[mpg_numbers_guy]

Good point on that. I didn't paint it for looks; there's streaks and uneven spots on the paint anyway, so if soaking it discolors it, then that's fine with me. Or it might serve as an excuse to add another layer of paint. Hopefully that won't be for a long time yet. Original catalytic lasted for 260,989 miles and 13 or 14 years. I just broke over 261k miles today - the highest mileage yet the most reliable vehicle I've been in that's over 10 years old!

Turns out that I'm missing just one part on the catalytic. Msjpiess pointed out to me on Insight Central that there is a support bracket that connects from the catalytic converter to the transmission housing to help support the catalytic. The one on my Insight was rusted out, and I wasn't aware of it's importance, so I just threw away what was left of it. Apparently it is a crucial part, and the welds on his catalytic broke without that support. So I ordered that part and it should be here next week. Part number is added to my previous post for complete reference.

Also something I learned today is that whenever a catalytic converter is replaced on an Insight (and probably most other cars as well), you should disconnect and reconnect the 12V battery to "reset" the ECU's settings with regards to air-fuel ratios and the like. My guess is that some things were adjusted to compensate for the exhaust leak that isn't there anymore. Drove it today, and lean burn worked well (in fact, between the warmer weather and no exhaust leak I was finally able to hold 150 MPG constant for over a mile for the first time ever on level ground without losing speed!), but the issue was that when the car went out of lean burn, it ran very rich. Driving that normally resulted in 75-80 MPG was 55-60 MPG. The car also felt as fast as it did with the IMA enabled...and it wasn't enabled. After I reset the 12V, I drove it around and the AFR and mileage returned to normal.