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Catalytic converter failure?


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#1 Burrito

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Posted 27 September 2006 - 10:36 PM

What are the symptoms of a failed catalytic converter? My truck has a rattle when I hit small bumps on the road. The rattle sounds like it is coming from under the cab of the truck. I am also getting a very bad spark knock. Could a failed catalytic converter be causing an overheated combustion chamber? I've tried just about everything to get rid of the spark knock and am trying to figure out if my cat is bad.

2001 2500HD 6.0L
2001 Chevrolet 2500HD 4X4 Crew Cab 6.0L +/-150,000 miles
2006 Chevrolet Suburban 1500 2WD 5.3L +/-90,000 miles

#2 95Sierra2500

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Posted 28 September 2006 - 05:41 AM

There is supposedly a pressure test you can do on a cat, but there's generally a few ways to find out of it's bad or not...
1. you'll set an SES code for the cat performing below a set threshold
2. crawl under and tap on it, listen for anything rattling around
3. the aforementioned pressure test (not sure how this is done)

How many miles are on it? if it has fewer than 100,000, then IF it's bad, I believe the dealer has to replace it free of charge...but i'm not sure on that.
1995 Sierra 2500 SLE 4x4 - ext. cab, long box, 350, auto, power everything...beater for the winter

1998 Grand Prix GTP - Just a V6, but it'll hang with most V8s..whoops a bunch too with exhaust, intake, and a smaller pulley

1968 Firebird - work in progress, looking for 11's all motor

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#3 Burrito

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Posted 28 September 2006 - 10:07 AM

The truck has 106,000 miles.
2001 Chevrolet 2500HD 4X4 Crew Cab 6.0L +/-150,000 miles
2006 Chevrolet Suburban 1500 2WD 5.3L +/-90,000 miles

#4 TEE

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Posted 28 September 2006 - 12:04 PM

How much is coming out the exhaust ?

#5 tasturbo86

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Posted 28 September 2006 - 01:43 PM

Here is a link that describes the exhaust test procedure and coincidentally sells the tools to do it.

http://www.troubleco...t/articles/jds/

As far as ODBII codes, my '02 c2500 with 8.1 only has O2 sensors ahead of the cats.
This means it can not tell if the cat is doing its job or not and would not be able to throw a code. Don't know if your 2001 6.0 is the same.

In addition to the exhaust pressure test, you might buy or borrow a scanner to see what is going on in the engine. You will be able to see normal timing as well as the knock retard if present. I bought an AutoXray 4000 for a little over $200. There are many others that would be great for this purpose.

terry

#6 95Sierra2500

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Posted 29 September 2006 - 05:26 AM

Here is a link that describes the exhaust test procedure and coincidentally sells the tools to do it.

http://www.troubleco...t/articles/jds/

As far as ODBII codes, my '02 c2500 with 8.1 only has O2 sensors ahead of the cats.
This means it can not tell if the cat is doing its job or not and would not be able to throw a code.  Don't know if your 2001 6.0 is the same.

In addition to the exhaust pressure test, you might buy or borrow a scanner to see what is going on in the engine.  You will be able to see normal timing as well as the knock retard if present.  I bought an AutoXray 4000 for a little over $200.  There are many others that would be great for this purpose.

terry

<{POST_SNAPBACK}>


The reason you don't have O2 sensors behind your cat is IIRC because you've got the big block, and as such it's considered a light medium-duty truck, which do not have the same regulations on them as other vehicles. My dad's old '94 falls under those regulations as he also has a big block in his truck (454). In fact, his truck has the cat BEHIND the muffler, and if he so chose could run w/o a cat and would be perfecctly legal.
1995 Sierra 2500 SLE 4x4 - ext. cab, long box, 350, auto, power everything...beater for the winter

1998 Grand Prix GTP - Just a V6, but it'll hang with most V8s..whoops a bunch too with exhaust, intake, and a smaller pulley

1968 Firebird - work in progress, looking for 11's all motor

1999 GMC Jimmy - The wifey's ride

#7 dewfpo

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Posted 29 September 2006 - 07:23 PM

You can easily tell if a cat is working by using an IR temp gun. The outlet of the cat should be at least 100F hotter.

A rattle in the cat does not mean it is bad. Rattles on these trucks typically come from the numerous heat shields above the exhaust system.

I would recommend pulling your plugs and taking a look at them. A misfiring cylinder can let raw fuel into the cat and can overheat/melt it if it is bad enough. If only one cylinder is misfiring or knocking check for too much fuel (carbon) on the spark plug (possibly a bad injector) or too little fuel (white) on the spark plug (possibly a vacuum leak). If it's multiple cyl's, then you might have a bad knock sensor or need a good MAF cleaning, etc...

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