I jacked my car up, went under, checked all connections, tight as hell, if I bang my hand against the I-pipe or cat, there is a loud rattle from inside the cat. Does that means the honeycomb inside is falling apart? My exhaust smells terrible, not like fuel...but just stinks...burns my nose.

 

when I first bought my car there was this rattling sound, I couldn't find it until I needed some exaust replaced...sure enough the muffler shop guy says the cat is bad. then the muffler guy says he will just put in a straight pipe for less than the cost of a new cat; guess what I had done

 

DO NOT INHALE that crap!!!!! Your honeycomb is smashing around in the turbulant exhaust. I cracked mine due to a backfire. It was gone in less than a week.

 

I have to go through the sniffer in 2 months....so I guess I'll need to get a new cat put on. So the rattling that I hear from inside the cat is indeed the honeycomb falling apart. Is that hurting my exhaust flow?

My exhaust reeks....I don't make it a habit of inhaling exhaust fumes....but the smell is terrible and caught me off guard when I got a whiff.

 

If its rattling around after you bang on it and the exhaust smells - like rotten eggs, your cat is toast. Happened to me. While it was bouncing around, it somehow wedged itself into the cat outlet and restricted the exhaust flow to the point of making my Z28 undriveable.

 

Yep, same thing happened to me. Got new engine installed, fired up and then heard this rattling noise. Jacked it up and hit the convertor, there it was. Replace old cat with a Hi-Flow cat. If you don't have it yet, now might be a good time to also add a nice cat-back system too.
Also, if you are planning on doing the AIR pump delete, then you can just get the cat w/o the extra air line coming off of it. (That line gets capped off after AIR pump is deleted, anyway)
Are you going to be doing the work yourself?

 

This happened to me last summer. I had a guy put 2 staight pipes in place of my 2 cats. But now I have to replace the bad one and put the old,good one back on. Has anyone replaced cats on a dual-cat car before? If so, what did you use?

StealthElephant: be sure to replace ur O2 sensor cuz that may be bad, maybe even have the computer diagnosed to check for codes.

 

Yes - had to get my dual cats replaced, the first time, I had the shop lower my Y-pipe and cut off the old bad cats and installed/welded on new Random Technologies direct fit replacements. Pretty costly - $400 for the 2 cats + labor. Go figure - I had a bad O2 sensor - caused one of the Random cats to go bad. Well this time I'm going to replace my original Y-pipe with a brand new 2 1/2" mandrel bent Y-pipe from Carsound and it has 2 high flow carsound cats (9400 series) part # 23479. Here is the url:

Carsound cat and Y-pipe

I haven't installed it yet, but laid it out under the car - one thing there is a difference in how the Y-pipe will fit the catback - no "hog clamp" - its a slip fit. Nothing a good shop can't make work.

Its stainless and 2 1/2" all the way, not 2 1/4" in sections like OEM.

Oh yeah - cost $ 363 delivered to VA.

 

I used the CATCO universal with A.I.R. fittings hi-flow cats, got them off e-Bay for like $40 each plus minimal shipping when I had to replace the dual cats on my 91 Firebird last month.

 

That was my intention too. I was just worried about the bends right out of the original converters, wasn't sure if they would ft right.
Now I feel better. What inlet size Catco converter fit our cars?

 

Stock sized Y pipe is 2.25"

 

thanks for the info. I'm sure you've heard this alot, but ur formula is awesome. I've never driven a standard shift f-body yet. hopefully someday

 

Thanks for the compliment!