Catalytic Converter Fries

[JCelesia]

I got my 81 (2000, FI, of course) and the cat was clanking. The seller gave me the O'Reilly receipt and they honored the replacement- I was pleasantly surprised. I got the new version of the Magnaflow cat and had it installed. It did well on the smog, but after a month or so the new one is fried. Much of the car has been restored, so it is generally in great condition.

Here are my thoughts. Any help would really be appreciated.

1. FI mixture isn't right and is running too hot...but temp stays at 190 (except in stop and go) and the smog was fine. So I don't think this is it. Is it?

2. The previous owner had heard that it could be the muffler creating a back pressure. My muffler shop has always been thought of highly by all and doesn't think this is the issue at all. It doesn't really really make sense to me.

3. Of course, the passenger seat gets too much heat coming up and I'll take the advice of others and glue in some insulation. That said, I'm wondering if heat from around/outside the cat is what is heating it up. So I'm thinking I need some way to insulate it...probably not wrap it, due to condensation creating rust. Not sure.

4. This might be my ideal solution, but I plead for advice: The cat is welded on, but is there a way to do a bolt on, take it off except for smog inspection? I read here that they run clean without the cat and run better.

What do you folks think? Has anyone else had this problem?

Thanks so much.

[seabeelt]

What makes you think its fried? If it passed smog, there shouldn't be an issue??

[TStark]

What is your base timing?
Are both the centrifugal and vaccum advance operating?

Any one of these off will send too much HC to the cat and overcook it.

What indicates the fuel mixture is correct? The cat's temp is suggesting othrrwise.

No, the muffler is not the issue, as your shop suggests

no, the cat is cooking from the inside out, not outside in.

No. Your car will not run clean without the cat, in that condition.

[So Cal Mark]

outside temps aren't hurting the cat, gobs of unburned fuel is the issue

[JCelesia]

Thanks so much - it WAS fried and clanked and then clanked more until it blew chunks. I then replaced it only to have it start the clank again. It got louder as before and there it sits. I'll take the advice given and see how it goes!

I hope I can pay it forward soon.

[JCelesia]

This might help one or all of you. As I said, I bought the car with much of it restored but the cat appeared fried. I returned it to O'Reilly and 4 years after previous owner purchased it, the Magnaflow was still completely covered by the warranty.

In a month, it seemed to be rattling again. I went under the car and couldn't find anything loose and finally concluded the cat was going again, and fast since it sounded the same. Ideas were noted in my post above. It didn't make sense to me that the mixture or vac advance or timing were off.

***The good part is coming.

So, my friend has a '69 Porsche 911. He knows a highly skilled, honest, and knowledgeable Porsche guy that has done great things on his and my friend's old Porsche. I'm thinking "Bosch FI, so maybe." So I call John Holleran, now at Berkeley Motor Works in Albany (next to Berkeley). They work on German cars, but he said he would certainly take a look. He called me up and said all the numbers were perfect, including the cat and before and after the cat. The next revelatation made complete sense to me.

What he noticed is the long exhaust run that only has front and rear brackets. I noticed that too and think it wasn't exactly designed to have a cat in the middle. Anyway, he welded a bracket on in the middle and it came to $320 for all the diagnostics, work and parts. (Apparently he has done some really fine welding on his own car, according to my trustworthy friend.) No rattle and runs beautifully. So!! The previous "fried cat" was NOT a fried cat. It gotten shaken up so badly that it broke into pieces which dislodged and blocked the exhaust, leaving me (and my wife) waiting for a tow truck...on my birthday...on the way to hear blues in the park and meet friends...on our first outing in the Fiat. She has recovered and now it's time to regain the trust and head to Napa.

Anyway, I imagine this could be a problem for a lot of Spiders and I just wanted to plant the seed. I don't think many mechanics would have caught this and I suspect a Fiat mechanic might not have thought of this, since he/she would have been used to seeing it the way it is. I did get a couple of names from you folks, so I will keep them handy and have a bit more piece of mind when I don't want to tackle something.

Hope that helps someone. Now I can replace the clock "glass" with the new acrylic one from AutoRicambi and wear it with a smile.

Cheers.

[toyfiats]

Some of the vendors sell a generic bracket that is designed to mount between the cat and rear muffler to lend additional support for just the type of problem you encountered. However, I would love to see the actual welding work that was done to yours, as it is always nice to have other options and see the solutions others have come up with.

[vandor]

Originally the Spider had two springs to hold the weight of the cat, however some aftermarket cats do not have the brackets for the springs.

[RoyBatty]

Yup,
As Csaba said. My '75 had two tabs under the car on either side of the cat and the cat had a tab with a hole in the outer flange to take a support spring that would support the cat without allowing any rattles.
Once I removed the cat I noticed those tabs were great at stabbing you in various places as you worked under the car.