Possible Cat Converter Problem.

[BourbonNcigars]

Noticed I'm getting the telltale rotten egg smell (no matter where I got fuel) when I get out of my 2010 Tahoe (113K miles). More worrisome is that I've smelled it inside while driving 70mph. I was quick to blame my daughter but I knew what the smell really was. I've never messed with exhaust systems before but I know that smelling anything related to the exhaust inside the cabin is no bueno.

Here's the small amount that I do know:

• Often smell rotten eggs when getting out of Tahoe (have tried different fuel), but not every time
• Have now smelled it inside the cabin for a few seconds (twice) while on the highway
• I can see what looks like a black burnt spot on corner of the muffler if that matters
• Haven't noticed any holes anywhere but will look again
• There's a slight but constant metallic rattle that I can't find after removing the entire interior panels (possibly coming from under the vehicle?)
• No CEL or codes

What's my next step here? Any help is appreciated.

 

[kbuskill]

Noticed I'm getting the telltale rotten egg smell (no matter where I got fuel) when I get out of my 2010 Tahoe (113K miles). More worrisome is that I've smelled it inside while driving 70mph. I was quick to blame my daughter but I knew what the smell really was. I've never messed with exhaust systems before but I know that smelling anything related to the exhaust inside the cabin is no bueno.

Here's the small amount that I do know:

• Often smell rotten eggs when getting out of Tahoe (have tried different fuel), but not every time
• Have now smelled it inside the cabin for a few seconds (twice) while on the highway
• I can see what looks like a black burnt spot on corner of the muffler if that matters
• Haven't noticed any holes anywhere but will look again
• There's a slight but constant metallic rattle that I can't find after removing the entire interior panels (possibly coming from under the vehicle?)
• No CEL or codes

What's my next step here? Any help is appreciated.

If you have an OBD2 scanner that hooks up to your phone you can download the Torque Pro app and monitor your cat temperatures via the down stream O2 sensors. That would give you some more info.

Alternatively, if you have an infrared thermometer you could slide under the truck while it's running and up to temp and check the temps pre and post cat.

Also you can get an inspection camera that plugs into your phone and then pull the up stream and down stream O2 sensors and insert the camera to get a visual of the catalyst's condition.

OR you can take it to an exhaust shop and have them check and diagnose.

I see roughly 565° after idling for 15-20 minutes when the engine is up to temperature. And upwards of 11-1200° while cruising at highway speeds depending on speed and load. These temps are gathered via Torque Pro from the down stream O2 sensors.

Rotten egg smell and a possible rattle are pretty good indications of a failing cat though.

 

[BourbonNcigars]

If you have an OBD2 scanner that hooks up to your phone you can download the Torque Pro app and monitor your cat temperatures via the down stream O2 sensors. That would give you some more info.

Alternatively, if you have an infrared thermometer you could slide under the truck while it's running and up to temp and check the temps pre and post cat.

Also you can get an inspection camera that plugs into your phone and then pull the up stream and down stream O2 sensors and insert the camera to get a visual of the catalyst's condition.

OR you can take it to an exhaust shop and have them check and diagnose.

I see roughly 565° after idling for 15-20 minutes when the engine is up to temperature. And upwards of 11-1200° while cruising at highway speeds depending on speed and load. These temps are gathered via Torque Pro from the down stream O2 sensors.

Rotten egg smell and a possible rattle are pretty good indications of a failing cat though.

Thanks. I do have a thermometer to check the temps with. What am I looking for exactly? Similar to what you're getting above I assume...

Say it is bad, though...what's the replacement options? Dealership or aftermarket the way to go? I have zero desire to have a louder exhaust. I'd actually prefer a quieter one if such a thing exists in the aftermarket exhaust world.

Also concerned with why it'd go bad at 113K miles. I've had several vehicles with way more miles that didn't have an issue with a cat. Makes me wonder what the root cause is.

