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2002 gmc envoy_slt_xl
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02 envoy 260,000 kms, i have noticed a gradual loss of power over last 40,000 km , just had tranny rebuilt so thats not it i believe, i've had the fan clutch issue before so i know thats not it, plugs have been replaced compression all around 170 on the highway it wouldn't go above 4000 rpms and is gutless going up a hill, i'm figuring the cat , going to check pressure at the o2 sensor but i'm not sure what it should be? i read it somewhere before but cant locate it now.....any thoughts?
thanks :)

oh btw i still get about about 600 k on a full tank on the highway i have the xl so ita an 85 litre tank
 

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2005 chevy trailblazer_ls_ext
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02 envoy 260,000 kms, i have noticed a gradual loss of power over last 40,000 km , just had tranny rebuilt so thats not it i believe, i've had the fan clutch issue before so i know thats not it, plugs have been replaced compression all around 170 on the highway it wouldn't go above 4000 rpms and is gutless going up a hill, i'm figuring the cat , going to check pressure at the o2 sensor but i'm not sure what it should be? i read it somewhere before but cant locate it now.....any thoughts?
thanks :)

oh btw i still get about about 600 k on a full tank on the highway i have the xl so ita an 85 litre tank
Okay, let's start by converting to miles and gallons, that most of us non metric people can understand.

You say you get 600 kilometers to a full tank. According to my google calculations that is about 373 miles. 85 liter tank? That is roughly 22 gallons? All EXT and XL have the 25 gallon tank which would be around 95 liters.

But your statement about 600K on a full tank doesn't really tell us much. When you fill up, do you have 1 gallon left or 4? If it's 1 gallon, you are getting roughly 15.5 MPG, if you have 4 gallons left it's 17.8 MPG

373/ 24 = 15.5
373/ 21 = 17.8

Also you didn't mention what type of driving you do on the 600 kilometers. Is that all city, mostly freeway or what? This is a case where we need more information.

I would say it's possible your cat is on it's way out. Is your CEL light on?
 

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2003 gmc envoy_slt
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7,190 Posts
02 envoy 260,000 kms, i have noticed a gradual loss of power over last 40,000 km , just had tranny rebuilt so thats not it i believe, i've had the fan clutch issue before so i know thats not it, plugs have been replaced compression all around 170 on the highway it wouldn't go above 4000 rpms and is gutless going up a hill, i'm figuring the cat , going to check pressure at the o2 sensor but i'm not sure what it should be? i read it somewhere before but cant locate it now.....any thoughts?
thanks :)

oh btw i still get about about 600 k on a full tank on the highway i have the xl so ita an 85 litre tank
I'm confused (again). You say you have a question about a 2002 Envoy, which would have the 85 ltr gas tank. Then you say it is an XL, which would be a 95 ltr tank. But, as I understand it, the XL didn't come out until 2003. It doesn't mean much for your problem, but as I said, I'm:confused:.
 

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2003 chevy trailblazer_lt
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49 Posts
I'm confused (again). You say you have a question about a 2002 Envoy, which would have the 85 ltr gas tank. Then you say it is an XL, which would be a 95 ltr tank. But, as I understand it, the XL didn't come out until 2003. It doesn't mean much for your problem, but as I said, I'm:confused:.
Any difference in the Canadian models and the US models as far as when the XL was released?
 

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2003 gmc envoy_slt
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I really don't know. I'm just going by the owners manual PDF listed in the Resources section. There is no mention of XL fluid capacity or fuse box differences. Also in your question you call it a 2002, in your info you have a 2003. Do you have two different Envoys?
 

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2002 gmc envoy_slt_xl
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Discussion Starter · #7 · (Edited)
okay, when i joined i thought it was a 03 but it is an 02 my mistake, i have corrected it . forget the liters and km's as thats not the issue it was a comment that i get about 600kms to 85litres of combined driving as i always have (generally i fill it up before it is completely empty) i do have the 95 litre gas tank as i have replaced the fuel pump and delt with the filler neck issue. Its a canadian model and the manual is a 2002 so they must have released them earlier up here..that truly amazes me tho that we had something released to us up here before the U.S., i always thought we got the cast offs. The throttle body has been removed and cleaned and the battery disconnected to reset . it has 260000 kms on it and i'm thinking looking at other posts that the cat may be clogged causing the lack of power on acceleration or under load. was curious if thats what others have found when the cat was going
thanks ,i do appreciate the banter :)
 

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2003 chevy trailblazer_ls
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Appears that 600Km= 372 miles.
85L=22.4 gallons.

373/22.4 = 16.6 mpg

that 16.6 appears a little low if youre doing all highway miles. (flat and reasonable speed)....

But the bogging down on hills is what most describe on the bad cat... or when trying to pass a car it bogs down.

Have you changed your 02 sensor?
It may be lazy and not setting the CEL lamp...
 

