Engine trouble on 04 Envoy

**spirentc** · 06-22-2007, 04:34 PM

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?

**tbplus10** · 06-23-2007, 11:39 AM

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.

**Steve** · 06-23-2007, 12:12 PM

There are known issues with the Trailblazer / Envoy transmission.

I can be anything from the sunshade to a sticking shifting solinoid. I've experienced the same problem with shifting between 1st and 2nd in my 2002 Trailblazer.

http://www.gmtruckclub.com/forum/sho...t=transmission

http://www.gmtruckclub.com/forum/sho...t=transmission

**spirentc** · 06-23-2007, 02:20 PM

Originally Posted by tbplus10

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.

**Cableguy** · 06-24-2007, 10:20 AM

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.

**tbplus10** · 06-24-2007, 01:43 PM

Originally Posted by spirentc

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.

**spirentc** · 06-29-2007, 03:50 PM

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.

**Cableguy** · 06-29-2007, 05:20 PM

Originally Posted by spirentc

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!

I think the mechanic is drinking his own bath water...

IMO

**spirentc** · 06-29-2007, 08:42 PM

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.

**Cableguy** · 06-30-2007, 12:49 AM

Originally Posted by spirentc

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.