Learn me aftermarket catalytic converters

I need to finally put some money into my '02 Silverado.  While it doesn't get used a bunch, it does get used and I'd like it to be legal and be a little more reliable/safer to drive.  Step one is a new cat as mine is dead and throwing codes.  Looking around, I can get a off brand one for about $200, a brand name for $700 and a GM one for $1500.  I'm cheap, so dropping $1500 (or $700) on a $2200 truck seems silly, especially considering the other things it needs. 

I'm NOT expecting factory quality for a $200 converter, but if I could get it to last a year or so, that would be fine.  I'd like to eventually replace it with a V8 and back seats, but I don't seen truck prices dropping for at least a year if not longer.  And, if I did end up keeping it and fixing it up, I'd replace the cat with a better quality, but should probably do a light rebuild on the motor first.

-Rob

Do you have any exhaust leaks upstream of the converter? Exhaust manifold gasket, donut gasket, cracks at the pipe, anything?

My experience with aftermarket converters is that you are paying for manufacturing quality and QC a lot of the time. Many of the aftermarket companies will use the same core but the $199 RockAuto special will likely have awful welds and bends and will be a PITA to get installed correctly while a $699 Magnaflow is more likely to fit straight on and have a higher standard of manufacturing.

I remember comparing aftermarket cats for a BMW one time and a cheap Walker cat had this awful Y-pipe design sloppily welded together from two pieces of pipe while a Magnaflow had a tidy pre-formed piece that looked like it was designed with much more thought to flow and fitment. But the Mangaflow was 2-3x as expensive, and OE was a whole nother league...

A lot of times the cheap ones are just plain cheap.

iATN is chock full of help requests for Subaru where they had a P0420 and replaced the converter, code came back, replaced the oxygen sensors, code came back, smoke tested for leaks, none found...  the reported Fix is always "removed aftermarket cat, installed Subaru cat".

I wouldn't use a cheapy converter unless you don't mind if it throws codes again.  $200 converter, I'd expect it to be 50/50 and the warranty is "your car has another problem, it's not the converter".  $700 might be junk but they might stand behind it if you have to buy the $1500 one.

Pete. (l33t FS) said:

Do you have any exhaust leaks upstream of the converter? Exhaust manifold gasket, donut gasket, cracks at the pipe, anything?

No clue.  Probably/maybe?  I basically work on it when something breaks.  Currently have a SES for 0420 and 0430, Cats below threshold.  I think it burns a bit of oil, has 140k plus on it and runs rich, so I'm assuming the cats are dead. Was already planning on a full tuneup, including a new maf, 02 sensors and various other bits when I did the cats.  I also need to reseal the oil pan front seal, refurbish the front suspension, get new tires, etc.  Basically a laundry list of things that need doing that I've avoided,  but trying to keep costs low.  First is to get it passing inspection, hence the cats question.

-Rob

I'd fix the runs rich problem first.  That might be the reason the converters don't pass internal tests.  If the vehicle isn't running stoich, the converters won't work.

I would not replace the MAF without a good reason to.  GM MAFs almost never go bad, and aftermarket ones are usually junk.  The only GM MAFs I have ever replaced (after the awful old 2.8s)  were aftermarket ones that were thrown at the vehicle by someone else because it had a vacuum leak or a leaking exhaust manifold gasket after a bolt or two broke, causing poor fuel trims.

I put a cheap universal one on my car (04 Matrix), and had to space the downstream 02 sensor out using the anti foul spark plug spacer trick. I suspect it does almost no catalyzing. YRMV. 

Who makes a good cat that simply does its job? 

Pete. (l33t FS) said:

A lot of times the cheap ones are just plain cheap.

 

iATN is chock full of help requests for Subaru where they had a P0420 and replaced the converter, code came back, replaced the oxygen sensors, code came back, smoke tested for leaks, none found...  the reported Fix is always "removed aftermarket cat, installed Subaru cat".

I wouldn't use a cheapy converter unless you don't mind if it throws codes again.  $200 converter, I'd expect it to be 50/50 and the warranty is "your car has another problem, it's not the converter".  $700 might be junk but they might stand behind it if you have to buy the $1500 one.

I'm OK if it fails again.  And given the other issues mentioned above, fully expect it to.  But, given the other issues with it at the moment, I'm also leery of dropping $700 on a cat that will get trashed by the burning oil or running rich before I can get them fixed.  TBH, if I can get it to pass, it'll give me a year to be legal and continue to work on it.

Or a year to drive it and wait for the market to stabilize and replace it. 

Bah, I'm being difficult and wishy washy.  Sorry.  :(

Ninja edit:  I saw your recommendation on chasing the rich running condition (I can smell it, not getting any codes), so I'll look into that first.  I assumed the codes mean the cats are dead, didn't think about it resulting from other issues first. 

-Rob

Can you not get a Magnaflow cat for a couple hundred bucks? I've not had any problems with them in the past

I'll be the dissenting opinion here.

I've run multiple Walker brand cats from Rockauto on various vehicles of mine and never had a problem. I can't think of any problem I've ever had with any Walker brand exhaust part and I've run a whole pile of them over the years. They're good basic stuff that fits and works that a working man can afford.

I had a "No 'tisn't" "Yes 'tis" argument with four techs at three different smog stations as to whether the Magnaflow universal cats on my Camaro were, in fact, catalytic converters. I finally had to get the state mechanic for the county to inspect it himself.