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2008 gmc envoy_slt
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But the bogging down on hills is what most describe on the bad cat... or when trying to pass a car it bogs down.
This is what I'm experiencing now with 18,800 miles! Could it indeed be a clogged cat at this mileage? No lights or codes.....runs pretty well except for previous noted, although MPG is rather low, (about 12-13 @ 95% less than 2 miles day average...doesn't get warmed to temp except on weekends):ugh:
 

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2005 chevy trailblazer_ls_ext
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But the bogging down on hills is what most describe on the bad cat... or when trying to pass a car it bogs down.
This is what I'm experiencing now with 18,800 miles! Could it indeed be a clogged cat at this mileage? No lights or codes.....runs pretty well except for previous noted, although MPG is rather low, (about 12-13 @ 95% less than 2 miles day average...doesn't get warmed to temp except on weekends):ugh:
I would say that is normal MPG for that type of driving. Your engine is basically always warming up and as you noted not quite up to operating temp.

I'd check your air filter first. While it's possible for a cat to be plugged at your low mileage, I'd say it's not likely.

Since you are still under warranty I'd take it a dealership and have them check it out. I know it's not pleasant and sad thing is they are PROBABLY going to say "It's normal".

Have you changed your 02 sensor?
It may be lazy and not setting the CEL lamp...
Though I'd agree the 02 sensor may be lazy - I was under the impression that at or near WOT (Wide Open Throttle) the PCM does not use information from the 02 sensor. At least that's the way it was on some of my other vehicles, most of which were the old OBD1 system.
Maybe someone who does tuning or has the tuning software can correct me if I'm wrong.
 

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2005 chevy trailblazer_lt
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02 envoy 260,000 kms, i have noticed a gradual loss of power over last 40,000 km , ......... on the highway it wouldn't go above 4000 rpms and is gutless going up a hill, i'm figuring the cat , going to check pressure at the o2 sensor but i'm not sure what it should be? i read it somewhere before but cant locate it now.....any thoughts?
thanks :)
Wow - tough crowd.
I hope you found the other posts that give symptoms of a bad cat and if there's a way to test it.
 

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2002 gmc envoy_slt_xl
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Discussion Starter · #12 ·
Actually ,it seems to have way more power and less slugishness on startup before is gets to operating temperature, so i wonder if this is a sign of a lazy O2 sensor as maybe the engine doesn't use its input untill it gets up to normal operating temperature....or a combination of o2 sensor and clogged cat.
saw a utube post on checking cat pressure before and aft the cat
 

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Basic Vendor- Skid Plates
2007 chevy trailblazer_ls
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Actually ,it seems to have way more power and less slugishness on startup before is gets to operating temperature, so i wonder if this is a sign of a lazy O2 sensor as maybe the engine doesn't use its input untill it gets up to normal operating temperature....or a combination of o2 sensor and clogged cat.
saw a utube post on checking cat pressure before and aft the cat
I have no experience with clogged cats, but I'll tell you that modern vehicles (2000+) are only open loop for around 12 seconds after startup...

Mike
 

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ok....when my cat went bad it would not go over 3500rpm and it was 75% clogged.......my exhaust manifold cracked..i would assume from the heat and back pressure....so keep in second or third gear and run up to 5500rpm...this would give you max volume output so if cat is plugged it wont go that high
 

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2002 gmc envoy_sle
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Just finished an 800 mile trip (back to NY). Thru the PA mountains I started bogging down on the hills WTF now!! Scary stuff when the signs read like, "Fog and Construction for next bazillion miles". So we limped in and I read the codes - bad O2 sensor. I didn't have the time to fool with it so I took it in to my friendly local mechanic. A hunnert fifty bucks later I'm back on the road with a shiny new upstream sensor.

I cleaned the throttle body last month and was looking for the gas mileage to improve - and it did, at least until the O2 sensor started mucking up. Went from an average of 19.5mpg to 21.5mpg - me likee:yes:
 

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2002 gmc envoy_slt_xl
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Discussion Starter · #16 ·
wooooo hoooooo

well a big part of the prob solved....pre cat pressure is suppose to be no more than 1.25 psi at 2000 to 2500 rpm. we tested it and it was up to about 4 psi with jumps up to 8 psi at higher revs, so changed cat and now my power is back and fuel ecomony hugely improved, but have only driven it about 5 miles in the city. i will post more. now we are wondering if it was because the engine was running too lean? maybe o2 sensor although it appears to be reading correctly on driving or are we analyzing this too much and it was just an old cat with 162, 000 miles on it. I would say it started going at about 140,000 and slowly got worse over time.
 

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2003 gmc envoy_slt
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IIRC it is from running too rich. The cat has to burn off the excess fuel which causes it to melt and clog. Now, slightly:eek:fftopic:: Did you get a discount on the new cat? I've heard of low-life scum steeling cats off of cars because of the platinum in them. Just wondering if you, or anyone else, were given the $100 that scrap dealers are paying?
 

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2004 gmc envoy_sle
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haveing prob

i have 2004 envoy and i filled up on gas went about 250 miles got between 1/4 and 1/2 tank and it started spitting and sputtering and died i changed fuel filter then put fuel treatment in and now it wont hardly run at all my exaust warm from engine to catalack but it alot hotter what dose anybody think my prob is shold i replace the cat thks dj
 

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2002 chevy trailblazer_lt
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Another thing to look at

docdrs -

I just had my cat replaced also. Although I am not seeing much MPG improvement yet, I am happy with the performance of the car.

Since you have an '02 you may want to consider changing the fuel filter if you have not already done so.
 
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