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

[rayra]

You're prepared to flush it, I don't think it matters much which path you take. There's no harm that I know of, going from Dex to universal. IIRC the only trouble is introducing dex to vehicles whose fittings aren't made to cope with it. But I'm not even 100% sure about that. One of these days before the summer is out I'm doing a refresh on my cooling system (finally), already got the gallons of dex sitting around waiting. I didn't think it was important enough to switch. And have dex in the Tahoe too. Having two GMT800s cuts both ways. Common spares, but anything I change I have to do both to maintain the desired commonality.

Had to abandon my plans for trying to drive to Idaho for the eclipse, so my impetus to do any upgrade work on the Sub has petered out for now. And still have to solve the gas pumping issue on the Tahoe. As it stands right now I'm thinking the rollover float / valve in the fuel pump assembly is stuck closed. Going to try and dislodge that with air pressure up the vent line. And pull the filler neck to check for any obstructions there. If I don't get that fixed soon the missus might just decide to get a new vehicle. And there goes my fiendishly clever plan to have two GMT800s.

 

[Hillbilly Heaven]

Raya I haven't researched your fueling problems other than reading your adventures in curing it. I noticed today while fueling my Silverado that it vents thru the filler neck. I know you mentioned in your state you have those silly vapor capture hoses that go over the filler neck. Luckily we don't have them here. Having not researched this and this is based on my knowledge of F brand vehicles they used a hose inside a hose system in the filler neck. The normal 2 inch or so hose was used for fueling vent. The inner hose was same size as nozzle. This was before ethanol was allowed to be blended. When ethanol showed up at the pump, they were having the same fueling problems of constantly kicking the pump off. Problem was the ethanol softened the inner hose causing it to collapse. Only cure was to buy a new filler neck as the fueling hose was made inside the filler neck.

Just looked up the filler neck for my Suburban and Silverado both 2000 models and the Silverado does use a hose inside a hose but the Suburban uses a separate fueling vent hose that runs along the outside of the filler neck.
http://www.fillernecksupply.com/

 

[rayra]

They're separate hoses on the GMT800. Separate but adjacent attachments on the tank, they come together at the fuel filler opening, along with a singing gate that's meant to interfere with siphoning attempts. I meant ot pull that all apart this morning but did other things in the few cooler hours. And I've got a carpet cleaner coming first thing in the morning tomorrow.
Ethanol could very well be an issue. I'm just not going to know until I pull them off.

My plan of attack right now is to pull the vent line off the vent valve solenoid - easiest line to access with the air hose -and turn the key on to close the purge valve. That should leave the compressed air nowhere to go but back up the cannister to tank line, which leads to the rollover float / valve. Going to try slow air flow and pop it a few times.
If it is not obstructed, air should flow thru and out the filler connection. But I have to verify those are clear, first.
Got to be something screwed up, as it even kicks the pump off when I'm compressing the boot on the pump nozzle and holding it away from the filler neck. Even then I get such heavy fumes flowing back that it trips the gas pump. Part of what makes my think that rollover vent valve is stuck closed. The missus had the habit of giving the pump an extra goose after the first / proper shutoff. 180k mi of over-filling - and the natural operation of the Purge system, that would tend to suck that rollover shut, too - seems to have bollixed thing up. Too, given that purge valve operation, it's probably a fool's errand to even try the air line blow. Even if I free it, the first random operation of the purge valve will probably jam it right up again.
And it's such a PITA operation to drop the tank and pull the pump, that it's not even worth doing so to inspect it. Might as well plan on doing a fuel pump replacement. Once I pull those filler lines, there isn't anything else it could be.

Another test might be to pump air in the filler and see if it comes out the vent valve. That is open at rest / key off and is only commanded closed when the purge valve is commanded open. I can wrap my air nozzle in a rag or otherwise seal it to the filler and have the missus blast air in while I get my hand on the vent. This test right now should fail, if it isn't mostly a blockage in the filler.
eta I'm going to go try that test right now. IF air comes out the vent valve solenoid then that leaves the filler neck as the likely culprit.

 

[rayra]

Diagnostic success.

Rigged up a handball as fuel filler plug and had the missus pump air thru it, while I reached up around the cap of the vent valve solenoid. No air felt or heard. Watched the plastic gas tank swell and then release slightly as air flow was maintained. Got a whiff of gas vapor wafting up the driveway.

