Re: 9020V Catalytic Converter Noise

[steveb@falcon.kla.com (Steven Buchholz)]

> I've been hearing this raspy noise sounding like a loose heat shield
> coming from my exhaust system for a while and decided to look at it this
> weekend. Turns out that it seems to coming from inside the catalytic
> converter and can even be heard at idle if you are outside the car.
> Also, if you hit the side of the converter with your hand with the
> engine not running, you can hear what seems to be something loose in
> there.
> 
> Anybody ever seen anything like this before? Does it mean I need a new
> converter? Seems strange because the car only has 40K miles on it.
> 
... I've said it before and I'll say it again ... check to make sure the
weld that attaches the heat shield to the body of the cat has not broken.
I have personal experience with the older cats from the late '70s and if
the car was from that period I'd wholeheartedly agree ... but the newer 
ones are much more robust; I'm sure that some have failed at 40k, but 
probably not many.  As someone else pointed out you might want to take 
the car in to see if you can get it handled under warranty ... at some
point the warranty was mandated to be 100k miles.  

If you want to do a quick check for the heat shield let the exhaust system
cool off and try moving the shield fore and aft on the cat ... if it moves 
even a fraction of an inch it is likely to be the culprit.  If this is your 
problem you can have it tacked back on if you'd like, but my solution was 
to find a hose clamp that fits around the front neck of the cat, behind 
the mounting flange.  Cinching down the hose clamp forces the front of the 
heat shield against the front of the converter ... stopping the rattle.  
My brother-in-law thought that he was going to have to buy a new cat, but 
I made a believer of him now too ...

HTH!
Steve Buchholz
s_buchho@kla.com
San Jose, CA (USA)

Funny enough I had my own cat-related experience over the weekend ... I 
took my '78 Audi Fox out for a spin after a long stint in the garage.  
When I got to my little fun stretch of road I noticed that I was experi-
encing a power loss, and I started to hear a hissing sound coming from 
under the car.  I didn't want to have to leave it by the side of the 
road, so I turned around and limped home.  By the time I made it there 
I could barely climb the hill leading to the house, and the engine could 
hardly idle.  The hissing noise was exhaust gasses escaping from the slip 
joint between the downpipe and the cat ... guess I'll be getting a new 
cat before I take the car in to get smogged!  I'll have to run that tank 
of gas out first ...