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2003 gmc envoy_sle
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Discussion Starter #1
My envoy majorly loses power on any uphill grade. Good coils, plugs, air cleaner, and motr runs smooth, Has less power the hot it gets. Code reader shows p0440, Changed gas cap...No improvement. Any suggestions before I start randomly changing solenoids and hoses in the Evap system. And Does any malfunction in the evap system cause this lack of power? :undecided
 

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2004 gmc envoy_slt
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Has fuel filter ever been changed? There is also a possibility of a clogged catalytic converter.

In order to diagnose this issue, a scan tool needs to be hooked up and certain parameters monitored when problem occurs.
 

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2003 gmc envoy_sle
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Discussion Starter #3 (Edited)
Has fuel filter ever been changed? There is also a possibility of a clogged catalytic converter.

In order to diagnose this issue, a scan tool needs to be hooked up and certain parameters monitored when problem occurs.

Thanks EnvoyBoy2004. Scan only came back with p0440, so I'm focusing on evap system first.
It over heats too, and thats when it at its weakest. Temp was around 215 and notice radiator boiling but Not blowing into reserve. So I'm gonna change radiator cap. Changed fuel filter about 2 months ago.
 

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I was not talking about reading codes, but rather live data such as fuel trims, O2 sensor performance. I would definitely look into checking out the catalytic converter.
 

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Discussion Starter #5
I was not talking about reading codes, but rather live data such as fuel trims, O2 sensor performance. I would definitely look into checking out the catalytic converter.
Thanks. I'll look into checking the cat converter also :thx
 

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2004 chevy trailblazer_ls
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Do you have any white smoke out of the exhaust?
215 degrees is not too hot on this platform. The bubbles in the radiator could be a problem.Is the overflow tank bubbling?
See if you can find one of those kits (sorry, I don't remember the name) that checks for exhaust in the radiator. If so, you may have a blown head gasket.
 

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Discussion Starter #7
Do you have any white smoke out of the exhaust?
215 degrees is not too hot on this platform. The bubbles in the radiator could be a problem.Is the overflow tank bubbling?
See if you can find one of those kits (sorry, I don't remember the name) that checks for exhaust in the radiator. If so, you may have a blown head gasket.
Thanks NJTB04. No smoke from exhaust, and coolant wasnt blowing into reserve tank. Tried Not to think about head gasket yesterday. :( Gonna get a new radiator cap tomorrow and see what happens. Still trying to find out what, if anything in the evap system could or would cause the lack of power.
 

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My 04Tb with 220k miles had same probs, it was a plugged up cat convertor, was just clear enough to run but was running real hot and weak....put on new cat and its like a new truck again.
 

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2008 chevy trailblazer_lt
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It is not likely an evap issue should affect power, especially if you're revving it much. When my other car cats died, the first one broke into small pieces and plugged up the 2nd cat and made power and mileage suffer and, though I didn't notice it, it was getting a quieter exhaust at the time. After changing cats, the exhaust sound came back to normal. Mileage was also going down at the time. If your problem is really that the motor gets too hot, I'd put in a new thermostat and maybe go down to the next lower temperature, and be sure to burp out any air that may cause overheating.

Rob in AZ
 

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Discussion Starter #10
My 04Tb with 220k miles had same probs, it was a plugged up cat convertor, was just clear enough to run but was running real hot and weak....put on new cat and its like a new truck again.
Thanx. I'm still hopin its not that. Got only 160k miles on it. But your symptoms sounds like mine. :( Have a great day
 

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Discussion Starter #11
My 04Tb with 220k miles had same probs, it was a plugged up cat convertor, was just clear enough to run but was running real hot and weak....put on new cat and its like a new truck again.
That symptoms sounds just like mine. Only got 160k on it, so I'm still hopin its not the cat. Thanks, and have a great day
 

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Discussion Starter #12
It is not likely an evap issue should affect power, especially if you're revving it much. When my other car cats died, the first one broke into small pieces and plugged up the 2nd cat and made power and mileage suffer and, though I didn't notice it, it was getting a quieter exhaust at the time. After changing cats, the exhaust sound came back to normal. Mileage was also going down at the time. If your problem is really that the motor gets too hot, I'd put in a new thermostat and maybe go down to the next lower temperature, and be sure to burp out any air that may cause overheating.

Rob in AZ
Thanx Rob, Just waitin for the thermostat. Parts store had to bring it in. Getting it in an hour, and praying its the cause. Have a good evening. Aloha from Hawai'i
 

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Power loss - you will need to verify fuel trim & O2 sensor readings during power loss on a scan tool. A clogged catalytic converter could cause power loss. Check w/ a back pressure gauge usually into the O2 hole. I work in a shop and realize DIY guys don’t have all the proper tools but blindly hanging parts is a waste of time and $.
 

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Power loss

Definitely is the CAT. I had this exact same issue 2 years ago... I will pulling a small trailer and about an hour into my trip, going up a hill, I lost all kinds of power; had to go into the shoulder because I couldn't go past 30 MPH. After it cooled down a bit, it was OK, but came back again once I started driving. Went to my tranny place thinking it was the trans and shop said replaced the CAT and all good.. It's been good since... Mike
 

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2006 gmc envoy_denali
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Sounds like you have some very solid advice not surprising however. Regarding the over heating, unless there is excessive back pressure from what sounds like an agreement on the CAT, the over heating could be a separate issue. Hopefully you have never mixed Dexcol with the green stuff regular antifreeze. The reaction between the two is the production of harden deposits throughout the system. Otherwise, I think the thermostat is a good suggestion. Make sure the engine side of the radiator find not crushed from previous work like from a water pump replacement. If you keep it long enough you will have to change it however, DO NOT USE ANYTHING BUT ORIGINAL AC DELCO! Otherwise, you’ll likely be doing the replacement AGAIN within a year!

Best of luck!!
 

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I had same “no power on hills” with my ‘02. It was due to a partially blocked muffler. My son had been rear-ended on a snowy road and exhaust pipe shove creased muffler.
 

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Discussion Starter #17
Thanks Guys. Parts store didn't get me the thermostat yesterday, so I'll have to wait till this afternoon for that. But I guess majority feels its the cat, and I guess that explains the low Boggin sound in engine when theres no power. Sounds like a 4 barrel that is badly adjusted and just dieng for fuel. I will let you folks know the outcome. Thanks again to all. Have a great day
 

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When I was breaking in a cam on a V-6 S-10, I swapped 2 spark plug wires but drove it that way for a half hour and then saw the glowing red hot catalytic converter. Boy did it have some major power, after hollowing that out! So, if you drive it long and fast enough in the dark, you can see if a cat is glowing if you can stop fast enough and get out and look. If it is getting *that* hot....

Rob in AZ
 

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Discussion Starter #19
Well guys, heres where I'm at...Bypassed the cat... same problem. Someone told me the rubbish from the cat could have been plugging the muffller so I removed muffler and still ran the same. When parked I gradually take rpms up to 3k with no miss at any level, and it revs without bogging. On the road...slow acceleration, crawls on the up hill and motor sounds like its a 4 barrel with a big time boggin issue. :bonk:
 
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