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Catalytic converter plugged?

128K views 68 replies 38 participants last post by  kaya 
#1 ·
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 ·
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.
 
#3 ·
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.
 
#4 ·
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"! :hopeless
 
#5 ·
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.
 
#6 ·
Hmmmm, Stuck open therm. kinda sounds like your on the right track....:undecided Whats the call on dealer replacment for free? Didn't I read that somewhere???? :m2:
 
#8 ·
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).
 
#9 ·
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!!!
 
#10 · (Edited)
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)
 
#59 ·
O2 sensors vs Cat converter

Hi Jimmyjam, I thought if you removed the O2 sensors and the power returns, it was the O2 sensors? :confused: If the stuck open tstat is the causing problem for the cat clog, should you install a new tstat or can that be fixed? I have noticed a slight decrease in acceleration and a change in gas mileage in my 02 TB. I used octane booster and noticed an improvement in my gas mileage, but it's still not right. I also had an oil change using a FRAM High mileage oil filter (since it was put in I have heard bad things about that type of filter); could that be the problem? The oil filter makes the engine sound like a 18 wheeler!:confused:

I love this site; am learning a lot about my 02 trailblazer!
 
#11 ·
I have a 04' TB EXT 4.2, I started losing power when the engine got over 210 degrees. I thought it had something to do with the fan clutch so I replaced it. The fan clutch did not help. Then I got two P codes, P0172 and P0132. Both codes deal with rich condition at the upstream O2 sensor. I replaced the upstream O2 sensor, truck still had no b*lls. I looked at this post and started thinking maybe it's the cat. I called a muffler shop and asked how much a new cat would cost, they quoted $230 plus tax. The problem was they where closed for the day. :( The guy told me to drill holes in the exhaust before and after cat, he could always weld them back up. I drilled the holes and found it was the cat. I never heard of doing this before, what a great way to figure out if you have a plugged cat!:)
 
#12 ·
Sluggish issues / out run by a mazda protge 4 dr

:cry:Hey Guys I'm new the trailbalzer world.
I have a 05 ext 4x4 lt with a 4.2 vortec it have about 112000 miles.

ITS a SLUG

it has terrible acceleration I got jumped and out run by a mazda protge 4 dr today.

I was told maybe the plugs so I changed them and the air filter.

in park with the pedal to the floor it only revs 3000 going down the road it sound like the motor is killing itself just to run 60 mph

if I stand on it it revs to 5000 and kinda stays there then shifts but i'm not really accelerating much.

In reading the post it sounds like my converter is stopped up??????
 
#17 ·
:cry:Hey Guys I'm new the trailbalzer world.
I have a 05 ext 4x4 lt with a 4.2 vortec it have about 112000 miles.

ITS a SLUG

it has terrible acceleration I got jumped and out run by a mazda protge 4 dr today.

I was told maybe the plugs so I changed them and the air filter.

in park with the pedal to the floor it only revs 3000 going down the road it sound like the motor is killing itself just to run 60 mph

if I stand on it it revs to 5000 and kinda stays there then shifts but i'm not really accelerating much.

In reading the post it sounds like my converter is stopped up??????


easy,got to muffler shop,and tell him to remove the muffler the is under the engine,or clean it,because it's plugged,don't wait,this problem could hurt your engine bad!
 
#13 ·
Yes, and you should troubleshoot it to be sure before changing it.

3000 RPM limited in PARK and NEUTRAL is a programming restriction in the PCM, to reduce the amount of abuse that children could otherwise do to the tranny if they revved it up and dropped the shifter into drive. GM wanted to reduce their warranty cost.
 
#19 ·
The cat on my Trailblazer was clogged

We purchased a new 18' travel trailer and couldn't tow it above 50 mph. The engine revved and the trans went to 4,000 rpm before shifting. The dealer said the cat was clogged (87,000 miles) and wanted $950 to replace. I called GM Corp. The factory warrenty was to 80,000 miles. The girl at GM called the service department and they agreed to replace the cat for the cost of the cat alone, $250. The most important thing is that the thermostat was open for a few months before and the engine wasn't coming up to temp. The ECM would not go into closed loop until the temp is right. The engine ran rich and clogged the cat. If your stat is defective and you get the underheat code have the stat replaced immediately.
 
#20 ·
plugged cat

hey whats happinin,


you defenatly have a plugged cat. my 03 went at 70,xxx. i replaced it all with a highflow magnaflow metallic spun cat and magnaflow straight thru muffler. what a difference in power,sound,performance, and mpgs. highly recomend it. please contact me if u have any questions about this. i can tell you whatever you need to know. that is deffenatly your problem.


brian
 
#21 ·
cat

hi guys
i'm new to this site and it ROCKS! so much helpful info
i'm haveing the same lack of power issues
plan on doing a cat test and probably replacement asap
is there a way to test the o2 sensor or should i just replace it? is it hard to remove w/o a slotted socket?and what about the downstream sensor? test? replace also?
someone asked me if there are 2 cats on the 03' tbl, i don't think so, i haven't had a chance to look
 
#35 ·
hi guys
i'm new to this site and it ROCKS! so much helpful info
i'm haveing the same lack of power issues
plan on doing a cat test and probably replacement asap
is there a way to test the o2 sensor or should i just replace it? is it hard to remove w/o a slotted socket?and what about the downstream sensor? test? replace also?
someone asked me if there are 2 cats on the 03' tbl, i don't think so, i haven't had a chance to look
It is hard to check a O2 sensor. A plugged cat will cause a rich condition on the upstream O2 sensor. Try drilling a hole upstream of the cat and reset the computer. Worse case you can have it welded back up. See if it fixes your problem. Greg
 
#22 ·
How many miles on your vehicle? Lots of us recommend changing the front sensor with every plug change, if nothing else than to prevent it seizing to the manifold. If you are under 100,000 miles, then you can see the performance of the front sensor easily with a good OBDII scan tool with a live readout function.

