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2004 gmc envoy_slt
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Discussion Starter · #1 · (Edited)
(please bear with me, not sure if this should be in the OEM forum or what)

(This is on an 04 SLT, 2wd, Auto, 4.2 I6)

Ok...i've been around here lurking for a while, reading here and there so im aware of some of the issues with these vehicles. I was told it got a new battery and new plugs not long before we bought it. I cleaned the TB a while back and no issues around that time...or maybe i just didn't notice this.

  • Mine has this weird vibration. very small, yet its gotten more annoying at stop lights, i know other cars can hear this thing vibrating. it never occurs at highway speeds, only at very low speeds and when it is still. It doesn't vibrate in Neutral, only in a gear...so it can be replicated. At first thought i thought my fan blades were hitting the plastic shroud it was so loud/hard. I also thought that it was so bad my knock sensors were picking it up, but no SES light. I did have it at my buddy's shop for oil change Sunday, and we had a scanner on it to monitor a few things. My knock sensor 2 was staying out of range but we couldn't replicate the vibration this day.... weird. The required range was .8-1.0 volts and this thing was anywhere from 1.2-1.9 while the other was within range. could this be a bad motor mount and can they go bad without a lot of visual damage? we looked and only 1 was cracked in a few places, but they weren't bad from what we could tell, although when we loaded the motor with the brake on, it did move more than we'd like.

  • It has been hard to start lately(sometimes taking 4, 2-3 second turns, of the key). This meaning not the starter as it turns over fine. With the previous owner saying he replaced the plugs, my thoughts turn to fuel problem with no SES light...no misfire codes so not bad injectors. Any info on the fuel pressure regulator, or did someone recently call it something else on here...are they a common issue? i should be replacing the plugs soon since they are cheap and easy fix.

These issues listed above have been around for a little while...yesterday i came to a stoplight and held the brake (in drive) when the vibration became the worst....held it and on popped the SES light(i believe it had about 1/8h tank of gas). p0442 was the code pulled today as i needed to get fuel, but i hadnt touched my fuel cap in 9 days so its not the cap. My buddy cleared the light off, i filled up gas, drove about 15-20 miles to get my daughter and then home. i know sometimes thats not enough miles on it to set off the light again, so it may come on again tomorrow.

could the vibration be a bad fuel pressure issue or evap leak? (both causing bad mpg - im getting about 12mpg/city with a light foot)

the hard start issue makes me think theres not enough fuel pressure built up when it sits a while and thats what makes it hard to start initially...

and for giggles heres a cell pic...

 

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2004 gmc envoy_slt
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Discussion Starter · #2 ·
(bump)

well, i found where my vibration was coming from. Bad tensioner pulley.
 

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Discussion Starter · #3 ·
(bump)

well, i found where my vibration was coming from. Bad tensioner pulley.
well, that was partially it....i picked up 2mpg by replacing my tensioner pulley...same tank of gas, same route, same weather conditions....12mpg first half of the tank, 13.9-14.2mpg on the second half....still have a slight vibration though.

Does the waterpump on these go bad and cause a vibration, without showing other signs of going bad like overheating or leaky seal?

where is the best place to check fuel pressure....schrader valve? didnt see it but only looked around briefly as it was getting dark...

gonna clean the tb again and leave the battery unhooked for 45 mins when i change the plugs here pretty soon(AC Delco's).

am i talkin to myself here?
 

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2005 gmc envoy_sle_xuv
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Does the waterpump on these go bad and cause a vibration, without showing other signs of going bad like overheating or leaky seal?
YES. Usually replacing water pump and fan clutch at same time is a good idea if you have $$$.

How bad off was tensioner pulley?
 

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Discussion Starter · #5 ·
YES. Usually replacing water pump and fan clutch at same time is a good idea if you have $$$.

How bad off was tensioner pulley?
it was pulled all the way down. the best description i can give you was when we took the old one off, it was mounted parallel to the ground like "_"...when we mounted the new one, it was angled up like "/" with a lot more tension on it. Hope that makes sense. It was the "high pressure spring" inside the tensioner that had given out and had let tension off the belt.

any recommendations on testing to see if the water pump is bad? like i said, no leaks and it doesn't run hot...I'd like to at least be pretty sure that's what it is before i throw big money at it. The tensioner and plugs weren't all that much and i did/will do that myself, but im not fooling with a water pump or fan clutch.
 

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well, that was partially it....i picked up 2mpg by replacing my tensioner pulley...same tank of gas, same route, same weather conditions....12mpg first half of the tank, 13.9-14.2mpg on the second half....still have a slight vibration though.

Does the waterpump on these go bad and cause a vibration, without showing other signs of going bad like overheating or leaky seal?

where is the best place to check fuel pressure....schrader valve? didnt see it but only looked around briefly as it was getting dark...

gonna clean the tb again and leave the battery unhooked for 45 mins when i change the plugs here pretty soon(AC Delco's).

am i talkin to myself here?
Schraeder valve for fuel pressure test is at the front of the fuel tank next to the filter. (yes, under the truck) :weird:

Don't forget to check the fuel pressure regulator diaphragm for leaking by taking the vacuum hose off of it to check. Like all other regulators, NO fuel should be there in any form.
 

