Cats going bad?

[06YukonXL]

I recently acquired a unicorn. An extremely clean (so clean you could eat off of it) 2006 GMC Yukon XL with 108,000 original miles on it. One owner vehicle that an older man bought new. I noticed after driving for a few days and parking in the garage it smelled like rotten eggs. It doesn’t really run bad. Seems to have a decent amount of power. It has a slightly rough idle though. I sprayed brake cleaner around the intake (no change). I then removed the throttle body, cleaned it with throttle body cleaner until it looks new again, cleaned the MAF with mass air flow cleaner and left the battery unhooked the entire time. Did the idle release process and it didn’t seem to help.

A buddy of mine that’s a GM tech put his GM scan tool on it and confirmed the rear o2 was reading funky so it’s not getting good airflow through the cats. What’s my best course of action here? Everyone I’ve talked to is just saying cut the cats off and delete it or gut them out and delete it. I have a buddy who tunes LS powered cars for a living and said he could do it no problem. But, then I read horror stories about how they run like crap and fuel mileage takes a huge hit as well. Not only that, this is such a nice vehicle I don’t want to just cut the cats off off it. I checked the price of a new Y pipe through GM with both cats and the price was over $900

 

[06YukonXL]

I guess my biggest question is, will it hurt anything driving it like this until I save up to just buy a new Y pipe through GM? Other than a rough idle, it seems to run and drive perfectly fine. I’m thinking this thing probably never saw more than 2,000-2,500rpms it’s whole life and the cats just never really got “hot”.

 

[B-train]

Usually the rotten egg smell is from running rich. It may just need to be driven on a long highway run with fresh gas and some injector cleaner. Other possible causes are intake gaskets (you said you checked with brake clean, but try water and watch for white smoke out the exhaust). A MAF that isn't reading right, or some other vacuum leak that is causing the mixture to be off. The rough idle could be dirty injectors, a vacuum leak, or an engine sensor.

If you could look at live data while you drive and make sure the primary O2 sensors are going above and below 500 or .50 on their readings. If one is stuck below mid-point the engine will try and add more fuel. If it's stuck above the mid-point, then it will take fuel away and give a lean code.

 

[nonickatall]

there are two ways to fix this.

Remove the catalytic converter and clean it with a high-pressure cleaner. Of course, make sure that you don't apply too much pressure and destroy the structure.

You can also rinse the cat from behind with cleaning agent and water so that the dirt can come out of the fine pores. This way you can save a cat.

Otherwise, there are aftermarket Cats in the right size that you can weld in, they actually work well and don't cost a lot, but I would definitely exchange the cat, because the bad flowing exhaust, that the cat creates from the clogged cat is not good for the engine in the long run.

 

[swathdiver]

Whatever you do, do not use cheap Chicom cats as they will fail inside of a year. Cry once, buy once. I went with Magnaflow's Y-pipe and cats at the time as the OE stuff wasn't available then. No problems after 5 years.

 

[nonickatall]

Whatever you do, do not use cheap Chicom cats as they will fail inside of a year. Cry once, buy once. I went with Magnaflow's Y-pipe and cats at the time as the OE stuff wasn't available then. No problems after 5 years.

I wouldn't use the cheapest china stuff either, but I've welded in quite a few aftermarket cats and so far not a single one has failed. But if I see that the price from the original manufacturer is sometimes up to 2000 € and I can get an aftermarket cat for around 100 bucks, then I can weld in a lot of cats, even if they fail after a few years.

Don't get me wrong. If you have the money I would use an original cat, but better than to remove the cat completely, is to use an aftermarket cat, when you are are short of money.

But in the first step I would try to clean the cat, because mostly the problem is, that particles of dust from the soot clog the cat. So if you get to the cat element and see that it's still okay, you can try to clean it, which often leads to success.

If the cat of course already crumbled inside, you can forget that point, but that's an inexpensive method to do that all to save.

 

[Doubeleive]

i'll second the magnaflows and they should be slightly cheaper than a oem y pipe, prices were way up during covid but I haven't checked in a while, now it's inflation

 

[Alex_M]

I've used a lot of aftermarket converters, including half a dozen Magnaflow's. I've had both burn out, I've had both last. Roughly the same failure rate between them.

If you want to put in an aftermarket converter, I'd recommend just ordering some of these (link) and take them to a local muffler shop to have them welded in.

If you have "complicated" feelings about emissions like I do, or simply don't care, then I'd recommend having the converters removed and weld in resonators like these (link) that look a lot like a spun style catalytic converter. This will pass a visual inspection if you've got a cop in a bad mood.

Whatever you do, make sure you keep your factory cats. Find a scrapper that will pay you fair for them based on the numbers on them. You can wire brush and google the numbers to get a rough idea of the value. Lots of folks will try to under-pay to turn around and make a bigger profit.

Of course, all of this depends on your state and local's emissions practices. If you have to pass an emissions test, make sure you get a 48 or 50 state certified converter. Though, sounds like it's not an issue in your area.

And to answer the concerns listed - you will notice no difference in power or fuel mileage, unless your converters are impeding exhaust flow in which case you will notice an increase in power and fuel mileage. Driving around with clogged catalytic converters *will* damage your engine over time.

Last question - have you changed spark plugs? At that mileage, it's due if they haven't been done and could be the cause of your issues.

Ammendum: after actually getting the links, the price is the same now between the resonators and the converters. When I did mine the resonators were half the price of the converters. Use your own judgement.

 

[Doubeleive]

I've used a lot of aftermarket converters, including half a dozen Magnaflow's. I've had both burn out, I've had both last. Roughly the same failure rate between them.

If you want to put in an aftermarket converter, I'd recommend just ordering some of these (link) and take them to a local muffler shop to have them welded in.

If you have "complicated" feelings about emissions like I do, or simply don't care, then I'd recommend having the converters removed and weld in resonators like these (link) that look a lot like a spun style catalytic converter. This will pass a visual inspection if you've got a cop in a bad mood.

Whatever you do, make sure you keep your factory cats. Find a scrapper that will pay you fair for them based on the numbers on them. You can wire brush and google the numbers to get a rough idea of the value. Lots of folks will try to under-pay to turn around and make a bigger profit.

Of course, all of this depends on your state and local's emissions practices. If you have to pass an emissions test, make sure you get a 48 or 50 state certified converter. Though, sounds like it's not an issue in your area.

And to answer the concerns listed - you will notice no difference in power or fuel mileage, unless your converters are impeding exhaust flow in which case you will notice an increase in power and fuel mileage. Driving around with clogged catalytic converters *will* damage your engine over time.

Last question - have you changed spark plugs? At that mileage, it's due if they haven't been done and could be the cause of your issues.

Ammendum: after actually getting the links, the price is the same now between the resonators and the converters. When I did mine the resonators were half the price of the converters. Use your own judgement.

depends on where you live here in lib-fornia they check the cat's for the c.a.r.b. stamp which has to match the vehicle year/make/model and engine size, so you can't just throw anything on it.

 

[Tonyrodz]

Maybe try this first.
Cataclean 120007 Complete Engine, Fuel and Exhaust System Cleaner, 473 Milliliter (Packaging May Vary) https://a.co/d/6oPZIbq