[BigV]

hm.

I'll tell you what I know about catalytic converters, Clodfobble. See if there's something there for you...

The catalytic converter is aptly named, it uses a catalyst, notably platinum, to convert substances in the exhaust stream to less toxic substances. The platinum, and other magical chemical stuffs, aren't consumed by this process, just used like eeensy weeensy chemical tools to rearrange the compounds flowing past. Mechanically, a catalytic converter works like this: take a double handful of drink stirrers, the hollow kind, and wrap your fingers and thumbs around a large bundle. Now, pick up the bundle and look through it. Weird, huh? It's like a straw of ten thousand tubes. Your catalytic converter is like this, but with tinier holes, and lots more of them. The surface of the straws are coated with this catalytic compound. The whole thing looks like a brick, except along the axis of the "straws", through which the exhaust flows. This "brick-thing" is contained in a kind of can with the exhaust pipe running in one end, through the cat, and out the other end.

When the exhaust gasses heat up the cat to the normal running temp, the chemistry does its magic, making the exhaust less toxic. That's when things are running right. But, naturally, things can go wrong. There are a couple MAIN ways a catalytic converter can fail.

It can be ruined chemically. One easy (well, used to be easy, now it's harder, but you get the idea) way is to run a tank of leaded fuel through the car. The car will probably be ok, but it will poison the catalytic converter. It's a goner. The lead ruins the surface so the chemistry doesn't happen. The car will run fine, but the emissions will be bad. There are other ways to degrade the cat too, if your car is burning a lot of oil, that can crap it up too. So, you can foul up the cat chemically (pun intended).

You can also ruin a catalytic converter mechanically. That "bundle of straws" I was telling you about? In the cat, they're made of ceramic, like your.. well, I don't know what it's like. but the upshot is the thing is FRAGILE. And it is impervious to heat, that is, you can't melt it, and "send it down the tailpipe". If it gets broken anywhere, even a little, it will crumble, maybe slowly, maybe all at once, and you will have a MECHANICAL obstruction to your exhaust flow. This, as you may well imagine, is bad. This is (probably) the "plugged up" scenario you heard. I can hear a failing catalytic converter, they have a distinctive tinkling sound at low speeds. That is from the ceramic element rattling around in the metal box that contains it. When they're new, they are neatly, and tightly fitted inside the box (it could be many different shapes, box, cylinder, tube, lozenge, etc, whatever). As the car is driven, and it gets shaken around, it's possilble that this ceramic honeycomb gets rattled around and maybe knocked loose a little. Imagine it's still in there, but knocked around some, so that the corners are rounded a little. Now it just sits in the can, which is fine, but it's a ceramic "brick" sitting in a sheet metal "can" attached to the exhaust plumbing. It's gonna rattle. That's what I can hear, you could hear it too.

Anyhow, the cat that comes with the car is designed specifically for that car in lots of ways. Like, where it connects, how hot it will get when the engine is running normally, how much flow it can accomodate, how much catalyzing surface area is available to the exhaust, etc etc etc. Your "universal" one isn't designed with these specific parameters in mind. It likely has the same chemistry setup, but will it be hot enough? too hot? too restrictive? too "loose"? etc etc etc. These are the kinds of unknowns that give the mechanic pause regarding the efficacy of the universal parts. I think the chance that the universal units would NOT WORK AT ALL is low. Unless they're like, mock ups or some other nonsense. I think you could just BYPASS the flippin converters all together and the car would still run, but you'd be passing untreated emissions. But the car would run.

Does this help?