08 Alpha Catalytic converter individual replacement, why not?

[lfootmatt]

Besides tight clearances, is there any technical reason not to individually replace each cat?

Mine are shot, and constantly throwing code P0420/P0138 and won’t pass emissions. Probably doing the extender trick for the short term.

At close to $1000 to replace both driver’s and passenger side cat assemblies why not weld in similar sized aftermarket replacement cats?

That said, my buddy who builds tube framed race trucks from the ground up will weld them in. I see no reason not to gif them up, measure and cut while keeping the same configuration. The free expert welding certainly helps!!!

Anything I’m missing?

Thanks,

Matt

PS it seems the search function on this forum does not work well anymore. And I find more on this for him by going straight to google and search in the terms.

 

[Nikal]

Not on a H3, but I have a Silverado with the same 5.3. I had a cat go bad and the dual cats & Y pipe was $1200 for just the part & dealer only. I called a shop here in San Diego named Ed Hansons. They are a full exhaust shop, and do lots of custom & hot rod exhausts. They said they could cut my factory cats out of the Y pipe and weld in new ones that are fully CARB & smog legal. The brand of cats installed were Walker and two cats installed was around $500, and has a better warranty then OEM dealer cat & Y pipe.

 

[lfootmatt]

That's what I'm thinking. The only limitation I see on the H3 Cats are their tight clearances and small size. My guy is an expert welder and confident we can jig it up and get the angles to match.

He's also got an extra double knuckle/double cardan CVish joint he's going to build into a front driveshaft.

Killing 5 birds with 1 stone, 4 cats and 1 driveshaft!

Later,

Matt

 

[lfootmatt]

Used the Dorman 18mm X 1.5 gasketed spark plug nonfoulers, drilled completely out using a 1/2” drill bit. Codes cleared and haven’t returned.

Short term remedy while we replace the cats.

 

[650Hawk]

Had the driver side cat start throwing codes on mine; used the spark plug non-fouler. That was at least 4-5 years ago; haven't had the code return and passes smog easily.

Not sure how anal they are in AZ, but in CA most smog technicians will look closely at the cats; if they look like they have been replaced/modified--Fail. And very few (if any) aftermarket cats are legal in CA for the H3.

 

[lfootmatt]

AZ seems pretty lax, if it’s there you’re good. Still, I’d like to get it right without spending $1000 on parts.

Later,

Matt

 

[Nikal]

Had the driver side cat start throwing codes on mine; used the spark plug non-fouler. That was at least 4-5 years ago; haven't had the code return and passes smog easily.

Not sure how anal they are in AZ, but in CA most smog technicians will look closely at the cats; if they look like they have been replaced/modified--Fail. And very few (if any) aftermarket cats are legal in CA for the H3.

That’s not true. There are carb compliant replacement cats. Just go to a reputable muffler shop as they sell & install them. I’ve done replacement cats on two Chevys, one with the 4.8 V8 and the other 5.3. Both times the muffler shop cuts out the failed cats and welds in the carb compliant replacement cats. The brand installed were Walker and I think in the Tahoe was Magnaflow? Again both are California Carb legal and both have been smogged since.

Now I don’t know if Joe Public can buy these cats themselves? It might be only available to professional exhaust shops?

 

[lfootmatt]

I’ve been looking and it seems the CA compliant CATs are available to the public, just more costly. AZ is less restrictive.

I believe the intimidation factor with the H3 is simply the right clearances.

Later,

Matt

 

[Jeepwalker]

Before you replace the cats, do a real thorough root-cause investigation of what might have caused them to fail in the first place. Usually it's a slight cooling system leak (headgasket, etc). Oil leaks can coat them too. But minor cooling leaks will do it. Of course they can fail by age too, or break internally. But you'd hate to install new cats only to have them fail soon.

 

[Jeepwalker]

BTW, what's the deal on these. I honestly don't know. But I've seen them for a while now:

Hummer H3 3.7L Manifold Catalytic Converter 2007-2010 12H41-848 | eBay

Manifold Catalytic Converter Direct Fit. The pipe constructed from 14 gauge tubing, with original OE style heavy duty Stainless flanges, INNER BRAID FLEX PIPE and High loaded OBDII BY DESIGN Catalytic Converter.

www.ebay.com

 

[EndeavoredH3]

Before you replace the cats, do a real thorough root-cause investigation of what might have caused them to fail in the first place. Usually it's a slight cooling system leak (headgasket, etc). Oil leaks can coat them too. But minor cooling leaks will do it. Of course they can fail by age too, or break internally. But you'd hate to install new cats only to have them fail soon.

