At 175,000 miles, my OBD2 bird was throwing 420 and 430 cat efficiency codes. In the interest of not buying new cats, I've been doing some research on a product called Cataclean. Anyone familiar with it? I'll share my experience with it so far.
I ponied up the $30 for a 16oz bottle and tried it, according to the directions. It successfully cleared the codes.
For 20 miles.
The light was back on, due to the same codes, so I did some hunting and finally found the MSDS for the stuff. It even lists the approximate percentages of the chemicals. So I bought some ingredients and made my own. I'm no chemist so I welcome any comments.
Petroleum distillates 5-10%
Homemade catacleaner cocktail:
Isopropyl alchohol 3.5oz (the 99% isopropyl stuff, not the 70%)
So far it's keeping the light off, but I only have a couple of tankfulls on record since clearing the code, so I don't have complete results on how well it's working. Due to the bird's transmission issues, I'm driving my OBD1 Mustang instead.