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Discussion Starter · #1 · (Edited)
Hello all. I purchased a 04 Envoy 4.2L about two years ago and love it. But it needs help. This is long but I dont want to missing telling something that might be important so I'll start from the beginning. I was pulling a camper over the weekend (weight was 2600lbs, envoy totally capable of pulling it) and I was going up a steep hill and (had it in 3rd) when it started to rev up to 5000rpm (no increase of power) and held there until I put it in drive and let of the gas. Drove the rest of the way home no problem. Stopped at home then went to drop off the camper. After dropping off the camper I got back out on the main road and gave it some gas( about half throttle) and it revved up to 5000rpm (again no power) I let off the gas and felt it shift. Then it just didnt have the pep as it usaully does. When I went to get on the highway I floored it on the ramp (slight hill) and I could barely get above 40mph. As i got on the highway I could not go over 60 mph. I could tell something was really wrong and pulled over to check the tranny fluid. It was fine, oil was fine. Then my dad drove it and he thinks its the tranny. I thought it was running out of gas (it was almost on E) so I stopped to put gas in it hoping that was it. It wasnt. Then on the way home from the gas station the Service Engine Soon light came on, it drove alittle better( could go over 60mph) but had no power. I went to Advanced to get the code read and it came back with: P0172 System Too Rich (Bank1). I had a similar code with my Jetta and it was the MAF Sensor.

Update: I had a mechanic check it and hes says that all sensors are performing correctly. Hes still looking into it. Does anybody have any ideas what it could be?
 

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If it reved up without going anywhere thats definately a transmission problem.
Sounds like its starting to slip. The Service Engine Light may have just been a coincidence. Automatics can be tricky to diagnose at times, the sensors arent designed to catch certain issues their prone to. I'd probably get the transmission pressure flushed and a filter chang at the very least. You may have overheated the fluid. But I'd think thats the first thing the mechanic would check.
For the future if you tow a lot with this truck I'd look at a auxilary transmission fluid cooler, autos like the fluid cool (to a certain point) and when towing you can almost never get the fluid cool enough.
 

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Discussion Starter · #4 · (Edited)
If it reved up without going anywhere thats definately a transmission problem.

It moved, it just didnt have any power. Kinda like the brake was being applied at the same time as the gas.
 

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My 2003 TB had to have some PCM updates and an 02 sensor changed. Mine was acting weird til this work was complete.(Including stalling, shuttering and horrible shift points) I would have dealership take a look at it again. PCM controls everything from shifting to fuel regulation.
 

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It moved, it just didnt have any power. Kinda like the brake was being applied at the same time as the gas.
What I meant by that was an increase in RPM's but the truck not speeding up indicates the transmission was slipping.
An automatic transmission is basically a large hydraulic pump. The pump recieves power to turn from the engine via the crankshaft and input shaft. The faster the pump turns the more hydraulic fluid (transmission fluid) is forced into the variable drive vanes. When the drive vains reach certain predetermined RPMs the transmission will shift the. On your truck this shift is not occuring, possible reasons why are as I said possibly the transmission is slipping and not allowing the truck to speed up, this could be the variable vanes not changing angle or a drive slip, or as was also pointed out the transmission may not be recieving a signal allowing it to shift or change the angle on the variable vanes, in effect locking it out from a higher gear.
 

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Discussion Starter · #7 · (Edited)
update.

When I just got the Envoy back from my mechanic. He wasnt able to figure out the problem w/o charging me labor. He clear the PCM memory and the air/fuel mixture is back where it should be. He said after doing some research he found that my engine is known for PCM update problems. But I dont have the funds to spend $90 on getting that done if it doesnt sovle the problem. I noticed that in park it doesnt want to rev up if i give it gas. Im no mechanic but I would think then its not the tranny. The mechanic at the dealership where I bought it said to disconnect the cat and see if the power returns. So I will be doing that tonight. Let you know.
 

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He said after doing some research he found that my engine is known for PCM update problems. The mechanic at the dealership where I bought it said to disconnect the cat and see if the power returns.
I'm still going with PCM update! :) Good luck disconnecting Cat, If the exhaust is original its all one piece exhaust! :no: I think the mechanic is drinking his own bath water...:whistle: IMO
 

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Discussion Starter · #9 ·
Update

So I disconnected the cat and took it for a spin around the block. YEAH I GOT POWER! It ran great! It shifted fine had the pep it used too. So that makes me 90% sure thats the problem. Now the trickis finding one! There hard to find!! Let you know when I find one and put it on.
 

