Alright, I replaced my stock cat with a magnaflow high flow cat and I have a full exhaust (see reg). I replaced the stock one because it smelled like rotten eggs all the time and that means your cat is going out. So after putting on the high flow cat the smell went away... after about a month or so the smell is back but not all of the time. I've tried different brands of gas and it still doesn't work. It only does it when I run it hard. What do you think the problem is? I'm running 87 octane right now and nothing higher. I noticed if I use anything other than speedway or sunoco fuel the smell is significant. I tend to stay away from BP gas because it's not good for any car... This is really pissing me off. I know it can't be the cat because it's brand new. Any suggestions/comments welcome. Thanks!

what are your fuel trims? is your car running rich? is your front o2 working right?




1979 Impala Sport Coupe Aeroback

Actually, I think my o2 is the problem to my bad gas mileage right now and the smell... When I put the header on I made an extension for the stock o2 so I could reach the bung on the header. I think that extension is starting to wear out and it isn't working properly... It was only supposed to be a temporary thing until I got a new one but I still haven't gotten around to that... I should go buy a new one now knowing more things are going wrong. I think auto stores have them or shops.... What do you think?

if their is a leak at the bung your O2 will read this air and think it is coming from the exhaust stream. So you car will think it is lean, so it increased fuel trim and dumps more fuel. Or if you o2 is just warn out and cannot product voltage you would have the same effect. This will clog your cat.




1979 Impala Sport Coupe Aeroback

I went to Advance Auto and they have Bosch o2 sensors but they're the OEM replacements and are the same length. What would suggest for an o2 since the stock one or any replacement isn't long enough? I don't think there is one. I know Casper makes one but it's for running without a cat. This is annoying...