my 90 chevy has been noisy lately so today I see that there is a small about 1-1/4" dia plug that is on the bottom of the cat that is loose rusted and rattling.
Why is there such a plug on a catalytic converter?
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if the time ever comes you can't see it, you can lay on your back and do it from underneath.
I don't have the answer but wait til you price a new one.
I needed a cat for my $1000 beater. I got a price of around $500 for a direct replacement cash and carry down to about $150 for a universal cut and weld unit.
I noticed the guy that goes to the swap meets and sells switches,lights tools rattle cans etc.(all new) sells universal cats for $40.
I took one of those out one time, and found the large flat style Chevy/GM were full of ceramic beads instead of the honeycomb. Made it easy to empty them out and they still looked intact. Ah yes, back in my younger days!