For those of you who are replacing cat converters, try to look at a new one and then look at your old one. A cat insides look like a Kit- Kat candy bar, a real fine honeycomb. The job of this device is to burn up HC & CO that gets by the combustion chamber. With PROPER engine management these are very small. However, when you have excessive blowby, or a fowled plug, or a aftermarket chip that dumps more fuel than the engine can use, the cat is forced to burn this excess coming down the pipe. When the cat is overwhelmed, it melts and/or breaks up. When I pulled the exhaust off "that Baltimore piece", it had a cat that was about 2 months old. It was melted slag inside. For those of you who followed my post on that car remember that the previous owner had not a clue to what preventive maintenance was. The engine really suffered from neglect and blowby was only one of its ails. One the other hand, I pulled a factory cat of a 87 Buick with 150,000 miles and it "looked" great. I would be hesitent to use it for I feel that, even under ideal conditions, a cat's efficiency when you've pushed 100,000 miles of exhaust thru it, is less than ideal.
BTW, the replacement cats available today are about half the size as the origional. Hi-Gear sells them (in your hand) for $69. The same one I've been getting from NAPA for $120!
From: Tin Man
OK, this did NOT work for me but the Helms manual says you can check the Cat by using a vacuum/pressure gauge. Attach the gauge at the O2 sensor mounting location using an adapter. The pressure at idle should be less the 1.25 PSI. Now slowly increase the RPM's to 2000 RPM's. The pressure should not exceed 3 PSI. If you measure more than this, your exhaust system has some obstruction. You may need a new cat.
From: Lee Brown