Hey Vortec Guys! / Sierra pickup / Suburban / Yukon etc - Finally has Index!

[rayra]

Discussion on potential transfer case wear-thru issues -
http://forum.expeditionportal.com/t...an-A-2002-2500-Suburban?p=2312185#post2312185

seems a steel bracket floating in an aluminum casing can become a Badness Thing. And your GMT800 k-series almost certainly has the affected models of transfer case. Looking to nail down the particulars, right now it seems like a very high mileage or hard use / abuse issue.

eta and a topic on it
http://forum.expeditionportal.com/threads/172888-PSA-GM-Fullsize-4x4—Be-Aware-of-T-Case-Pump-Rub

 

[rayra]

Question for the GMT800 mafia - ever have or heard of early cutoff trouble when filling your tank? At least 3x in recent weeks (that we're aware of), we've 'filled up' our Tahoe from near empty and only later noticed that the auto-cutoff has resulted in a partially filled tank. I think it's the amount of vapor being generated and triggering the cutoff. But nothing has changed on the vehicle that I'm aware of that would suddenly start causing this to occur. The missus' bad habit of driving until the fuel warning light comes on certainly isn't new. And she reports it happened again recently when she actually went to fill the tank when she got down to 1/4.
And even as I type this out I begin to wonder about the fuel vapor cannister. 180k mi never changed.
Just starting to dig for answers on this, was wondering if anyone here had encountered some similar trouble or might know the solution.

 

[rayra]

first approximation / guesstimate, after digging around online. Probably a sticking or failing evap vent valve solenoid. Possibly in combination with some stations having their vapor shutoffs set differently. Lack of vent flow, buildup of fuel vapors, early shut off of station pump.
Looks like a $15 part (Rockauto, Vatozone wants $29) and some grit in the eyes digging around under the vehicle to make the swap.

Still digging around for more definitive answers / explanations.

Have to wait for this evening to pull any codes. No CEL as of yet.

 

[Burb One]

Question for the GMT800 mafia - ever have or heard of early cutoff trouble when filling your tank? At least 3x in recent weeks (that we're aware of), we've 'filled up' our Tahoe from near empty and only later noticed that the auto-cutoff has resulted in a partially filled tank. I think it's the amount of vapor being generated and triggering the cutoff. But nothing has changed on the vehicle that I'm aware of that would suddenly start causing this to occur. The missus' bad habit of driving until the fuel warning light comes on certainly isn't new. And she reports it happened again recently when she actually went to fill the tank when she got down to 1/4.
And even as I type this out I begin to wonder about the fuel vapor cannister. 180k mi never changed.
Just starting to dig for answers on this, was wondering if anyone here had encountered some similar trouble or might know the solution.

Yep, they all do that. It's the charcoal canister or the solenoid. The solenoid is cheap (replace first). If that doesn't work, then try "blowing out" the charcoal canister with a compressor. If that does not work, it's a $120 replacement for the canister. There's ton's of videos on youtube, both are located right forward of the rear axle.

Was very annoying until I fixed it with the air compressor. It will start getting worse and worse until it's every ten seconds while filling. Most of it is caused by overfilling the tank, where the overflow fuel gunks up the charcoal canister. I blew mine out a year ago (not replaced), and it's slowly coming back. I'm thinking it might be a $100 every 16 year issue to just replace it. Figure when it goes bad, it takes me an extra 5 minutes every time I fill it up. The time wasted at the pump is worth it.

 

[XJLI]

Yup. Common problem. I blew my canister out with air and the issue went away, replaced the EVAP solenoid on the intake manifold for a CEL and still had one for the solenoid at the fuel tank (which was already relocated previously due to a TSB), so I bought new hose and a new solenoid but the CEL went away before I could put the parts in. Haven't had an issue for 2 months? Don't top off the tank when it is working normally... when the pump clicks off stop filling.

 

[Martinjmpr]

I have noticed the last few fillups I'll fill the tank and the needle isn't quite on "F." I normally let the pump click off twice before I stop.
.
Where is the filter/solenoid located? Any YouTube videos on replacing it?

 

[rayra]

On the Sub the charcoal vapor cannister is is a boxy thing near the front inboard corner of the fuel tank. The vent valve / solenoid is right there as well. And there's the evap purge valve / solenoid up front, IIRC it's on the top of the intake manifold, small black fixture with a bright green disc on top. It all looks pretty easy to get to. The Tahoe's seems to be more central, a little further inboard of the tank.
I'm going to go ahead and order to vent solenoid and go from there. I went ahead an plugged my blue tooth OBD port reader and android tablet / Torque app setup into the Tahoe last night and no logged codes. Whatever is going on it isn't a complete failure of either wired solenoid.
And a caution, there's some thin-walled large diameter (3/8"?) plastic tubing involved. Might be fragile. Can be readily patched with rubber vacuum hose. And if you crack it you'll wind up with some fault codes later on.

Along the way last night I also found mention of overfilling leading to breakdown of the charcoal filler in the cannister and some charcoal grit backflowing into the lines and possibly fouling the vent valve. It might be sticking or binding intermittently. We aren't having this problem at every fill, so that seems like a symptom match. The process of getting things apart, inspecting the valve, clearing the lines etc is the same work to replace the valve. So I'm going to get the valve first anyway, do all the cleanout and install the new one. At 180k+ mi. it seems like a worthwhile thing to do. Part's only $15-20.