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Discussion Starter · #7 ·
Schraeder valve for fuel pressure test is at the front of the fuel tank next to the filter. (yes, under the truck) :weird:

Don't forget to check the fuel pressure regulator diaphragm for leaking by taking the vacuum hose off of it to check. Like all other regulators, NO fuel should be there in any form.

is there a good engine schematic online somewhere for the top end of these motors? I'd like to take a look so I'm familiar with where some of this stuff is...like that FPR/diaphragm.
 

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is there a good engine schematic online somewhere for the top end of these motors? I'd like to take a look so I'm familiar with where some of this stuff is...like that FPR/diaphragm.
I don't have access to one right now, the FPR is always on the fuel rail which is above the injectors. On the I6 IIRC it is on the driver side near cylinder 2 or 3
 

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any recommendations on testing to see if the water pump is bad?
The way I did it was grab a fin on the fan clutch and wiggle it toward the front and back of the engine. Usually if you can see the waterpump pulley shimmying with the fan clutch. Thats no good.
 

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The vibration only in gear, at idle, sounds like a bad motor mount to me, but having it get so bad at a stoplight to throw a code makes me slightly less sure on that one. I haven't had to change my own yet, but from the couple of pics other members have posted of their bad ones next to a new one, you may not be able to tell it's bad by looking at it while it's still on the truck.
 

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Discussion Starter · #12 ·
The vibration only in gear, at idle, sounds like a bad motor mount to me, but having it get so bad at a stoplight to throw a code makes me slightly less sure on that one. I haven't had to change my own yet, but from the couple of pics other members have posted of their bad ones next to a new one, you may not be able to tell it's bad by looking at it while it's still on the truck.
I'm not totally convinced its not a bad mount or mounts, but it looks more and more like they will have to be changed to see if its them. I will have more time this weekend to check the fan clutch and or water pump for play.

I'm gonna try and change the plugs, clean the TB, and check on my fuel pressure issue if i have time this weekend. It's becoming harder and harder to start after sitting for a while.

thanks Roadie.
 

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Discussion Starter · #13 ·
had to fill up with gas tonight...9 days between fill ups...210 miles on this tank. all city, lil over 12mpg...doesn't sound right again, so yeah....
 

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Yeah, I can't stand the problems these trucks are having, I am not convinced its motor mounts either, I don't want to take them out to test since even if i shake the engine that beast isnt rocking.

I just scanned a TON of parameters in hptuners, I didn't get a chance to do a ton of logs bc the battery life on this lappy sucks but ill get around to it soon enough, im sick of dumping in like 10-20 a day in gas. :-/
 

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I'm still waiting for the p0442 code to pop back up. A severely clogged cat can cause idling/vibration issues along with bad fuel economy.
 

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Discussion Starter · #16 · (Edited)
just got back from the shop and had a chance to look at it with some friends, one of which is a GM master tech.

Fan clutch is bad.

Water pump is causing (most of) the vibration, but no leaks/overheating issues. we took the tension off the belt so it ran without the accessory belt in the equation and it smoothed out a lot.

Fuel Pressure Reg is also bad. we popped the hose off and smelled gas so the diaphragm is bad. that's likely whats causing the bad gas mileage.

Fan Clutch, water pump, and new plugs getting fixed now. FPR will be here Tuesday.
 

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Where is the FPR?

And yeah I have thought about clogged cat as well, but have no idea how to diagnose that other than the sulfur smell which I am not getting. :-/
 

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Clogged cats are typically diagnosed by an exhaust backpressure test using the O2 sensor hole. Googling for that phrase, or for "testing for a bad catalytic converter" is the way I learned about that trick.
 

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Discussion Starter · #19 ·
Update

New gas cap a while back since it was so cheap.
New Water Pump
New Fan Clutch
New FPR

I dont think its the motor mounts, i've put my hands on them with it running and no signs of tears or any vibration in them. I've had someone in the car put it in gear and hold the brake while in drive, the most obvious time it vibrates is around 800-900rpm, always feels like its coming from the front end...not like from the drive shaft/tranny/rear end.

I can get through 11-12 days now without filling up and got ~240 miles to the last tank, and a few more mpg's, now around 12.7 all city driving really. But this vibration is still there and I'm pretty convinced its hampering my mpg.

I'm gonna have a friend at a shop test the evap stuff with a smoke machine only because i did get that p0442 code even though i replaced the gas cap, a hole in the evap system causing a vacuum leak is a possibility.

The other possibility I'm looking at is the fuel pump going bad, as the hard start issue still remains, like it still has to have to build fuel pressure from a bad valve or something. Occasionally while driving if i keep the rpm's constant while cruising i can feel a very slight stutter, but not enough to know if its the pump or the previously mentioned evap/vacuum leak. we shall see.

the only other thing i could see as to why my mpg is different might be the wheels, going from stockers to these 20" Boss', but that difference was minimal, and i'd expect a little difference anyways.
 

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Discussion Starter · #20 ·
Pretty sure I've just got 2 issues that combined threw me off. The hard start issue, might be a bad relief valve. The vibration it seems is coming from my transmission, but being amplified in the front end of the car. Checked the tranny fluid yesterday and it didn't smell good, wasn't the cherry red you'd like it to be, and had some grainy material in it, possibly "clutch" material. Gonna change the filter at least once and maybe twice to clean it out. The "shudder" it seems comes from the tq converter, as it feels a little loose and that's making it drive a little less efficiently.

hopefully check valve can be verified this week and filter replacement on Sunday.
 
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