 

[kbuskill]

Thanks. I do have a thermometer to check the temps with. What am I looking for exactly? Similar to what you're getting above I assume...

Say it is bad, though...what's the replacement options? Dealership or aftermarket the way to go? I have zero desire to have a louder exhaust. I'd actually prefer a quieter one if such a thing exists in the aftermarket exhaust world.

Also concerned with why it'd go bad at 113K miles. I've had several vehicles with way more miles that didn't have an issue with a cat. Makes me wonder what the root cause is.

Usually the root cause of a bad cat is too much fuel/running rich. It causes them to overheat.

I would find a reputable exhaust shop and have them replace (weld in) a new cat or two.

One thing I forgot to ask is what year is your truck?

Mine is an '08 and only has 2 cats... some of the newer trucks have a 3rd further back after the Y pipe.

@swathdiver Will have more info on those but I think it is maybe '09+

It is probably a good idea to replace both of your up stream O2 sensors when you get new cats to hopefully avoid ruining the new cats.

Alternatively you could order an OEM or aftermarket Y pipe with cats and bolt it in yourself.

 

[Doubeleive]

I replaced all 4 of my 02 sensors at 100k (that is what there rated for) , had too many problems in the past on my nbs that thing would burn a cat out at least once every 2 years, I had a cat back exhaust on it from a local shop that I think was probably part of the problem. knock on wood no problems on this truck at all so far all I have done is delete the last resonator and switched out the muffler with a dual out. Aftermarket cat's will probably run you about $165 (each) installed (if they want more than that find another shop), you might be able to find new oem ones on rockauto, dealers going to want probably around 600-800 each

 

[Doubeleive]

like ken said though it would be a good idea to look at some scans and find out what is causing the problem before throwing more money at it just to turn around and have it happen again.

 

[swathdiver]

Stephen, what grade and brand of fuel are you running? Do you frequent the same station or go wherever convenient? Low tier fuels or even Shell's 87 are known for high sulfur content and making these smells. They cats are doing their best but too much sulfur and they can fail. Switch fuels, maybe run some E85 through the system and see how it goes.

I can offer some advice if the problem is the cats.

 

[BourbonNcigars]

Stephen, what grade and brand of fuel are you running? Do you frequent the same station or go wherever convenient? Low tier fuels or even Shell's 87 are known for high sulfur content and making these smells. They cats are doing their best but too much sulfur and they can fail. Switch fuels, maybe run some E85 through the system and see how it goes.

I can offer some advice if the problem is the cats.

Thanks, James. I've been going back and forth between Shell 87 and Exxon 87, which is the same fuel I've used in every other vehicle for the last 15 years without noticing any odors. I don't think I have any E85 options near me.

Wish I had more clues to give. I do notice a decent amount of black soot around the exhaust tip...no CEL or codes...intermittent rotten egg smell when getting out of the vehicle (and occasionally while driving)...a rattle that may be coming from underneath...that's about it. To be honest I really don't have enough time with it to know what kind of mileage I'm getting, or to know if power output is diminished. I have nothing to compare it to since I've only had it about 6 weeks. I only just started tracking the MPG since this issue came up.

I'll fill up with fuel on my next tank at some other station. Anything else a layman can check?

 

[89Suburban]

Also you can get an inspection camera that plugs into your phone...

I had no idea these even existed, thanks.

 

[Doubeleive]

Thanks, James. I've been going back and forth between Shell 87 and Exxon 87, which is the same fuel I've used in every other vehicle for the last 15 years without noticing any odors. I don't think I have any E85 options near me.

Wish I had more clues to give. I do notice a decent amount of black soot around the exhaust tip...no CEL or codes...intermittent rotten egg smell when getting out of the vehicle (and occasionally while driving)...a rattle that may be coming from underneath...that's about it. To be honest I really don't have enough time with it to know what kind of mileage I'm getting, or to know if power output is diminished. I have nothing to compare it to since I've only had it about 6 weeks. I only just started tracking the MPG since this issue came up.