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So I disconnected the cat and took it for a spin around the block. YEAH I GOT POWER! It ran great! It shifted fine had the pep it used too. So that makes me 90% sure thats the problem. Now the trickis finding one! There hard to find!! Let you know when I find one and put it on.
Nice! Where did you disconnect it? Mines a 2003 and Mine was all one piece? I was just under it yesterday on hoist.

Well I was foiled again....Sorry 'bout that. So Now that you have a plugged cat, it would take us to Why? Why is a Cat plugged on a 2004, with that many miles. Anybody finding this a bit odd or is it just me.
 

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Discussion Starter · #11 · (Edited)
Nice! Where did you disconnect it? Mines a 2003 and Mine was all one piece? I was just under it yesterday on hoist.
On mine if you get under it and follow the pipe to the exhaust manifold the was 3 bolts. Or if you look thru the passager side wheel well move the flap on the left side of the wheel you should be looking right at it. Im not sure why it would be clogged. I noticed a decrease in performance and could tell something wasn't right for awhile before I pulled the camper. Maybe going up the hill just did it in.
Does anybody think I am wrong in thinking its a clogged Cat? I mean it run good with it disconnected. How many miles should a cat last for? I have 90k on my envoy.
 

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There's no set life span for a cat, some go earlier than others. If it was getting bad running up a hill with a load didnt cause it to go bad it showed you the problem exsisted, the PCM couldnt compensate to off set the affects anymore.
With it disconnected it wont run good for long, as soon as the PCM starts adjusting itself you'll have an engine light and it'll start running different.
 

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Discussion Starter · #13 ·
There's no set life span for a cat, some go earlier than others. If it was getting bad running up a hill with a load didnt cause it to go bad it showed you the problem exsisted, the PCM couldnt compensate to off set the affects anymore.
With it disconnected it wont run good for long, as soon as the PCM starts adjusting itself you'll have an engine light and it'll start running different.
So are you saying that it might not be the cat? Or are you saying that something else is wrong and caused the cat to go bad?
 

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No it could be the catalytic converter. But you should get codes to confirm this. And if it is the catalytic converter check for codes after it's repaired to ensure things are operating correctly. There are many reasons a catalytic converter will burn out or clog up. It could be problems related to how the engine is running, how the vehicle is driven, or it could be a "natural death" for that particular catalytic converter. Catalytic convertors have been known to go as early as 70k on a good running car and last past 200k on a bad running car. While there are some tuning tips and driving styles that make them last longer 90k isnt really early for one to go.
 

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Discussion Starter · #15 ·
Well I got a universal cat put on today and it runs great!! I went with a universal because it only cost $130 (installed) versus the $468 the dealer wanted for an OEM. He said it was definently clogged. all the combs in the front were melted. Now the question is why was the engine dumping soo much fuel? There is currently no check engine light. I am going to get the PCM update done in a couple of weeks. Hopefully that will take care of everything. Thank you to all that helped me and gave me advice! Much appreciated!!
 

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wasnt the cat still under warranty? it is a 2004 is it not? and well, a similar story to this of mine is i had the same problem, push the gas, rpms increase, speed barely increases, only when it was cold though. was in the dealer 3 times, a week each time, and finally they figured out the whole problem, the valve body!
 

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Discussion Starter · #17 ·
wasnt the cat still under warranty? it is a 2004 is it not? QUOTE]

no the warranty expired. I bought it used with a 3yr/30k warranty. I was told the factory warranty didnt transfer.

The valve body you say. That might explain why it was dumping so much fuel. i'll have to look into that.
 

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wasnt the cat still under warranty? it is a 2004 is it not? QUOTE]

no the warranty expired. I bought it used with a 3yr/30k warranty. I was told the factory warranty didnt transfer.

The valve body you say. That might explain why it was dumping so much fuel. i'll have to look into that.
The factory warranty may not transfer, but the emissions warranty automatically transfers with any vehicle still under the mileage or time limits. Emissions waranty is a federal regulation that the dealer must honor.
But you may have been out of mileage limits for it.
 

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Discussion Starter · #19 ·
Still got a problem!

Well everything was good for about the first 60 miles or so. But the Service Engine Soon light came on again. I got it read at Advance Auto Parts and it was a P0420. Cat thresholh too low. I thought maybe that I got a faulty cat. but when I took it back to the place that installed it, he put a new one on but said that the first one was good. Any ideas??
 

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In some cases I have had, it has been the MAF sensor. If you have a K&N filter or any filter in which you spray an oil on it, it can cause the MAF to fail. I had a 2004 Land Rover Discovery do that to me a few days ago. I checked all the wires the tranny etc... all in all it was two and a half hours of searching to find out it had a bad MAF and 2 bad O2 Sensors. It is possible you have a tranny issue especially if it was hat and the tranny was working hard but you wouldn't trip the CEL light with the code you got.
 
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