Diminishing performance

Well, this catalytic converter is being very difficult. The flange connection at the exhaust end of the catalytic converter serves to connect the pipe and muffler (which is off the car) to the catalytic converter and the catalytic converter to a rather substantial hanger complete with cushioned mounts. One of the two bolts holding the catalytic converter to the hanger finally came loose using an air gun and socket, the other has not budged after repeated tries and soaking with penetrating oil. The front appears to be held in with an exhaust clamp which was placed with the nuts on top making it very difficult to break them loose or even to saturate with penetrating oil. Space is very limited and I cannot get anything long in there to help me apply torque to the socket and ratchet. I have tried tapping it but space is too limited to get a good swing with even a small hammer. I am thinking of just cutting it off if I can get my tool in close enough with an abrasive wheel without damaging everything in its vicinity. There is stainless steel tubing to both the cat and the transmission very nearby. Why a flange with adequate room for access was not used on that end is beyond any reasonable logic.

There is a lot of soot in the pipe on the exhaust side of the catalytic converter. The interior looks good but I noticed almost exactly half (right down the middle) of the material inside appears be sootier than the other half. When I rev the engine I see smoke billowing out the back; something the car has never done up to now.

And so it goes.

88

Hi guys!

First, thanks very much for your enlightened suggestions they have led me to solving the problem. I am glad I took the time to keep investigating and talking to you guys before jumping in. It saved me a lot of money and labor.

It turned out to be a plugged catalytic converter, as you suggested. The car runs much better after testing it without the exhaust and blowing out the built up carbon. All the previous problems we discussed, the high speed idle, the dieseling, lack of performance are all gone. Now I need to replace the muffler and the catalytic converter.

Just for information for anyone else reading this string, the three way catalytic converter I have on my V8 has three chambers separated by screen. The first chamber (entry chamber) was crumbled. After getting it off I shook it and heard the pieces and dust rattling around and poured them out. Unfortunately, I was unable to detect this while still on the car (like by tapping). Taking it off was a chore as one of the rear hanger bolts was quite seized, but perseverance with an impact wrench (and lots of heavy duty penetrating oil, tapping, and a little heating and any other trick you know) finally, after several hours, did the trick. The intake side was held on with an ordinary u-clamp which I finally had to cut off (I got sick of playing with it by that time and decided my time was worth more than the price of a new u-clamp). I also had to cut length ways along the short stainless sleeve on the air tube to free up the air injection tube on the side of the catalytic converter. Go slow and take it easy so as not to cut into the stainless tube (I cut mine a little but it can be easily fixed by using a slightly longer sleeve) that carries the air from the air pump (if you have one) and peel it away along the cut so the tube on the cat slips easily out as you pull the cat loose from the pipe coming from the manifolds (the intake side) which is not easy on an old car (mine has 120, 00 miles on the original equipment). But, again. A little tapping (do not dent it or it will be harder to slip off), penetrating oil and shifting back and forth and up and down finally got it loose.

So, that is my story and I am sticking to it! Any knowledge about where to get a 23 1/2" end to end (including exhaust end flange) three way catalytic converter as good as the original will be wholeheartedly appreciated (I know good luck, right?). Apparently, GM does not supply them anymore.

One last thing. I read the spec's on the Aero Turbine muffler 2525XL and wondered if it is a good choice. It is all stainless steel and comes with a lifetime warranty. Supposedly, it has no baffles for low back pressure and uses wave cancellation to quiet the exhaust pulses. Aeros are primarily for diesels, by what I have read, but this one looks like it should work fine on my V8 unless it is too loud (it is a luxury model so I do not want it sounding like a hot rod). The XL is supposed to be a quieter version of the 2525.

Thanks,
88

Thanks, Saturn. I checked out the site. It is one I have seen before in my search for parts. They seem to have a good selection. And thank you, Steve. I have checked out that Walker with the lifetime warranty and it is certainly a contender.

Just a note on my last comment. The sections are not separated by screen. It looks like screen in the front and back with the limited visual peering through the hole but it is the honeycomb upon further inspection.

Thanks again.
88

That is very generous of you, Saturn. My thanks, once again.

88

Just another quick question if I might. This car is now running almost perfectly now that the exhaust restriction is gone. However, when I put my foot into it I cannot always hear the secondaries honking. If it kicks down into first gear I think I can hear them. I understand they are governed by the computer which decides if the engine needs more air for proper combustion (Rochester quadrajet). Also, there is frequently a slight stutter sometimes when taking off from a complete stop.

Thanks,
88

That makes sense, but I can see/hear/smell gas squirt when I activate the throttle with the engine off.

88

Any thoughts on the secondaries?
88.

Thank you, Saturn. Yes I have read about them and there are mixed feelings about the design. Some dislike them, others say these later ones are okay. Mine is the original, untouched, so it may very well be ready for a rebuild or at least new gaskets, but overall it runs pretty good and gas mileage, now that the exhaust is not clogged, also seems to have noticeably improved. Soon as the gas prices come down again, I will fill it up and check the mileage more accurately.

If it is any help, I have noticed (because I am listening more closely now) that the secondaries may be opening mid way through a full throttle acceleration, if that is any clue. Maybe it is designed that way since fuel economy was a driving force in those years. Anyway, it is no big deal if the gas mileage is good. I am not racing it and it has plenty of pick up for passing. I just thought you might know a couple of easy tweaks for best performance.

Thanks again and Best wishes,
88.