Fuel tank filling issues

Mooseman

Moderator
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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TollKeeper

Well-Known Member
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

Mooseman

Moderator
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?

 

Reprise

Lifetime VIP Supporter
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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Mooseman

Mooseman

Moderator
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

Lifetime VIP Supporter
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?
 
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Mooseman

Mooseman

Moderator
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.
 

MRRSM

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

Mooseman

Moderator
And the purge valve.
 

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Mooseman

Mooseman

Moderator
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.
 

MRRSM

Lifetime VIP Supporter
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

Mooseman

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

MRRSM

Lifetime VIP Supporter
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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