This.

 

[lfootmatt]

I get the cause ID, but this thing doesn’t use any oil or coolant. It just looks like old worn out cats.

 

[Jeepwalker]

I get the cause ID, but this thing doesn’t use any oil or coolant. It just looks like old worn out cats.

That's certainly possible. ..I was just throwing it out there.

Did you recently replace sensors? Sometimes new sensors are more sensitive (less worn) and the computer probably recognizes new O2's and the computer is recalibrated.

You have to do regular emission tests out there I suppose, huh?

 

[lfootmatt]

Yeah I replaced the drivers side rear o2 sensor, no change. And yeah, emissions annually in AZ.

Oldest boy has it in Kansas for 5 years, no emissions, so the occasional code wasn’t a worry. He got a new truck, winning a natty has that effect on the local car dealerships! Thanks you SCOTUS for NIL!!! Gave his little brother the H3 Alpha.

Rock Chalk!

Matt

 

[650Hawk]

That’s not true. There are carb compliant replacement cats. Just go to a reputable muffler shop as they sell & install them. I’ve done replacement cats on two Chevys, one with the 4.8 V8 and the other 5.3. Both times the muffler shop cuts out the failed cats and welds in the carb compliant replacement cats. The brand installed were Walker and I think in the Tahoe was Magnaflow? Again both are California Carb legal and both have been smogged since.

Now I don’t know if Joe Public can buy these cats themselves? It might be only available to professional exhaust shops?

Sorry, but you're talking about Chevy trucks, not Hummer H3s. Most manufacturers do not make CA compliant Cats for the H3 Alpha. Yes, I understand, there are plenty of 5.3s that ARE available. The problem is that CARB requires Cat's to be tested/certified for each and every specific vehicle/engine/drivetrain that it's going onto, no exceptions. And since that is that is an expensive process, the manufacturers are only willing to do it if there is a likely return on their investment. There are relatively few H3 Alpha's out there, so that ROI is unlikely. Magnaflow lists them for the H3 Alpha, but they are $1253 for the right or left rear, $2085 for the right or left front, AND cutting and welding is required; they are not bolt on replacements. Walker doesn't list one for the H3 period. Very few companies make CA compliant Catalytic Converters for the H3 Alpha (EPA compliant is NOT CARB compliant). And most reputable Smog Check businesses are not willing to overlook that since they would lose their license.

 

[lfootmatt]

650,

Good thing I'm in AZ and not in CA!!! Can't stand CA! My perfect unicorn 2007 Ram 2500 Lariat Megacab 6.7 Diesel with 68,500 grandpa driven miles got side swiped on the highway in LA last week. So pissed!!! Seriously jacked up the rear driver's side door.

Back on topic, got it through emissions, but am still putting new cats on it just because I want to ensure they are not plugged up either.

Later,

Matt

 

[Teahead]

my alpha with 170k miles seems pretty sluggish.

about 40k miles on a Jasper reman engine the PO put in.

no codes, but I'm thinking cats are clogged.

should I replace them?

 

[rascole]

If you motor is running perfect, the cats should last 300k or more. My sons 01 5.3 we replaced at 320K, my 01 5.3 replaced at 150k because bad head gasket leaked coolant in the chamber. My moms 01 5.3 had the same code that I chased for months. Was a combination of passenger side rear O2 sensor frayed wire, vac hose leak, failing EGR valve & stuck AIR valve. Not familiar with the Alpha setup but most times it is not the cat. Use a bi directional scanner, they go into far better detail. Watch the O2 voltages on start up, if it is flat lined it is failed or bad harness. Worst case delete the rear cats, they are not monitored and are for tail pipe emissions polishing only.

 

[650Hawk]

my alpha with 170k miles seems pretty sluggish.

about 40k miles on a Jasper reman engine the PO put in.

no codes, but I'm thinking cats are clogged.

should I replace them?

If you're not getting codes, the Cats are working fine. But hey, it's your money.