converter and replaced some ‘squishy’ and ‘crunchy’ hoses. Did not replace the whole exhaust system. Had the car checked out (hopefully thoroughly) and the mechanic says it’s in good working order and should last another five years no problem. I hope he’s right. The joker who gutted the cat actually has a good recommendation on the Car Talk site and some other good reviews on line. I had a great mechanic in Tucson but I don’t live there anymore. Sigh. Maybe I should change professions.
Wikipedia claims that a faulty O2 sensor can cause the exhaust to be too hot and melt stuff in the catalytic converter. This would make sense, since we drove for 500 or so miles with a bad O2 sensor (after a Honda dealer told us it wouldn’t do any damage). I guess the hose was a coincidence and the distributor a red herring. With any luck we’ll never know!
Based on the random stalling complaint I’m not sure you’re out of the woods yet.
You really should consider calling the Honda dealer and getting that ignition switch Recall performed if it has never been done previously. The symptom of a failing switch is random stalling and seeing as how this Recall is free of charge you should take advantage of it.
Other possible fuel system related potential causes could be a failing main relay or fuel pump.