back pressure damage from clogged catalytic converter?

1989 Dodge B250 van, 318 cu.in. auto. I have noticed a big drop in power in the past few months, but it all came to a head this past week. Here's the scenerio: Driving down
the Interstate, cruise on, about 65 mph, when the engine suddenly gave a whoosh sound, lost power, started missing, and black smoke pouring out the exhaust. I managed to limp off at the next exit at about 30 miles per hour, found a garage and get it looked at. The engine analyser showed 'bad O2 sensor', so had it replaced. The mechanic at the time mentioned if this didn't fix it then maybe the cat. converter was bad, as small dust and particles fell out when he removed the O2 sensor. I continued down the road, everything fine. Next trip out, the same thing, the whoosh sound, missing, smoke, etc. This time, I limped into a garage and explained the history of the problem and asked if there was any way the cat. converter could be cut out, and a straight pipe put in its place. This was done to temp. get me home, as they had no cat. converters or ability to get one. The smog line from the engine was also cut, and tack wleded to the side of the new straight pipe. Anyway, the cat. converter was in bad shape, once removed. The 'pack' has been 'worn' away at the inlet end, rounded down, lots of dust and small particles in the shell of the thing, plus the 'pack' had come loose and was floating around in there. Started the engine, lots of black smoke and particles came out, then cleared up after about 5 miles driving. The change in the power and engine 'feel' was amazing. Much more peppy, etc. Also, the last tank of gas that I burned, filled up just after the cat. removal, got me 9.2 mpg, instead of the normal 15.3 that I had been getting. All in all, the engine runs like a new one again. After I got home, I replaced the muffler, it was mushroomed and full of the same dust and particles. I recovered even more smooth running and power.
Now, my concerns and questions: This engine was obviously, to me, suffering from several months of restricted exhaust flow, back pressure and the resulting buildup of deposits inside the engine. The only difference I can find now is the valve chatter is somewhat louder when the engine is under a good load, climbing a hill, etc. From the drivers seat, I can't hear any normal idling chatter, but with the doghouse off, it is really noisy at idle, with some valve chatter. I plan to change the plugs, check the timing and distributor. I don't plan to put the cat. converter back, unless it requires it for the engine working properly.
My questions: What is the likely long term result of running this engine for say 500 miles in this condition of restricted exhaust outlet?
What is the chances that there is a lot of deposit buildup inside it?
What is the best way to clean these deposits out, if they are there?
What about the chatter under heavy load? Can not having the cat. converter in the exhaust system have changed the engine to the extent that I need a gas booster or to go to a higher octane level gas?
Any help or thoughts will be appreciated.
James
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Good questions, i have same problem of cat. guts colapsing and ending up in the mufler, mine was followed by a loud exhaust noise at about 1.5KRPM. So not sure what caused tha black smoke in your exhaust. i did drive mine for about 100Km withought realizing i had a problem, was on the highways aswell. my mechanic says that is it OK to drive it like this, the only problem is the emmissions and here in Canada i can get a ticket for not complying. i do want to fix it this weekend so i don't get any more problem from the backpressure and the debris. mine was ticking a bit aswell, but a good oil change and an old engine valvoline aditive reduced it to nothing. By the way that is an awful mpg, what engine you have? is it the 3.0 or 3.3? mine 3.0 is giving me 13l/100km in city and 10l/100km on highway.
do you know if i can use any cat and mufler as long as it fits? or does it have to be exact for this model? thanks ilia
James Champion wrote:

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