Key ON to shut the purge valve, repeat test, tank swells more, until sounds of air escaping are heard and air out equalized with air in. Still nothing noticeable out the vent cap.

Pulled line from evac to vent valve off of vent valve, key ON, blew air in that line, hoping / expecting rollover vent valve to open, which it eventually seemed to. Initially no air felt escaping out fuel filler. Second attempt there was.

Switched ends, again air pumped into tank via filler, strong air flow out the still disconnected vent pipe. Success!

Reconnected vent line, Key ON, air in filler, air out the vent valve. Proper function.

But it's not a fix. All I've apparently done is dislodged the closed rollover valve / float. I've been unable to determine the frequency of the purge valve operation. At startup? during heavy load on the engine? every 100mi? no idea. My suspicion is that the first time the Purge valve open / vent valve closes, as part of an emmissions control cycle, it's going to suck that faulty rollover valve shut once more. And that it will stick there.

About the only way to be 100% sure of things right now is deliberately disconnect the vent valve hose again, open the system such that a Purge cycle doesn't get any suction on the rollover valve, and start the thing up and go try and fill the tank. And if it fills without early cutoff I'd say I've nailed down the problem. I think I'll do that now, as confirmation. The vehicle will throw an evap code for the open line, the first time the Purge kicks, I presume. And I'll guess I'll find out if that happens at startup, too.


I'd have to do 100% the work to change the fuel pump, just to pull the existing pump assemblage and fiddle around with the rollover valve. I could probably make it work again. Images and diagrams of similar devices show its much like a toilet float valve. But not even sure if it's a serviceable unit. Cannot find any replacement part available, GM dealer says 'whole fuel pump assemblage', $475. And over $1k for them to do it. Rockauto has Delphi OEM part $209. And Delco with all the bells and whistles for $224. And the fun of dropping the fuel tank in my driveway. I can readily do it, just not going to be any fun.

pictures and diagram to follow

 

[rayra]

Success filling the tank without a stoppage. ~21gal without interruption. So I think I've got the real world matching my diagnostic logic.

Also did not get a CEL, so that means the Purge valve doesn't open on (every) Start. My guess is it's under heavy load / acceleration only, when the intake vacuum is highest for best draw on the canister.

Looking at images of pumps at rockauto, I see no evidence of a rollover valve structure. Looks like the vent pipe is a straight-thru tube. Maybe that's a manufacturer 'fix'.

I've put the vent line back onto the vent valve solenoid, system is back intact. Told the missus that I don't expect the next fill up to work without interruption. Told her to look at her trip mileage, do some rough math dividing by 14 so she'll have a rough idea of how much gas should go in. So when the gas pump cuts off she'll know if it's early or about right. And won't keep trying to pump gas in if it's close to full.
And that the perma-fix is basically a new fuel pump, when we can arrange it.

A crude diagram of the evap / fuel tank system

The quick stopper I made for pumping air into the filler. Handball with 1/4" hole on the air nozzle side, a 1/2" hole opposing and all the debris blown out. Just jam the nozzle / ball combo against the filler opening.

In all the digging around the internet I didn't find anything specific to GMT800s and this rollover valve. Almost all the trouble topics I found were resolved with replacing the three parts I already have, purge valve / solenoid, vent valve / solenoid, evaporative (charcoal) canister, or some form of broken plumbing line. And at mileages far lower than our Tahoe. Likewise fuel pump replacements. So it seems once again I've drawn the oddball problem. If I hadn't been able to figure it and do the work myself, the whole thing might have cost $1500++. As it is, it will wind up costing about $380 and some of my time.

 

[Hillbilly Heaven]

Your diagram doesn't show the vent line that runs parallel to the filler neck. Does it go direct to the tank from the filler neck just below the nozzle gate?

 

[rayra]

Yes, essentially. It parallels the main filler hose / pipe. But it is not the main vent of the tank. It's in the background of some of the earlier evap pix, alongside the rear axle vent line that also terminates up at the inner top side of the filler .