I'll fill up with fuel on my next tank at some other station. Anything else a layman can check?

have you looked underneath the truck at the cat's? sometimes when they are replaced the new ones will have a little odor at first then it goes away, if one of them looked pretty and shiny with fresh welds then maybe someone had it replaced before you bought it. just an idea-slim chance anyway of being the case.

 

[kbuskill]

I had no idea these even existed, thanks.

Yep... they are cheap on Fleabay... bought one for like $10. They even have LEDs on the end to light up the dark places you may want to stick them...

 

[swathdiver]

Thanks, James. I've been going back and forth between Shell 87 and Exxon 87, which is the same fuel I've used in every other vehicle for the last 15 years without noticing any odors. I don't think I have any E85 options near me.

Wish I had more clues to give. I do notice a decent amount of black soot around the exhaust tip...no CEL or codes...intermittent rotten egg smell when getting out of the vehicle (and occasionally while driving)...a rattle that may be coming from underneath...that's about it. To be honest I really don't have enough time with it to know what kind of mileage I'm getting, or to know if power output is diminished. I have nothing to compare it to since I've only had it about 6 weeks. I only just started tracking the MPG since this issue came up.

I'll fill up with fuel on my next tank at some other station. Anything else a layman can check?

Without a scan tool to see what the computer is seeing all I can offer at this point is to run some Exxon/Mobil 93, two or three tanks and see if that clears it up. If not, it's probably time for new cats.

Stay away from the cheap ones, they don't last. I put a Magnaflow Y-pipe with high performance cats on mine and sold the old ones to the scrap yard to help offset the cost. Factory Y-pipe with cats is north of $900, and @GotExhaust.com made me a good deal. It was a pain for this old man to install it, I had a mobile mechanic come out to the house and finish.

 

[BourbonNcigars]

Without a scan tool to see what the computer is seeing all I can offer at this point is to run some Exxon/Mobil 93, two or three tanks and see if that clears it up. If not, it's probably time for new cats.

Stay away from the cheap ones, they don't last. I put a Magnaflow Y-pipe with high performance cats on mine and sold the old ones to the scrap yard to help offset the cost. Factory Y-pipe with cats is north of $900, and @GotExhaust.com made me a good deal. It was a pain for this old man to install it, I had a mobile mechanic come out to the house and finish.

Roger that. I'll start with the fuel and proceed from there. Thanks.

 

[BourbonNcigars]

Just as an FYI, after listening to several Youtube snips of rattling cats, that's not the sound I'm hearing in the cabin. When I beat on the exhaust with my hand, I only get a faint noise that I really don't think could be heard in the cab...even my uninsulated ************* SSV. So maybe there's hope the cat hasn't physically ended itself already.

 

[swathdiver]

Just as an FYI, after listening to several Youtube snips of rattling cats, that's not the sound I'm hearing in the cabin. When I beat on the exhaust with my hand, I only get a faint noise that I really don't think could be heard in the cab...even my uninsulated ************* SSV. So maybe there's hope the cat hasn't physically ended itself already.

There are many ways a cat can fail. Sometimes the honeycombs will break up and begin to rattle and make noise, other times they melt and block/restrict flow and they can look perfectly fine but just stopped doing their job for some reason. The latter can often by rehabbed by getting them hot and burning off whatever got stuck to the honeycombs but sometimes not in my case. My truck ran fine save for poor gas mileage and in the end the code(s) kept setting for the cats.

 

[BourbonNcigars]

Talk about paranoia. We get stuck waiting on a train tonight. Tahoe is idling. I smell something. "You smell that?...it's my exhaust isn't it?"

She says, "That's not your exhaust. It's that". A Burger King right behind us. After she said that it was quite clear it wasn't an exhaust smell (though some would argue BK does smell like exhaust).

