Catalytic Converter - Going Bad?

[Plimbob]

I think the CC is going bad on my 07 Tahoe (257,000 miles). I was pulling the boat out in the hills in central SD going to Lake Oahe fishing and noticed it was really struggling going up the hills. Noticed a faint rotten egg smell every once in awhile. However, no check engine light ever came on.

Wondered how you actually can tell without removal?

 

[PG01]

I think the CC is going bad on my 07 Tahoe (257,000 miles). I was pulling the boat out in the hills in central SD going to Lake Oahe fishing and noticed it was really struggling going up the hills. Noticed a faint rotten egg smell every once in awhile. However, no check engine light ever came on.

Wondered how you actually can tell without removal?

Yes the cat csn be going bad but it will usually set a cel. 2 things.... you may have got the bottom of the tank at your last fill up and the sulpher in the stations tanks isnt burning off, i would go to a premium top tier gas station, mobil, sunoco, etc and fill up with a super or super plus octanewise, as in 91-93 octane and give it a few days to work through. Then i would get a good code reader/scanner, one that you can monitor certain engine parameters and take a look at your o2 sensors. This is an easy way to see if the cats are performing correctly. Look at bank 1 and bank 2 upsteam and downstream o2 sensors. There are four, 1 before each cat and 1 after upstream os before downstream is after they should all have a nice and even line and not look like this.

You can also take a temp reading at the front and rear of the cat, the two temps should be relatively similar, no large temp diffs

 

[gpracer1]

Yes the cat csn be going bad but it will usually set a cel. 2 things.... you may have got the bottom of the tank at your last fill up and the sulpher in the stations tanks isnt burning off, i would go to a premium top tier gas station, mobil, sunoco, etc and fill up with a super or super plus octanewise, as in 91-93 octane and give it a few days to work through. Then i would get a good code reader/scanner, one that you can monitor certain engine parameters and take a look at your o2 sensors. This is an easy way to see if the cats are performing correctly. Look at bank 1 and bank 2 upsteam and downstream o2 sensors. There are four, 1 before each cat and 1 after upstream os before downstream is after they should all have a nice and even line and not look like this. View attachment 203980

You can also take a temp reading at the front and rear of the cat, the two temps should be relatively similar, no large temp diffs

Actually the upstream O2s are used for fuel management (bank 1 sensor 1 and bank 2 sensor 1) and the lines should be continuously oscillating like the green one in your picture....that’s normal unless coasting down a hill or full throttle.

 

[PG01]

Actually the upstream O2s are used for fuel management (bank 1 sensor 1 and bank 2 sensor 1) and the lines should be continuously oscillating like the green one in your picture....that’s normal unless coasting down a hill or full throttle.

Yes this is at 55mph and no it should not be ‘oscillating’ this much, the downstream or sensor 2 needs to be more steady and not spike or drop off as quickly as this one is. And yes that determines how efficiently the cat is burning off and with the front 02’s, upstream, tells the computer to add or remove fuel...... in simple terms....

 

[gpracer1]

Yeah the green one in the pic looks like a normal UPSTREAM sensor. I noticed it’s labeled as DOWNSTREAM on the graph which means it’s reading the same as the upstream or non functional cat.

 

[Plimbob]

Thanks Guys for your responses. I don't currently have a scanner capable of doing what you describe. I'll probably have to take it in to have it checked.

Again, thanks much for you taking the time to answer.

 

[RET423]

A plugged Cat will cause a power loss, it will not create the rotten egg smell.

It sounds like you have one or both of your upstream 02 sensors reporting a false lean condition, I would say a possible injector but you would feel a miss if an injector was leaking into a cylinder when it should be closed.

02 sensors get coated with soot and can't accurately read the oxygen content, they can be cleaned but they are cheap enough to just replace. If it is a rich condition (the rotten egg smell) then I would change out the upstream 02 sensors before buying catalytic converters.

A rich mixture stinks and robs power, the computer won't throw a code as long as the signal from the 02 sensors is within its appropriate range. The computer has no way of determining if the signal from an 02 sensor is correct, only that it is sending a signal that it in the appropriate voltage range; if that is a false lean then the computer will increase the fuel supply in an attempt to get the reading it wants from the 02 sensor but it won't throw a code.