Signs of a failing cat, FiST specific?

[Clint Beastwood]

I had a bad EVAP issue, as in 18mpg on the freeway, gas smell all the time, tons of gas in my oil, etc. I was also getting a strong oil burning smell inside my car. The indications were, excessive fuel flowing into the oil was causing my oil level to be way too high, resulting in a lot of oil being burned. Now that the evap issue is fixed, I get ~24 city (up from 18 highway), and no more "dying at idle" after fueling up. It's a net positive, no more burning oil smell, but still "overly strong" exhaust smell, and exhaust smell in the car. I then tightened up my rear hatch significantly after marking the gasket with silicone grease, closing it, and finding out it wasn't making 100% contact. It's now making 100% contact, so the in cabin exhaust smell is reduced, but it's still a pretty strong exhaust smell, much more than I remember when it was new.

The reasons I think I might have cat issues:

1. I'm stock/untuned, back to stock exhaust, stock downpipe. My exhaust smells really strong (like, even after 3-4 hours on the road, it smells like it does during cold-start.)
2. The last couple mornings, when coasting to a stop I noticed a faint rotten-eggs smell, which historically = bad cat. Unable to absolutely verify it was my car, though.
3. As the weeks go on, my exhaust is getting more and more "poppy". Stock exhaust, but its sometimes popping alarmingly loud, and while inching along in traffic, not downshifting or compression braking.
4. That cat must have been taking a beating, since I was getting 18mpg highway. All that unburned fuel had to be going somewhere, and I can't imagine it did nice things to the cat.

The reasons why I am not sure:

1. I can't hook up my access port to check codes, so I bought an OBD2 reader. No codes stored.
2. At idle, the exhaust smells fine.
3. The car is running great, not at all like it's got a clogged cat.
4. No chunks of catalyst fell out (usually a strong sign something is amiss).

Anyone familiar with some FiST specific behaviors for a failing cat? When I get a chance I'll hook up my FLIR camera and pull some temp readings off the cat, not sure what else to check. It fails the smell test, but passes OBD2 checks and the "runs totally fine" tests.
I'd go to the dealer, but I'm kinda burned out on them telling me theres nothing wrong (then I wind up going home and fixing it myself, like my trans being "fine", but they only put 1.5l fluid in it).

 

[Se7eN]

could be residue from all that fuel it was burning when the EVAP system was having a fit

 

[PunkST]

Sounds like my car, lol. Sometimes it sounds like a gunshot, lol. Also stock cat with 103k. Was stage 3 currently on stock tune till im sure its running what id consider normal for it after the crash. I do have a catless DP ready to go incase it is actually fragged.

I wonder if the free flowing nature of the downpipe makes it harder to diagnose.

 

[Clint Beastwood]

could be residue from all that fuel it was burning when the EVAP system was having a fit

maybe - it’s been about 5k miles now so I thought it would have burned off. The intermittent rotten eggs smell is honestly what pushed me towards a failing cat. It’s much harder to pull this cat off and inspect vs previous cars so I don’t really want to have to do that

 

[PunkST]

. It’s much harder to pull this cat off and inspect vs previous cars so I don’t really want to have to do that

Thats for sure. Lol

 

[Erick_V]

When my stock cat failed I had an MBRP CBE (the loudest CBE) and a crackle tune. It kept going back and forth between normal loud to stock quiet for about a week before I blew the cat out. The car was permanently louder and I was told I was shooting flames lol. As expected I threw the P0420 shortly after, but Texas, so it didn’t really matter. It didn’t feel like the cat was clogged either. It felt just fine, no reduction in performance. I do remember more smell coming from the exhaust when I pulled into the garage and got out though.

 

[Clint Beastwood]

When my stock cat failed I had an MBRP CBE (the loudest CBE) and a crackle tune. It kept going back and forth between normal loud to stock quiet for about a week before I blew the cat out. The car was permanently louder and I was told I was shooting flames lol. As expected I threw the P0420 shortly after, but Texas, so it didn’t really matter. It didn’t feel like the cat was clogged either. It felt just fine, no reduction in performance. I do remember more smell coming from the exhaust when I pulled into the garage and got out though.