 

[Hillbilly Heaven]

That parallel hose from the tank to the filler neck is the main vent used during refueling. The rollover/vent valve mounted in tank is used during running or parked conditions. During running it prevents vacuum from building in tank by allowing air to enter tank and also tied into vapor canister and recovery system. When parked pressure can build in tank from heat. That rollover vent valve will vent that excess pressure. Not sure if that excess pressure is vented to atmosphere or thru vapor canister. Also one more safety device is built into the cap itself. That rollover vent valve has nothing to do with refueling! The hoses are too small to vent the volume of air required during fueling.

Think about this and it will make sense. Think how large that nozzle is and how much fuel is going into when nozzle is wide open. As much fuel that is flowing in the same amount of air has to leave tank so the fuel can get in the tank. I think your problem is between the filler cap and the tank not in the vapor system.

 

[rayra]

I'm mildly disagreeing, based on my study of the specific diagrams and parts for this vehicle. The rollover and tank vent to the evap canister are the same line. And on this vehicle appear to be a larger inner diameter than the fuel filler vent hose.
I've taken some more photos this morning and will post them later this evening as illustration.
I'll also note that the filler line on this later-half gmt800 ('03-'06) is much smaller than the earlier years, not much larger than than my thumb or the gas pump nozzle. The filler vent hose is no bigger than 1/4". The evap vent line is at least 3/8" ID.

And I'll point out the tests and successful pumping yesterday. Air / fuel vapors are supposed to flow out of the tank to and thru the evap and on out thru the vent valve.
That's in addition to the vent line at the filler neck.
But that filler vent is moot in a way as it dumps into the fill pipe at the neck, merging with the fill hose and contributing to the vapor load reaching the pump nozzle. It is the blockage of the evap line which causes higher vapor loads out the filler, leading to automated pump shutoff.

The blockage of the rollover would also explain the increased gurgling I mentioned earlier when tryin to fill. With the rollover / line to the evap closed off, ALL the air displaced by the incoming fuel has to go out the filler

My 02 Sub appears to have a 2-2.5" filler hose, compared to the 1" 1.25"? line of the 05 Tahoe.

I still intend to pull the filler and filler vent hoses off the Tahoe for inspection, maybe next weekend

 

[Hillbilly Heaven]

Now that all makes sense knowing the hose sizes and your explanation of the added loaded on the filler neck vent hose if the evap system is not working.

 

[fl0w3n]

I fricken miss the days of my Duramax. It was really quite spectacular, get this... so there was this tube with a cap on it, and when you took the cap off, you could pour diesel in from any angle/place/speed/direction. And when it got all the way up to the top of the neck, you could stop and put the cap back on. It was really magical.

 

[NevadaLover]

I fricken miss the days of my Duramax. It was really quite spectacular, get this... so there was this tube with a cap on it, and when you took the cap off, you could pour diesel in from any angle/place/speed/direction. And when it got all the way up to the top of the neck, you could stop and put the cap back on. It was really magical.

That's because, get this... diesel fumes aren't flammable or harmful to the environment! Thanks california!

 

[rayra]

 

[rayra]

well the next filling was today, expecting to put in ~21gal, it took 7gal and tripped. Reset and it took the other 14 before cutting off again. Still haven't pulled the filler hoses. Been distracted re-working ~6800 9mm cartridges.

It will do for now. Not excited about the idea of dropping the tank and putting in a new fuel pump. And still idly googling for more anecdotes looking for other possible causes or diagnostic methods. But expect to spend some future weekend changing the pump assambly.


eta the Delco pump

the white connector is the electrical for the pump. The black should be the pressure relief valve. The top pipe connected to the hose below should be the fuel supply. One of the other two should be the vent line - note there's no apparent rollover valve / float on either of those unconnected pipe fittings. The other might be the vent line that goes to the fuel filler. But I don't know and haven't yet found any detailed diagrams of the connections.

eta does a multi-port fuel injection system even have a fuel return line? or is the pump just commanded to pump to maintain the pressure in the fuel rail?


eta

Haynes manual in sections on removing fuel tank and replacing pump, Chapter 4, sec 7.4 "Disconnect the fuel lines and EVAP line from the fuel pump module." And the illustration photos whose 3 parallel same-sized pipes. But it's a manual for GMT800 pickups and SUVs both.

Just don't want to go thru the effort of changing the pump assembly and still have the same problem. Going to have ot make sure and pull the filler and vent hoses next weekend.

 

[ajmaudio]

6800... nice.. got any extra? lol... my brass supply is low