/"I've just picked up a fault in the AE-35 Unit. Its going to go 100 percent failure within 72 hours."

 

[Martinjmpr]

Awesome, post pics or a video when you're done, I think I'd like to do this just as a part of preventive maintenance.

 

[boll_rig]

Same actually. Feel like this one has to get me sooner rather than later. Surprised it hasn't got me yet. Great info.

 

[rayra]

This vid is '04 avalanche, but it's pretty much the same generally. And he does a decent job explaining it.

https://www.youtube.com/watch?time_continue=173&v=4QSjkWgBsjE


best I can understand it right now is that the vent valve acts like a snorkel ball. Key off, it's supposed to be open. When you fill your tank, the vapors go out a top vent pipe on the fuel pump fixture and into the charcoal / evap cannister adn thru it to the vent valve. The charcoal is supposed to capture the VOCs. This arrangement vents pressure buildup as you fill your tank. Eventually you get enough fuel vapor concentration to trigger the pump to turn off. Vent valve fails or sticks closed, no pressure relief, the pump shuts off sooner / partial fill.

The purge valve / solenoid sits on the intake manifold, piped to the evap charcoal cannister. With key on, the vent solenoid is commanded to close. Periodically while the engine is running, both the purge and vent valves are commanded to open and the engine sucks in vapors out of the cannister (air flowing IN thru the vent valve). 'self-cleaning' cannister.

Overflow your tank too often by topping off - or maybe sloshing fuel around too much while offroading - and you get a surge of fluid down the vapor pipe, saturating the charcoal cannister. This can cause a breakdown of the charcoal and result in free grit which can foul either valve.
So plan during a valve change to open those lines and blow them clear (and NOT into the valves or back in the cannister).
Loose grit is definitive for changing the evap / charcoal cannister.
A sticking of failed-closed vent valve / solenoid or otherwise clogged or blocked cannister will result in the early gas station pump cutoff.
A test for a failed vent valve - and an emergency temp fix if you are far from home and can't readily fill your tank - is disconnect the vent hose from the vent valve. Open it to the atmosphere. If it's just the vent valve, you can pump normally. The other 'emergency fix' is just pump your gas into a fuel jug and then pour it in your tank. It'll be faster than sitting there clicking the pump handle continuously.

I'll post some pics in a few days, when I work on the Tahoe, and maybe sooner on the locations on both Sub and Tahoe, if I do some scouting beforehand.

Parts look very similar and Delco replacement parts list as substitutes for several part numbers. But there are several different parts for this vent valve, within the GMT800 series vehicles. And their locations are varied.

more to come on this. If you do your own, please post some notes or pics of where yours are located and what you found in terms of fault, grit etc.

Right now we're not getting any warning light or logged faults, but the problem seems to be rapidly getting worse. My guesstimate is that the vent valve is sticking or fouled. Fortunately the missus is flying out of town for a while and I'll be able to fix it without any rush, sometime next week..

 

[fl0w3n]

Funny, I had a CEL just the other day saying the charcoal canister was having an issue, and I didn't put two and two together that the extremely obnoxious issue of the fuel pump tripping every second was because of this as well.

 

[fl0w3n]

Alright, so...

I decided to get the charcoal canister out today and blow it out to see if it'd help.


Of all the things I've ever done to a vehicle, that was probably one of most infuriating extractions of a part, ever.

Gas tank skid is made out of fiberglass, found that out the hard way after I was having those tiny fiberglass pains in my fore arms.

The three hose fittings have a ridiculously difficult release on them.

The location of the transfer case, frame rail, drive shaft, torsion bar cross member, and additional frame cross member made getting my hands up there to even attempt decoupling the hoses a nightmare.

There's two of those ribbed push pin hose clip things (kinda like the body fender clips, but the ribbed kind) on the top of the canister... yeah I just cut those off with Dikes.

Add to that all the dirt falling directly into my face because I needed my face under it to see what I was doing... after what felt like an hour of fumbling with it I finally got it free.

Then guess what? Doesn't fit out of the space once it's free. I wound up having to put a jack under the transfer case and tweak it way up toward the floor pan to get the driveshaft to allow enough clearance between it and the cross member so the canister could wedge out.

Blew it out for a while, bashed it/shook it around, blew it more, reinstalled it... marginal if any difference at all at the pump. Looks like I'm spending $100 on a new one, because I can't handle filling 35+ gallons while standing at the pump resetting it every minute or so.

 

[rayra]

wait, if air goes in one pipe hole on the cannister and comes out the other at comparable volume, the problem shouldn't be the cannister. It's more likely the vent valve itself. If you reconnect the cannister and levea the valve disconnected and go get gas, you can test that. But that doesn't much matter after all that work to get the old one out it doesn't make much sense to put it back in, unless money is really tight.

 

[fl0w3n]

Yeah I kind of figured the same, that the canister wasn't really the issue. I did a little more research last night and the p0446 code I was getting is more likely the valve like you said.

I'll attempt to clean the valve after work today.

I wasn't sure what would happen if I just left the canister out or not hooked up. I need the truck for a trip this Friday, I don't think I can get a new canister in time before I leave.

 

[Hillbilly Heaven]

Curious with this talk about the charcoal canister and valve. I wonder if they use the pressure sensor on the fuel pump module to read pressure in the tank to actuate the valve. I know the pressure sensor is used to detect the gas cap being forgotten.