Fuel tank filling issues

Mooseman

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Dec 4, 2011
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Ottawa, ON
You might have seen my posts in the WDYDTYGMTT? thread but I will recap. My 08 Avalanche with the 6.0L has had issues with fuelling since I bought it. It's wasn't the usual slow fuelling issue where the pump just clicks off all the time but it pukes fuel out after clicking off once full.


What I've done so far:

- Replaced the vent solenoid and filter as per the attached TSB
- Checked the filler vent hose. It had a bronze venturi that had a small pin sized hole. Removed that and checked the hose itself for blockage by blowing compressed air to the tank. Although the air went in, I could hear some gurgling in there.
(Went for a test fill, still puked the exact same way)
- Replaced the charcoal canister.

It needed 1/8 of a tank and when I tried to fill it full speed, it clicked off right away and puked gas. Tried to fill slowly, clicked off and puked. Only got 1/16 of the tank in, not even full.

So now, after replacing the charcoal canister, it's worse with both slow filling and puking problems. I'm at a complete loss. I don't like the idea of dropping this big ass tank and will take me forever to drive it to empty since I'm not driving so much during this pandemic. And even then, what do I look for?

I need help from the collective on this one.
 

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  • Evap Vent TSB.pdf
    2.4 MB · Views: 12

Chemman

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Jul 13, 2013
35
Maryland
Just for kicks, try removing the hose from the purge valve solenoid before your next fill up and see if that helps any.
 
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TollKeeper

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I saw a episode on SMA just recently, he was working on a FS-GMT, where he replaced the purge solenoid or vapor or something, and that hose he did NOT connect. As the new one he got from a Impala, and they dont have them. It supposed to prevent some problems, and causes no check engine lights. The part is also 1/4-1/3 the price. Just an fyi in case you need it.
 
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Mooseman

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Ottawa, ON
Here's another bit of info. Looked at the old canister and it had raw fuel in it. So something is allowing liquid fuel into the canister. Looks more and more like a tank drop is in my future :frown: . I'm gonna have to see if there is a valve on the tank and if it's replaceable.

Here's a question. Anybody know if any of the three lines on the fuel pump module goes to the evap canister?

19368772_Alternate3__ra_p.jpg
 

Reprise

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I just put the Sierra in the garage tonight to R&R my fuel pump tomorrow; I'll trace out what I have and let you know. I don't think (?) it does... the evap is supposed to return the raw fuel to the tank, the way I understand it. But maybe it does it via a line on the fuel pump (which sits in the tank, as we all know). Also, since mine is an '03, it's a 'return' system, where you '08 is returnless. But I'll let you know what I find out.

The TSB you posted is a reroute for the lines, to eliminate drainage into the canister (factory put the lines above the canister; the TSB reroutes them to be lower than the canister). So it may be a design issue you have, and not a parts failure (only as far as the fuel in the canister; I don't know the solution for your existing tank fill problem, since you've replaced the canister already, which is where I'd start, given my own experience 'rejuvenating' my own a few months ago).
 
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Chemman

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Jul 13, 2013
35
Maryland
Mooseman, it does appear that one of the lines from the fuel pump does go to the vapor canister. I found these which may be of help. They are supposed to be valid for the 6.0 engine.
 

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  • 08 Avalanche Emissions.pdf
    161 KB · Views: 5
  • 08 Avalanche Fuel Line Routing.pdf
    112.9 KB · Views: 5
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Mooseman

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Ottawa, ON
Those docs help a lot. Thanks. So there are multiple points for the vapour return to the canister. I wonder if one of the two circled valves are defective as well as the one on the pump allowing raw fuel into the canister.

Tank vents.jpg

Those are normally non-replaceable but someone had replaced one on his TB.
How to replace non-replaceable tank vent valve
 

mrrsm

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Would the Fuel Vapors collect and condense inside the Vapor In-out lines if the Extra Vapors were not able to reach and get ingested into the Engine during Start-Ups due to a Failed Evap Purge Valve on the Motor? Actually... I should have asked this first ...IS there an Evap Purge Valve mounted on or near the 6.0L Engine at all?
 

Mooseman

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Dec 4, 2011
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Ottawa, ON
IS there an Evap Purge Valve mounted on or near the 6.0L Engine at all?

There is, like all of them. Maybe I should replace that too while I'm throwing parts at it. Easy enough to replace and can check the line for blockage or raw fuel.

I don't think fuel vapour can condense into liquid form like water can.
 
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mrrsm

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Upon reflection... With 1 Gallon of Gasoline vaporizing into 160 Gallons of Fuel Vapor at Ambient Temperatures... I think you're right.
 

Mooseman

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Ottawa, ON
And the purge valve.
 

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  • Purge valve.pdf
    311.2 KB · Views: 12
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Mooseman

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Doing some YT surfing, especially on the SMA channel, found this one that has gas in the canister that explains that it's the fuel pump. So I guess I'm on the right track for what I was assuming about that valve on the fuel pump.


I'm just not wanting to drop that tank. Thinking of cutting a hole in the floor.


And I have a feeling this will not be the only time I'll need to do this so might as well do it.
 
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mrrsm

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You have already though of these ideas... But for anyone else considering doing this work through the Floor Board... THIS Tool will Cut through Thin Gauge Steel like Butter... Safer and More Controllable than using anything in the style of Sparking Cutting Wheel:

Neiko Pneumatic Tin Snips:


NEIKOAIRTINSNIPS.jpg

Choices for Replacement Aluminum Plate Panels (Shape it FIRST... Then Cut out the Floor Board):


Choices for High Temp Sealant-Caulking:
:

Choices for Rivet Gun and Rivets Kits:


If it comes down to needing it... Choices of Metal Working-Shaping Hammer & Block Sets:

 
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Mooseman

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It's an idea however apparently they are not good for cutting over ribs. Also looking at nibblers.
 
