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Go Back   Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum > 2002 - 2009 TrailBlazer/Envoy Tech > 02-09 Vortec 4.2L I-6 Engine and Drivetrain > Exhaust Mods

Exhaust Mods Performance Exhaust Modifications

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  #1  
Old 11-03-2008, 08:22 PM
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Vortec4200 Vortec4200 is offline
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Question Catalytic converter plugged?

Although my '03 TB 4.2L (3.73 rear) has been running a lot better after a host of modest improvements, it still lacks the "oomph" of my '02 Bravada (also a 3.73 rear) clone car. I'm going on 121k miles now and I had a couple of folks on this forum who suggested the catalytic converter maybe plugged, but I mentally ruled it out because it's a 2003 model year and that seemed like a premature failure. Now I'm probably seeking a second opinion.

I had ran with a stuck open thermostat, for probably god knows how long, operating around 160 degrees according to the gauge. The problem is, I drove it around that way assuming it appeared normal because there never was a SES light. So running "too rich" for a long time could have screwed up the cat, right?

There still isn't an SES light. No cat code or 02 sensor code. Nothing. As a sidebar, here are some driveability symptoms. It still feels sluggish. For example, when you take off doing a hard launch from a standstill with the shifter in D, the engine will max rev 4000 rpm (no higher than that) in 1st gear, bogs (feels like it runs out of breath as a slight pause for a second), and then upshift into 2nd gear. If I put the shifter in L and manually shift the tranny to engage 2nd, the engine will rev out to 5000 rpm while in L (don't know if I should let it rev higher just for the hell of it but I don't want to break anything neither).

So without the SES light coming on, is it possible for the cat to be plugged?
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  #2  
Old 11-03-2008, 09:03 PM
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Quote:
Originally Posted by Vortec4200 View Post
I mentally ruled it out because it's a 2003 model year and that seemed like a premature failure. Now I'm probably seeking a second opinion.
I don't know what you are looking for here. Are you looking for an answer you like better? We gave you our opinion already and you admit you "ruled it out". On these vehicles, "premature failure" is sometimes fairly normal.

Use the search function and see how many people over the last 2 or 3 years have replaced converters, especially on 02 and 03 models.

You also admit it ran rich for an extended period of time. That is rather hard on converters. Many people have driven a long time with a bad cat and with poor performance and never get a SES light.

Based on what you said about your tranny shifting, maybe you have a transmission or PCM problem. Might be time to let a professional do some testing.
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Old 11-03-2008, 09:41 PM
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I have decided to take the advice and declare a "bad cat." Now the fun part. Which catalytic converter brand should I purchase as a replacement that is as equal or maybe better than the OEM? Actually, who makes the OEM cat? Hopefully not some China or Taiwan Autozone special lol.
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Old 11-04-2008, 12:09 AM
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Personally I would take the old cat off FIRST, and see if that helps your problems. You could live with the noise for a short time, or buy a pipe to temporarily replace the cat.

As far as what brand of cat, sorry but I have no clue as to who makes the OEM. Fortunately I haven't had to replace mine yet. Note I said "yet"!
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Old 08-17-2010, 01:00 AM
stradivarious stradivarious is offline
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Trailblazer cat converter

My experience with the cat converter on an 03 TB EXT is as follows:

I was driving on the hwy at approx. 120 km/hr when I felt a jolt and the engine seemed to have lost power; I would step on it, the engine would rev high but the truck would not go above 80 km/hr.
I thought that I had lost a gear, so I took the truck into a transmission shop for a test drive and the tech confirmed that the tranny was ok; he suggested that I had an issue with the engine.
I went home and changed the spark plugs, checked the around the engine for anything unusual and could not find a thing.
I then concluded (after reading some info on the Internet) that the cat converter could be faulty; took the cat converter out and had it replaced (by a mechanic, as I don't have a welding machine and I found it impossible to remove the darn thing from the underside of the car); truck runs normal now.
I have never had any warning lights on during this process.
Hope this helps.
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Old 08-17-2010, 12:15 PM
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Hmmmm, Stuck open therm. kinda sounds like your on the right track.... Whats the call on dealer replacment for free? Didn't I read that somewhere????
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  #7  
Old 12-12-2010, 10:48 PM
illinijeff217 illinijeff217 is offline
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Any update? Would your truck hang up at 4000 rpm for a whil then finally shift? What cat did you go with?
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  #8  
Old 12-16-2010, 12:32 AM
stradivarious stradivarious is offline
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Sorry, I do not remember which cat I bought; I bought it from Rockauto.com and it was one of the cheaper ones (less than $300 if I recall).

As far as shifting, the tranny seems to act ok, after 200,000 km it had to put up with.

To answer to the previous comment (by guano2), my experience with the dealers was not so good so I gave up a long time ago and started fixing my car on my own. As mentioned above, the truck has 200k on it; it is 7 years old, so I believe all the warranties are gone; I never purchased an extended warranty.

Knock on wood, the truck is running ok and still starting in -35 degrees C after being all night out (unplugged).
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  #9  
Old 08-03-2011, 11:57 AM
GHGore GHGore is offline
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I'll add my experience here.

I was having the same symptoms as the OP with my 2002 Envoy XL SLT. From reading Trailvoy, I was pretty sure it was also my catalytic converter. It was really starting to have major problems with taking off from stops and I've even gotten a better idea of what streets in my city has the biggest hills as my power would really bog down if I had to make it up an incline. For several weeks there I was driving in the slow lane.

I was able to find the catalytic converter on Amazon for $200... with free shipping. For the XLs make sure you get the CC assembly for the longer wheelbase, btw. Another $120 in labor charges with the local shop close to my neighborhood and my GMC Envoy now runs like a champ again.

Hopefully this helps somebody. I know I've gotten a LOT from this site in the short time that I've owned my Envoy, so hopefully I'm giving back a bit here.

Love the site!!!
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  #10  
Old 08-03-2011, 01:41 PM
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a plugged cat is easily diagnosed. unscrew the upstream o2 sensor from the exhaust manifold and go for a short drive. if the power returns, then get a new catalytic converter. and fix whatever caused it to clog in the first place (stuck open tstat probably)
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