Any additional in-cabin smell, or just when the exhaust was confined around you?

 

[DoomsdayMelody]

I almost feel like you need to get it hot. Like take the car out and drive it like you stole it for 3-4 hours. Get heat soak issues, really make sure you give the cat an opportunity to cook off whatever might be on it...


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[scooter123]

IIRC the FiST has TWO O2 sensors, one before the CAT and one after the CAT. In addition to more accurate engine control capabilities having two O2 sensors can act to diagnose problems with the CAT. Based on your lack of any code I expect that your CAT is functioning within specification. Note, that does NOT rule out the possibility of a cracked convertor core but as long as you aren't throwing a code I wouldn't get too worked over it. Unless your car is aging out of the warranty period for the Emissions system, in that case I would push for a warranty replacement.

 

[Clint Beastwood]

IIRC the FiST has TWO O2 sensors, one before the CAT and one after the CAT. In addition to more accurate engine control capabilities having two O2 sensors can act to diagnose problems with the CAT. Based on your lack of any code I expect that your CAT is functioning within specification. Note, that does NOT rule out the possibility of a cracked convertor core but as long as you aren't throwing a code I wouldn't get too worked over it. Unless your car is aging out of the warranty period for the Emissions system, in that case I would push for a warranty replacement.

Nah I'm well within emissions warranty, ~25k miles.

It's just the constant exhaust smell/rotten eggs. If I could legally buy a whoosh catted downpipe I would in a heartbeat but even a catted downpipe isn't CARB approved and having been on the receiving end of an EPA violation, I don't want to do that again.

 

[Erick_V]

Any additional in-cabin smell, or just when the exhaust was confined around you?

Can’t say for sure. This was in the summer/spring time and I rode with my windows down all the time

 

[DoomsdayMelody]

Nah I'm well within emissions warranty, ~25k miles.

It's just the constant exhaust smell/rotten eggs. If I could legally buy a whoosh catted downpipe I would in a heartbeat but even a catted downpipe isn't CARB approved and having been on the receiving end of an EPA violation, I don't want to do that again.

I’d have a really hard time believing you could plug a cat in that mileage window unless you’ve been premixing your fuel with two stroke oil.


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[Sakel]

I've got a stock downpipe with cat for sale if you need a replacement

 

[Erick_V]

I’d have a really hard time believing you could plug a cat in that mileage window unless you’ve been premixing your fuel with two stroke oil.


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Not unlikely. My cat failed/was ejected out the tailpipe with less than <30k miles. If I wasn't FBO/Tuned I would have gotten it warrantied. But I live in Texas so it wasn't a big deal, for me at least

 

[Clint Beastwood]

I’d have a really hard time believing you could plug a cat in that mileage window unless you’ve been premixing your fuel with two stroke oil.


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well it was pushing so much fuel thru the system i was getting 18mpg highway.
almost 40 after they fixed the evap, and it was doing it for a looong time like 10k miles or so.

 

[TyphoonFiST]

Ill put money on it the Raw fuel did a number on the Cat.....document it now if its still under warranty to CYA!

 

[DoomsdayMelody]

well it was pushing so much fuel thru the system i was getting 18mpg highway.
almost 40 after they fixed the evap, and it was doing it for a looong time like 10k miles or so.

You dealt with 18mpg for 10000 miles????


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[Clint Beastwood]

You dealt with 18mpg for 10000 miles????


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Almost all of my driving is surface streets instead of highway (in the fist) so I hadn't really paid that much attention to it, but after i started getting gas in my oil i started going on long drives to test freeway-only mileage, built up a consistent set of data and went back to the dealership.

 

[Clint Beastwood]

I just watched the perps and Berbs videos - at present, with all the crackling and snarly popping and stuff - my stock exhaust is currently doing that. Coasting down in gear it gets a ton of pops and crackles - it didn’t previously do that which is weird. Sounds pretty cool though, but the exhaust sounds “wet”.

 

[PunkST]

Doing exhaust this weekend. I could shine a light into my cat and see whats up. Dunno what im expecting to see, but im not gonna pull it (the cat) unless im putting the catless on. Imo its probably failed on mine already.