 

[bottomline2000]

There are many ways a cat can fail. Sometimes the honeycombs will break up and begin to rattle and make noise, other times they melt and block/restrict flow and they can look perfectly fine but just stopped doing their job for some reason. The latter can often by rehabbed by getting them hot and burning off whatever got stuck to the honeycombs but sometimes not in my case. My truck ran fine save for poor gas mileage and in the end the code(s) kept setting for the cats.

I suspect a failed fuel pressure regulator compromised my cats by dumping fuel down the exhaust. My passenger cat doesn't seem to heat up at all anymore even after long trip. I think it's blocking the exhaust flow some as my mileage has gone down some. My rear 02s are tuned out so I'm just gonna knock the cats out. ExxonMobil 93 is my go to gas now and definitely burns better..fuel trims would be out of whack if your cat is bad so it may be worth taking to a shop to see if there is a problem since cats are expensive..

 

[BG1988]

Noticed I'm getting the telltale rotten egg smell (no matter where I got fuel) when I get out of my 2010 Tahoe (113K miles). More worrisome is that I've smelled it inside while driving 70mph. I was quick to blame my daughter but I knew what the smell really was. I've never messed with exhaust systems before but I know that smelling anything related to the exhaust inside the cabin is no bueno.

Here's the small amount that I do know:

• Often smell rotten eggs when getting out of Tahoe (have tried different fuel), but not every time
• Have now smelled it inside the cabin for a few seconds (twice) while on the highway
• I can see what looks like a black burnt spot on corner of the muffler if that matters
• Haven't noticed any holes anywhere but will look again
• There's a slight but constant metallic rattle that I can't find after removing the entire interior panels (possibly coming from under the vehicle?)
• No CEL or codes

What's my next step here? Any help is appreciated.

if you had a bad cat you woulf get stoner code p0420.

 

[iamdub]

Just to echo what has been said: Switch fuels for a while and observe. If the problem persists or worsens, have it scanned by someone competent with a good scan tool. They need to see what the PCM says about the cats based on the O2 sensors and what further up the line is going on that may be a cause or result of the O2's readings. If you need new cats, avoid aftermarket replacement cats. Most, if not all have far less catalyst than the OEM ones and aren't nearly as efficient.

If it were me and I needed new cats, I'd have them deleted altogether and have the rear O2 sensors turned off in a tune. It would be WAY cheaper than replacing them with new quality cats. MS doesn't have visual inspections, right?

I had mine tuned at a local speed shop for $150. It wasn't for power, it was to turn off AFM, remove the speed limiter and a few other small things. I had them turn off rear O2s in preparation for long tube headers which would not have cats. I'd imagine an exhaust shop could splice pieces of straight pipe into the stock Y-pipe to replace the cats for a couple hundred at most. So, for half or even a third of the cost of new OEM cats, etc., you could fix it and it'll never be a problem again.

 

[BourbonNcigars]

Just to echo what has been said: Switch fuels for a while and observe. If the problem persists or worsens, have it scanned by someone competent with a good scan tool. They need to see what the PCM says about the cats based on the O2 sensors and what further up the line is going on that may be a cause or result of the O2's readings. If you need new cats, avoid aftermarket replacement cats. Most, if not all have far less catalyst than the OEM ones and aren't nearly as efficient.

If it were me and I needed new cats, I'd have them deleted altogether and have the rear O2 sensors turned off in a tune. It would be WAY cheaper than replacing them with new quality cats. MS doesn't have visual inspections, right?

I had mine tuned at a local speed shop for $150. It wasn't for power, it was to turn off AFM, remove the speed limiter and a few other small things. I had them turn off rear O2s in preparation for long tube headers which would not have cats. I'd imagine an exhaust shop could splice pieces of straight pipe into the stock Y-pipe to replace the cats for a couple hundred at most. So, for half or even a third of the cost of new OEM cats, etc., you could fix it and it'll never be a problem again.

What about the note of the exhaust and volume level? I want to keep it as quiet as possible.