Here's my story, 2000 si:
- Original cat threw P0420 at 120,000 mi, so I put on a new Magnaflow and new secondary NTK O2 sensor.
- Replacement Magnaflow cat threw P0420 at 130,000 mi so I got a new one under partial warranty and also replaced the primary O2 with NTK, and I replaced the front exhaust gaskets at the bottom of the headers. (magnaflow claims they tested the cat and it was fine but they gave me half off a new one).
- Replacement NTK primary O2 dies at 136,000 mi (forget the code number) so I replaced it with a Bosch unit.
- Second replacement Magnaflow cat throws P0420 at 145,000 mi.

Ignition system is healthy
I do burn 1 qt oil every 2000 mi.
Exhaust tip is black, rear bumper isnt coated or anything.
Fuel filter has been changed on time.
I only run premium.
Mileage is at 31 hwy
Thermostat appears to be working fine and car warms up normally.

I'm thinking my oil burning is the issue on an already cheap magnaflow cat, I but wanted to see if any of you think I might be running rich and if there's any good ways to check this. I dont have a huge issue with spending $200 every 10,000 mi on magnaflow cats because I can easily swap them out myself, but it is annoying and I'm going to be moving to a state that has inspections.

 

I don't see any reason to run premium... The engine is designed to run on regular.

 

I don't think burning 1qt every 2k is enough to ruin a cat that quick. 31mpg highway is what your car should be getting so I don't think you're running too rich either. It's normal for the exhaust tip to have black residue on it, as long as your not belching black smoke I don't think there's a real problem there.

I think you'd be better off going with an OEM cat, I know they're expensive but you will save money in the long run if you have to replace the magnaflow every year or so compared to 10 years with an OEM.

 

b16a2 engines are higher compression and prefer (require) premium. Even says so on the filler cap and in the manual.

After getting used to the higher flowing magnaflow I'm not sure I could go back to the OEM Man it made a huge difference.


I'm also thinking that my 8 minute commute back and forth to work every day is not doing the cat any good because it's not getting up to operating temperature long enough.

 

I had to get an emission inspection this week so I was forced to put on a new cat just so i could walk in without a P0420. Here are photos of the old cat.... what the heck could those white stripes be? They were not located up into the header. Assuming an exhaust leak?

I noticed that farther up the headers was clean, but it got darker closer to the cat.