Front sensors may fail suddenly but they are far more likely to just deteriorate in their performance because the critical sensor part is right in the exhaust stream.

Rear sensors rarely fail and will likely last the life of the vehicle. They don't contribute anything to the drivability; they only measure the performance of the cat.

Replacing the front sensor can be easy if it is not seized to the manifold. You cut off the wire and use a deep socket with a long breaker bar to remove it. You will only need the special slotted socket to replace the new one. (Don't use the slotted socket to remove the old one. It WILL slip.)

Don't bother replacing the downstream sensor. And, yes there is only one cat. (Plus a muffler, plus a resonator.)
 
#23 ·
Don't bother replacing the downstream sensor. And, yes there is only one cat. (Plus a muffler, plus a resonator.)
I will disagree with this only in the event that you are changing the CAT. Then you might as well replace the downstream sensor. Otherwise, leave it alone. Of course if you're using a universal cat, then maybe you don't want to replace it, but for all the work it takes to put in a universal cat, IMO, your better off doing the OEM pipe.
 
#24 · (Edited)
Chickenhawk and Tequila if you use antiseize on the O2 threads it won't seize. If your cat clogs up you must make sure the stat is OK before replacing the cat. I had a code which turned out to be an undertemp condition caused by an open stat. The ECM(computer runs in open loop mode not monitoring any sensors) and doesn't go to closed loop until the engine comes to temp. The rich condition clogs the cat. As far as GM's warranty to replace the cat and stat under warranty it is 80,000miles or 5 years whichever comes first.
 
#25 ·
I had a similar issue couple years ago pulling a trailer. Light came on engine power loss or something to that extent. 45-50mph max. Cat was cherry red, cut it out welded a pipe in. Check engine light stays on but I get better gas milage now. 2003 with 86k at the time.
 
#26 ·
gaadaly in NJ we have motor vehicle inspection stations. They used too check everything on the car,truck or motorcycle but now they only plug in a computor in the OBD port. If codes are found or the light is on you fail inspection. They also check your gas cap to make sure it seals properly. You have 2 months too get the vehicle fixed and return for another inspection(window sticker tells if pass or fail). If not fixed and a cop pulls you over it is a hefty fine and they pull your registration. Brand new cars are inspected after 4 years and every 2 after that. The same for trucks and motorcyles. Actually bikes are inspected for lights,brakes,loud exhaust and proper helmet(we have manditory helmet laws in Jersey)
 
#27 · (Edited)
thanx for the feedback everyone
CH.......it has 145k . i bought it used and don't know the serv history.....am i due for a cat?.....how can i test it? or are you saying that it might just be the #1 bank sensor (code P0171). my scaner doesn't have a live reader...any other way to test it? or do i just start by replacing the sensor( if i can even get it off....i"ll spray the s@#t out of it in the A.M. and hope for the best when i get home from work)if it's seized any tips to getting it off? i don't have a slotted socket, do i need to get one to install? or can i use an open end wrench?
Doc....... i agree, if i have to replace cat i will certainly replace both sensors and be sure to use antiseize grease on them
Stu.........i also had the undertemp code p0128 but the temp gauge was reading 210 which i thought was alittle high cause when i got the car temp was running at 190-200 (or was this the under temp temp condition?) w/ no ch eng lite on. could it be that it's just the temp sensor gone bad? any way to test it? if i need to replace i will do the stat and coolant too.
sorry for so many questions...... been awhile since i had to work on my car (things have gotten so much more complicated) but getting tired of getting soaked by repair shops...........
confused?
where do i start???
::ugh:
 
#28 ·
Replace the front sensor; it's time.

They come with anti-seize already applied to the threads if you buy AC Delco brand (and you should.) To get the old one off, snip the wire and use a deep socket and a long breaker bar. To put the new one on, you will need the special slotted socket but they are cheap and can be bought at any good auto parts store. (Don't use the slotted socket to remove the old sensor; it will slip.)

If your plugs have never been changed, it is past time to do that too. Use AC Delco 41-103 plugs.

You also need to look at the CAUSE of a possible plugged cat before you consider replacing it, or you will just plug the new one up too. The most likely cause is that the thermostat has failed and is allowing the engine to run too cool, thus causing it to run too rich. (The computer thinks the engine is cold and runs a very rich mixture, which causes cats to fail after a while.)

The other possible cause is your coolant temperature sensor is going bad, and the engine only THINKS it is too cold and runs too rich a mixture. The reality is that one can't really tell if it's the thermostat and it's running too cool or the sensor and it only thinks it's running too cool, but it doesn't matter; change them both. They are not expensive and are located side-by-side, so once you have the alternator off, you might as well do both.

So ... the order you want to do this is:
#1 - If your plugs have never been changed, change them for AC Delco 41-103 plugs. Easy fix and there are good threads devoted to this in here.
#2 - Replace the front oxygen sensor with a new AC Delco sensor.
#3 - Replace your thermostat and coolant temperature sensor.
#4 - Have your cat checked out at any good muffler shop. They will remove the front oxygen sensor and replace it with a backpressure gauge. They test the pressure at idle and again at 2500 RPM. Pressure should be near 0 at idle and no more than 3 or 4 PSI at 2500 RPM.

(Here is a tip to save time and money. If you are going to have your exhaust backpressure tested anyway, buy the new oxygen sensor and take it to the muffler shop. Then the muffler shop can remove the old one for you and replace it with the new one when done the test. It will save you having to buy the slotted socket.)
 
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