Catalytic converter question:

[speeder]

When CCs fail, do they get plugged? Or do they just lose efficiency some other way? Do they ever last forever if no contamination enters them, IOW, vehicle is running perfectly?

I need to replace cats on my PU truck and hoping for some jump in performance/efficiency of course but I'll be happy if the CEL just goes off.

[Arizona_928]

In my experience they get clogged, or cracked. With Higher mileage they might loose effectiveness of the catalyst, but I don't think that's the leading cause....

[john70t]

CEL (check engine light) is pre-1995. OBD1.
MIL (malfunction indicator lamp) is post-1995 everything. OBDII. 16 pin connector for a scanner under the dash. Standardized everything. Some codes are proprietary and vehicle specific.

Cats will clog with a dirty engine(bad plugs/mix or oil bypass).
Sometime this can be fixed with a tuneup followed by an italian tuneup. Caveat Emptor as always.

Silicone gasket sealant will wreck cats.

Drive it an put an infrared thermometer on the tailpipe.
The pipe should be hotter after the cat. Stuff is burning up. All is well.

[aigel]

Catalytic converters by definition will not wear out. The catalyst is only "present' in the chemical reaction, lending a hand, but in no way is it consumed or changed. If you need new cats, my bet is that something is problematic up stream leading to incomplete combustion. Definitely make sure that is fixed so you don't buy new cats every few years. I have never had to replace cats and I have had several vehicles at 200k+ miles.

G

[Tobra]

As George says, the catalyst is not changed by the reaction. I think they can fail a few different ways, the substrate on which the catalyst resides can break down, or the catalyst can get poisoned, and the catalyst does not work as well or at all.

[porsche4life]

I had to replace the cats on the Chevy I had. Found them on Amazon for $250...

It had been running lean when I got it, which will burn up the cats from what I read.

[john70t]

Originally Posted by porsche4life

It had been running lean when I got it, which will burn up the cats from what I read.

Yup.
The front of two-stag cats burn up extra HC molecules. That's what they do. Hence the heat shields and no parking on tall dry grass on a hot day. Prairie fires are no good. Air injection was used with early models to help the process. OBD2 uses a lean/rich cycling method to clean the cat.
The back part converts NOX into nitrogen and oxygen. NOX is formed with lean and/or high temp burn conditions.

But if clogged, the cats prevent exhaust flow.
The heat stays in the head and then burns up valves.

[speeder]

Originally Posted by aigel

Catalytic converters by definition will not wear out. The catalyst is only "present' in the chemical reaction, lending a hand, but in no way is it consumed or changed. If you need new cats, my bet is that something is problematic up stream leading to incomplete combustion. Definitely make sure that is fixed so you don't buy new cats every few years. I have never had to replace cats and I have had several vehicles at 200k+ miles.

G

That is sort of what I thought but since the truck is running well and not throwing any other DTC codes, (and maintained up to date), I don't really know where to look. If it had so much as a random misfire, there would be a code.

During a recent repair, with exhaust manifold unfastened but still in position, some coolant spilled into it. I suspect that was what damaged the cat.

[John Rogers]

You did not mention what year and model you have and since you are in CA and the L.A. area the replacement cat, if you decide to get one has to be CARB approved. I went through this in the last year with both our cars. First my wife's 2003 Caddy Deville, V8 needed one and in that case there are aftermarket CARB approved that can be used and I had the shop install one. For my 2007 Chevy HHR with the 2.4L four, there were no aftermarket ones and only the dealer can sell them. Seems CA, in their wisdom has really raised the costs to have the cat certified, something like $75,000 for each model, sooooo the aftermarket folks said screw it! By default the dealer has to be able to sell a cat and for my car it was $850 parts and $250 labor since the smog warranty had expired as I have 135,000 miles on the car.

If the code being thrown is something like P0420 then it could be a bad down stream O2 sensor as they will fail and generate the cat efficiency low error code. The upstrean O2 voltage should jump as the engine runs and revs where the downstream O2 may bounce a little but should stay nearly constant! My friends at Black Forest Porsche repair in San Diego say to put in new O2 sensors at 65K miles since the gas we have in CA is so loaded with anti smog goop it is as bad as leaded gas anymore. I tried that, cleared the codes but after a while it would come back!

If you try to buy a cat from a place such as ********.com, they will not ship one to your CA address, no matter how much you plead with them as I tried, BUT they will ship one to Nevada or Arizona! The cats they sell are the exact same as the dealer ones, soooooooo....... I have mine replaced now, no more codes and millage has gone up so I think it was restricting exhaust flow somewhat? As far as I know, you will probably have to manually clear the code(s) depending on what is thrown after the work.

[speeder]

I am in the Midwest and this truck has never been in CA., so that is not an issue. I'm aware of the whole *will not ship to CA., (or NY)* deal. I just ordered a whole new assembly with pipes, both cats and seals for $280 w/ free shipping. Every shop in town wanted $1k installed for the same thing, (NAPA wanted $500+ for the part), and this is not CA. There is no welding or cutting involved, it's a bolt-in operation.

Since both cats have 165k on them and may have been contaminated/damaged, it's getting new ones. This is what I bought:

http://www.***********************/sku/Chevrolet/K1500/Evan_Fischer/Catalytic_Converter/1998/REPC960301.html?apwcid=productads&gclid=COjiw-PHiMgCFQUIaQodwvIPUQ

[cgarr]

Some cars like the VW's have an o2 sensor ahead of and behind the CC which will help with the health of the CC Now I just had a 2000 MK4 jetta VR6 come in that would not run, it started, run up to about 2000 rpm then shut down. Turned out a chunk of the CC got lodged at the muffler and there was ZERO exhaust going thru. I have never seen one so air tight it would not even start!

[GWN7]

They can collapse and will block the exhaust.

Here's what the material looks like from one that had partially collapsed.

It's sort of a stranded material.

Cut one cat (it had two) off a 86 Lincoln I scrapped last week and someone had cut it open, cleaned out the material and then re-welded it closed.

[GWN7]

Originally Posted by cgarr

Some cars like the VW's have an o2 sensor ahead of and behind the CC which will help with the health of the CC Now I just had a 2000 MK4 jetta VR6 come in that would not run, it started, run up to about 2000 rpm then shut down. Turned out a chunk of the CC got lodged at the muffler and there was ZERO exhaust going thru. I have never seen one so air tight it would not even start!

My 98 Chev Silverado had two O2 sensors. They read the exhaust before and after the cat. The computer adjusted the fuel based on what they read.

[John Rogers]

Well it looks like the cost of having cat(s) replaced is the same all over the country? I'd recommend putting in new O2 sensors since the old cats probably caused them to get corrupted? If the truck has upstream and down stream you could try just downstream but probably better off doing all of them?

[speeder]

I think that all halfway modern vehicles have sensors before and after the cats. The ones downstream from cat have nothing to do with how the engine runs, they simply monitor the cat. And throw a code if it's not doing its job, like mine right now.

If my primary O2 sensors were bad, that would be a separate DTC. There is no such code present.

[GWN7]

The computer reads the front and rear O2 sensors. It then adjusts your fuel based on the difference it is supposed to read from the two.

[john70t]

Originally Posted by cgarr

Some cars like the VW's have an o2 sensor ahead of and behind the CC which will help with the health of the CC

The OBD2 system(1995 on) requires O2 sensors before and after the cat.