In reply to Cousin_Eddie (Forum Supporter) :

Walker are usually decent as long as you get an OE fit.

Catco is a dirty word.  I have had many new Catco cats on pre-OBD-II vehicles fail emissions for high NOx.

I too have used Walker and Magnaflow catalytic converters with succcess.  Walker tends to be the most economical.  I wouldn't chance catalytic converter replacement on lesser brand than these.  And honestly, I wouldn't expect either to last anywhere near as long as OEM ones.  OEM ones have to last 100k by law as emissions equipment. 

The big difference in most of what we're talking about is the level of actual catalyst material included in the converter.  There are obvious build-quality differences, but since the catalyst material itself is the expensive part, you can vaguely assume that the price reflects the effectiveness and lifespan of the effective catalization of exhaust gases.

Having said that, we're talking about a GM truck.  If we're talking about a BMW, Subaru, Jaguar, or Mercedes, you would have to pony up the big bucks to get something that works.  I have used universal-fit Walker cats without issue so far on a 98 S10, an 02 F150, and a (forget the year, but OBD2) Chrysler Pacifica.  At the shop, it was a good way to save a bit of money and pay the tech an hour or two of labor to weld it in instead of buying the expensive version and bolt it in.

Having said that, it also depends on your smog test requirements.  You're in Williamson county, right?  So no sniffer?  It's one thing to not have a CEL, it's another thing to pass a sniffer.  I lived in Travis and Williamson for a few years (Jollyville - represent) and I know there was a smog check of some sort, but I don't think there was a sniffer... at least there wasn't when I was there.

I recently bought a Prius that had the cat stolen so the PO had a shop weld in the cheapest cat they could. It does not pass readiness and throws a CEL with a P0420 code for the cat so I'm also upgrading. From my research there are 3 levels of aftermarket cats. My research is all Prius specific but most of it is pretty generic. 

1. $90 OE fit cats on eBay. Seems to be about a 50/50 chance of getting rid of the CEL. If it does work it's only for a few months. Seems like a bad choice. 
2. $300 OE fit cats like Walker. People seem to like these and have good success with them but Amazon reviews say they last around 5 years. Not the best source of info, I know. In this category there is also universal weld in units from walker or magnaflow for around $150 a piece. 
3. Universal CARB legal cats for around $200. They have an EO number and date of manufacture stamped into them and legally have to be guaranteed for a certain amount of time if I'm not mistaken. Maybe 5 years?
 

hope this helps. 

I've had good luck with the magnaflow on my 94 Miata track car.  It's survived 20 or 30k so far, probably 10k of those on track.  100% stock engine with the "bolt in" fit.

Cheap cats will usually work fine, but for a shorter amount of time. I generally expect to get 50,000 miles out of a cheap one, or 100,000 miles out of a CARB certified one. From the sounds of it, you'll be content with a cheap one for this purpose. 

AnthonyGS (Forum Supporter) said:

I too have used Walker and Magnaflow catalytic converters with succcess.  Walker tends to be the most economical.  I wouldn't chance catalytic converter replacement on lesser brand than these.  And honestly, I wouldn't expect either to last anywhere near as long as OEM ones.  OEM ones have to last 100k by law as emissions equipment. 

 

100k, 120k, or 150k depending on the emissions standard (which also depends on the model year).

For the OP's '02 Silverado, it's likely 100k.  And that has to include likely oil poisoning.  

WonkoTheSane said:

I've had good luck with the magnaflow on my 94 Miata track car.  It's survived 20 or 30k so far, probably 10k of those on track.  100% stock engine with the "bolt in" fit.

One thing here- for anyone who has to really deal with the MIL light for any state registration issues- the main issue for catalyst selection is the OBDII test for the vehicle.  And anything before '96 isn't going to have that burden.  For those, it's if you have an intrusive emissions test.  

I have had mixed luck with cheap cats, but I'd start with the rich condition. 

Thanks for the help.  I never expected the cheaper cats to last 100k miles.  Honestly, more of a short term fix to get it inspected and give me a year of watching the market and deciding if I save for something newer or spend the money on this one.  I can't recall if Williamson county has a sniffer test, I'll have to look into it.  I don't think so, but better to be sure.

More importantly, sounds like I need to do a bit more digging on other issues, like the rich condition, some of the leaks, check for other exhaust leaks, etc. 

-Rob

Rob, 

They didn't have sniffer when I lived there 4 years ago. It was just codes and readiness for ODB2 applications. I meant I got a LS3 miata to clear emissions with no problems there. 

I live in Ohio where the cars have to be checked every other year.  My Mustang (1997) will not need to be checked ever again as it will be 25 years old in 2023.   If I remove the cats will I have to change the program in the ECU?

In reply to Mustang50 :

Yes, otherwise it will throw a CEL for cat efficiency. I would imagine it is common to tune them out.

That being said, I have also regretted removing the cats from the few street vehicles on which I have done so and would recommend you either leave them in place or upgrade to performance aftermarket. Exhaust fumes aren't great to begin with, but without a cat I find they really do bother me more and make me wince in a way that makes me feel like I'm chopping years off my life, probably because of the NOx.

the cat does not have any wires or sender  so it is not throwing a code or light , 

so what does the ECU look for  and not find on the cheap cats output ?

and do the cheap cats  clog up quicker so you have the "potato in the tailpipe" problem ?