back pressure damage from clogged catalytic converter?

I posted this to alt.autos.dodge this morning, and got no response, so thought I'd try it here....
1989 Dodge B250 van, 318 cu.in., auto. 188,000 miles.....
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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Hrl
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On Sat, 01 Jul 2006 20:54:22 GMT, Hrl
Unless you overheated the motor doing this , the chance of any real damage to it is light. You did stop it and take action when it got bad which may have saved your engine. I would change oil and put in some fresh oil and as far as lifter tick, given the miles on engine, I would not worry much about it unless it starts getting worse. ----------------- The SnoMan www.thesnoman.com
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Thanks, I appreciate your thoughts....
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wrote:

Some of the crap may now be clogging the muffler. Take it off and see what falls out when you hold the inlet down and shake it. On my car it looked like all the stuff out of the converter was in the muffler.
Al
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Yes, it did. I replaced the muffler last week and the old one was mushroomed out, had lots of dust and pellets/particles in it.. It's amazing the amount of junk that came from one screwed up converter...
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Hrl wrote:

In theory, a clogged cat will put so much pressure back into the heads that the exhasut valves can carbon up, burn, or even melt. In theory. If the engine seems to run good, ignore it. You could try putting some Sea Foam or marvel mystery oil in the gas tank, but I don't think it will change much. That engine will take an incredible amount of abuse and still keep running.
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On Sun, 02 Jul 2006 00:10:58 -0600, ".boB"

Thanks for the reply. That is reassuring.....Have you ever poured Marvel Mystery oil, or similar down the carb on a vehicle to clean things out? Any experience with the various brands of 'engine restorer"?
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Hrl wrote:

I've put MMO in the fuel tank as a carb cleaner. That seemed to work OK. I also use B-12 Chemtool as a carb and injector cleaner. I do that every so often, usually when I'm in the parts store and I happen to think about. I put a fair amount of miles on my vehicles, use cheap gas, and I never seem to have any trouble with clogged jets or injectors. I've used Restore on a number of vehicles over the years. It does seem to help. Cut's down on oil burning anyway. Years back I tried a product called Matrix. Very expensive, and there was more to it than just dumping it into the crank case. Didn't do a thing; huge waste of time and money. About 15 years ago I had a '69 Mustang with a 351W engine. On cold startup (esp in the winter) the valves would really clatter for about 30 sec, and then fade away. I put in a can of Slick 50, and the valve clatter went away. Didn't do anything else, though. No change in performance, still burned the same amount of oil, no change in fuel mileage. 5 years later I rebuilt the engine and it was pretty clean inside. That's my story, and I'm sticking to it ;)
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On Sun, 02 Jul 2006 00:10:58 -0600, ".boB"

I question your theory. The biggest danger here is engine over heating and damamgeing headgasket and other engine parts, not burning exhaust valves. ----------------- The SnoMan www.thesnoman.com
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wrote:

that the

And, ruining the EGR valve. They get very hot when the converter plugs. On my vehicle I was lucky, the converter plugged so tight the engine just quit.
Al
Al
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I'm suprised a mechanic removed the cat, IT is very illegal to remove it. NOT haveing it can screw up the O2 sensor readings
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On Mon, 03 Jul 2006 03:16:53 -0400, "sqdancerLynn"

That's why I didn't use location details, being under the table, emergency, 'gotta get home' work, with a wink , a nudge, and cash money...:)
How does not having it screw up the O2 sensor- specifically---fule mixture, idle speed, timing, advance? I wondered what, if any effect that would have. Although now is so much better than then....
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It doesn't.... it will only affect an OBD-II-equipped vehicle, with a post-cat O2 sensor. And even at that, all it will do is light up the Check Engine light, due to the post-O2 sensor being out of whack. However, the post-cat O2 sensor has nothing to do with fuel injection control - it's just an emissions cop.
You're pre-OBD-II vehicle will have no issue running without a cat - except maybe for a decrease in peak torque because of lower-than-designed backpressure in the exhaust system. Stick a half of a potato in the exhaust pipe to compensate :^)
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On Sat, 01 Jul 2006 20:54:22 GMT, Hãrõlð

First things first - about the "valve chatter" under load. If it is under load, more likely than not you have spark knock, or ping. Try a tank of PREMIUM fuel and see if it is better. If so, you need to find out why/ If your EGR is not working, that could be part of it. Or you could have a good dose of carbon in the cyls. If the premium does not solve it, it MAY be valve lifters. Change the oil. Put in10W30 or 10W40 with one quart of "marvel mystery oil" and see if it gets better in about half an hour of driving. If the premium makes it better, put a can of fuel injector cleaner in the tank and/or get a can of combustion chamber cleaner (your GM dealer will have it, your chrysler dealer should.)Follow the instructions on the can.
The lack of the converter will NOT cause an engine to require higher octane fuel, but a 318 with 188,000 on it may very well like mid premium.

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On Mon, 03 Jul 2006 22:04:59 -0400, clare at snyder.on.ca wrote:

I haven't tried the premium fuel yet, and just yesterday bought sparkplugs, pcv valve, oil filter and oil, air filter, a can of Mystery oil for the crankcase and maybe down the intake, a can of premium Gumout fuel and engine cleaner. Gonna do all that tomorrow or Thurs. and will report back with the results. Thanks for the ideas....and the reassurance...lol
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