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mrrsm

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Right... But still very handy for cutting 'T" Shaped Aluminum Tabs from the Work Piece that can be arrayed around the perimeter of the OEM Floorboard Piece and then installed using a combination of some High Temp JB-Weld and Large, Steel Pop Rivets. :>)
 
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Mooseman

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Dec 4, 2011
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Ottawa, ON
Yesterday, I went to fill it when it had 1/4 tank left and it was able to take it at full speed. However, when it clicked off, it puked a bunch of gas out. So I'm back to my original problem.

Doing some more searches, I think I may have found what's really causing it.


...
The dealer was able to duplicate the problem but had to call GM because they were stumped. They checked all lines and evaporative emission lines and they were all fine. They said there was raw fuel in the canister.

The primary problem was a "rollover valve" in the fuel tank stuck open. I assume this stops fuel from coming out of the filler if the truck flips. Also, it sounds like it is in the tank itself so it is not serviceable short of replacing the tank.

So this sounds like my problem exactly. Raw fuel in the canister is likely because the tank gets overfilled without that valve working and fuel gets pushed into it. Another poster said that when he removed his rollover valve, he wound up with this problem. So apart from rollovers, it also likely shuts off the filler inlet when it's full.

So looks like a tank replacement is in my future. No way I'm paying $850 for a new one and one from the U-Pull would not be good since they drill them to drain them unless I plastic weld it, which I've successfully done on my snowmobile tank. Another option is the fix for EXT's that had the original cracked tank problem but even that is over $200CAD.

I could also just buy a used tank from a yard already pulled. This particular problem is not very common so odds that another tank would have the same problem is low.
 
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Reprise

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FYI - I just looked on car-part for your tank - it looks like they're available all over (near me, even), for $100 USD or less (correct for a 6.0 Avalanche, but come from various other similar-gen / platform vehicles, like Escalades.)

If you can stand on one side of the border gate, I'll throw one over to you? :dielaugh:


Also... I had promised to trace out the outlets on my pump when I took it out, earlier in this thread.

You probably don't still need the info, but I checked the pump when I took it out today.

Mine has 3 line connections (and two one electrical). It's also a Carter (and looked almost new, TBH, especially the filter sock.)

(on edit: Figured out that PO (previous owner) put the wrong pump in mine - there's a second connector for a pressure switch that wasn't connected -- as it turns out, mine doesn't have the corresponding 3-pin harness to plug into it (and if I did, I should have been getting CELs / codes, which I haven't been)

I noticed there were letters on the top of the outlet fittings, marked 'F', 'A' and 'R' (no jokes about how a Carter pump won't actually get you very far, ok? lol)

The leftmost one is 'F', and that has to be Fuel, because that one by far had the most fuel come out of the line, when I removed it (and I did depressurize the lines, beforehand, plus my check valve is shot). It's the largest of the three, btw.

The rightmost one is 'R', and that has to be 'Return' (to tank), as a tiny bit of fuel came out of it, as well.

In addition, the left and right lines have the special (white) retaining clips to push inward / disengage before squeezing the line connector tab.

That leaves the one in the middle, which was marked 'A'. That's the 'vapor' connection. This line has no special clip (only the tabs on the line connector that you squeeze -- it's different than the other two, in that regard.) Dunno what the 'A' stands for - can't be 'atmosphere'.

Like I said... you prolly don't need this any longer, but I promised the info. As for why it took me as long as it did to get to this... that'll be in my writeup, when I'm done. Currently trying to mod the 'bucket' of the module to accommodate the replacement pump. Now exchanging the one I bought for a different one, and returning the one I bought.

Sneak peek - doing the 'bed tip' isn't worth it, in my book. Next time (if there is one), I'll definitely drop the tank (I may need to do that to get the new pump in, anyway).
 
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Mooseman

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Dec 4, 2011
25,262
Ottawa, ON
Finding a tank won't be an issue. They're the same as Suburbans and Tahoes through multiple years. From the dealer:

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Chevrolet Suburban 1500 5.3L Vortec V8 FLEX A/T 4WD LS Sport Utility 2004, 2008, 2009
Chevrolet Suburban 1500 5.3L Vortec V8 FLEX A/T 4WD LT Sport Utility 2004, 2008, 2009
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So fairly common. I wanted to get one myself at the U-Pull so that I can inspect the rollover valve and see if I could be lucky to find one with a recent pump and get all the hoses with it. Just in my local U-Pull yard, I count compatible 3 Avalanches and 2 Escalades but oddly, no Suburbans. I was going to get one this week and possibly replace it however my recent health issues and the weather are now hampering those efforts so this will be delayed until the spring unless I'm forced to.
 
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Reprise

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Yeah, I was thinking 'cost' and 'not drilled', vs. raw availability.

Given the current situation, l'd let it wait, too.
 

Mooseman

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Dec 4, 2011
25,262
Ottawa, ON
Just realized that I never updated this thread with the solution on this issue.

So a lot of research told me it was the overfill/rollover valve in the tank inlet. It isn't replaceable by itself. Got another used tank and replaced it earlier this spring. Confirmed that the valve was broken and fell in the tank. After replacing the tank, it's been working fine.

Here's what was happening before replacing the tank (video):

And after (video):


If you haven't started looking into this yet, you will likely need to also replace the charcoal canister because as the tank would get overfilled, this didn't allow for that air space at the top of the tank and raw fuel would get pushed into it. When I saw the fuel in the canister, that pretty much confirmed my suspicions about the broken valve in the tank.
 

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