Catalytic converter ratteling When hot...

[DJsMX-3]

Hey all when i have driven around for a while and the cat gets real hot is starts to rattle,but only at certain RPM intervals..

It sounds just like if the heatshield was loose but is isnt,theres barely any rust anywhere on the cat (It looks allmost new)but it is 12years old i guess....

Has ANY ever experienced this??
The sound isnt like a little stone or something thats gotten in under the heatshield,but it is a metally resonating sound

Should i just replace the old thing?? I spent all last night reading old posts about cat/highflow cats... but didnt find anything..

If my only option is to replace it i want a highfow cat,but my searches only came up vith catco and magnaflow.

They dont seem to offer a direct fit bolt on,or im searching the wrong places..

Hope that some of some of you can help,maybe one of you hardcore technical guys

[perhapsadingo8yerbaby]

I had a similar problem on a 95 RS that took a while to figure out. Maybe your GS has a similar set-up. My Cat heat shield seemed solid even when the unit was hot but the rattle persisted & got worse. I checked it many times before figuring out that there were two Cat heat shields-one on TOP as well as underneath the cat converter. The bottom one was tight but the top one was doing the rattling....

[DJsMX-3]

The heatshield fully encloses the cat all the way around... unless im missunderstanding you and you mean that theres another heatshield under the exterior one??

[perhapsadingo8yerbaby]

Yeah, I didn't explain that real well. In my case, the heat shield I was referring to was mounted over the cat but actually attached to the car's underbody (I think). I found it by tapping on/around the cat & exhaust sys with a wrench handle while the unit was hot. That's how I narrowed the location and figured out the likely problem.

Vowed to put the car up on ramps & fix it asap when that weekend, the damn thing came completely loose on a highwayspeed night-run to the beach. Fortunately no other traffic was around because it came flying off the car like a metal frisbee and went sailing. I went back to find it but never did... Hope that helps somewhat.

<small>[ June 21, 2004, 02:57 PM: Message edited by: perhapsadingo8yerbaby ]</small>

[TekPmp]

I have the same problem in my hollowed out cat. sounds like theres marbles inside. I thought maybe there was some left over "honey comb" inside but I never thought to check the heatshield. As with you, mine only rattles when hot

[Jin-Roh]

I have the same annoying sound coming from somewhere under the hood.

It only happens when the vehicle moves and accelerates but it's not RPM depending! It does not happen when the car doesn't move.

So far I had some very different input from Mazda services what it could be: bad gaskets, ruined engine, loose heat shield…but they can't locate the noise and the fault.

I hope it's just the headshield around the cat…

[ChrisG3]

On most loose cat shields, I used a larger hose clamp, get it pretty tight and bend the excess metal of the hose clamp over the screw to prevent it from backing out as quickly. However, I have seen where the heat shield on the body rattles. Which, if that is the case, find some self-tapping sheet metal screws and have some "fun" putting them in. You might want to make a SMALL pilot hole with a drill first, due to the occasional PIA factor of getting self-tapping screws into the body. NOTE: You might even want to use some modified fender washers (holes enlargened) with the self-tapping sheet metal screws to put more pressure on the body heat shield.


Chris

[MX#3]

i have same but mine does it when it is cold or hot when ever rpm around 1500

[ikarus1]

usually the welds just break on the top shield - have someone at a exhaust shop hit it with a mig and she'll be as good as new....

[DJsMX-3]

Perhaps:It isnt the heatshield over the cat,i dont even think theres a underbody heatshield before the pre-silencer,cant remember right now...

I know the sound is comming from the cat itself because i had one of my girlfriends sitting in the car flipping the throttle while i was under the car listening around..Should have had a see-thru bottom Eh?

Jlove: im still a bit confused when you guys talk about top/bottom part of the heatshield Because mine cat has one heatshield wrapped all around the cat..offcourse its out of two pieces but theyre folded together all the way around it,Is it just the tophalf of the two you mean??
Apparently theyre pretty good stuck together as they should be..

ChrisG3: If i put a large hose clamp around the cat and the sound went away i would defenitly know that its the outer heatshield thats doing the rattling and nothing inside,but it wouldent be a durable solution would it??

And if its still rattling i would know its inside,or dosent the hoseclamp allways apply enough pressure to keep the shield in its place?

If it teases me much more im just gonna replace it,does any of you know of a good direct fit bolt on High-flow cat? something that wont slow down the exhaustflow from my K8,but then again it shouldent be to restrictive,so that it would work if i get a KLZE some day
OH and what about the sound of a High flow cat?? will it change the sound of my system much??

[perhapsadingo8yerbaby]

Sorry I can't be more help without seeing it at this point. Guess it is possible that the rattle could be coming from a loose element inside the cat but I'm still leaning toward an external cause simply because that is so much more common. Still, a new cat can be fairly pricey so I'd want to be as sure as possible before buying the new one. I think others here would be more qualified than me to recommend a hi-flo replacement.

Let's see, you're in Denmark. I was there once in Copenhagen and enjoyed it VERY much. hmmm... put that "see-thru" panel you mentioned into the floor and one of your "girlfriends inside flipping the throttle" and I'll bet any number of ppl on this board would offer to fly over and fix it FOR you... I would if my wife would give me permission yeah RIGHT, like THAT's gonna happen. Ok, that was probably in poor taste but you started it so I'll leave it there.

[DJsMX-3]

Perhaps: Dont think people would bother flying to Denmark to see "throttleflipping" Over here a OLD very bad joke is/was that some "people" you dont like should have a see thru bottom in their cars. "Uhmm theres something with Americans thinking that the French are snobby right?" SO joke could be translated to: Why does the French have see thru bottom in their cars? So they can see whom they run over...

I KNOW its bad but thats actualy whats supposed to make it funny

But thanks for your help so far Perhaps...

[ikarus1]

You can try the hoseclamp solution to see if that quiets it down, if it does, then you need to have the shield re-welded. Thermotec even makes stuff you can wrap around the cat like header wrap. I would probably just replace it though with a Carsound or Catco hi-flow converter, but you might want to go up a step in size if you are every going to do a performance exhaust....

[DJsMX-3]

Jlove: I have been looking at carsound(Magnaflow) but it dosent say anywhere that their direct fit bolt on cat is High-flow,maybe it is,but i have read around and couldent see it anywhere

[DJsMX-3]

So anyone know of a good wellknown brandname of Highflow catalytic converters that offers a direct fit bolt on for a MX-3 1992Gs??

And allthough theyre Highflow they still do their job right so i will pass emissions test right??