Hey guys been a little bit since I've been on. I hope to install the new UIM soon...there will be pics. Anyways onto my problem. My Cat is making a rattling sound, mostly when it'* cold. This problem worries me because I am not sure if my car will pass inspection when it comes time. I talked to a guy at a local shop he told me he thought the problem was that the catalyst was loose or something but he had no idea how it would show up when they check emissions. I wouldn't mind replacing it to ensure my car would pass since I could put on a high flow cat and get a new downpipe too. I don't really have the money right now, but it would be an upgrade and ensure I would pass so I could come up with it. What do you guys think?

Jack the car up and kick and shake the cat. It might only be an external heat shield. If the catalyst inside is loose, you almost certainly WON'T pass emissions.

OK, so if it is not the heat shield then just go for the upgrade to a high flow?
EDIT: What kind do I need? I'm looking and there'* 2-way and 3-way and stuff. Also I know it should be 2 1/2 out but what should it be in? Keep in mind I will be upgrading my downpipe too since we will be that far, what size should the downpipe be...keep it the same, the new one will be mandrel bent.

I'd aim that way. How has your gas mileage been? Most time a cat goes it'* cause the O2 had failed during and killed it by drowning it in fuel.

I put a new premium OBD2 cat on...not high flow... but I gained a ton of power from removing the restriction of the loose parts in my dead cat blocking the outlet.

My O2 sensor is most definitely bad, over 100k on the car and I am pretty sure it'* original. I will be replacing it soon. I figured that the O2 might be killing my cat...I should probably replace the cat.

Just because it'* old doesn't mean it'* bad.

But if you are getting poor mileage and your cat just died..then most likely it'* history too. Make sure you put in the O2 at the same time or before the new cat...otherwise it'll murder cat number 2

My gas mileage isn't horrible but I don't think it'* as good as it should be. I figure with the age I should replace the sensor anyways, it'* not that expensive. I'm pretty sure my cat is shot but I will check.

My 97 SSEi is original. I get unbelievable mpg. Although willwren will tell you I don't.

How could I tell if it'* causing problems? I just figured I'd replace it as a precautionary measure since it'* not that expensive. I average 24-26 mpg according to the pump, but most of my miles are highway so I think it should be better. Also as I mentioned once the car warms up it doesn't rattle nearly as much, any ideas why? That'* what makes me think it'* not the heat shield.

This sounds like a classic heat shield. When cold the welds are furthest apart from shield to cat. Once it warms up the expansion closes the gap and the noise goes away.

time to crawl under and check it out. Definatley before changing it out.

If the shield is loose...cruise over (in a different car if possible) to Home Depot..Lowes...whatever and looking throught the different areas..find the largest screw type clamp that you can. (Like the replacements everyone uses for heater hoses). If you need two..to get all the way around...pick them up. connect them together if necessary and tighten on the middle of your cat. Magically just fixed it and kept the necessary shielding in place.

Of course if you have a welder handy...just drop a little bead on it.