Slow Fuel Tank Fill

FuzzyDriver · April 14, 2008

I have a 2004 4x4 GMC Sierra short-bed with the most annoying problem. My truck has 54000 miles and only got this particular problem a month or so ago.

Problem: I can only put about .3 gallons in the tank before the automatic nozzle trips off. If I restart immediately then it trips immediately. If I wait a while I can put in another .3 gallons or so before it trips.

It takes FOREVER to fill the tank this way. I noticed that if I listen I can hear the sound of air coming from the filler pipe. When the tank is VERY low (almost empty) I can put in about 1.2 gallons before the first trip; after that it's .3. Logically, this tells me that (1) the filler must extend into the tank to nearly the bottom, allowing it to vent until the level reaches that point and (2) my filler pipe holds about .3 gallons. It also tells me that the vent is not venting, or is venting VERY slowly.

I disconnected the vent tube at the top of the filler pipe. Inside was a small brass flow constrictor. I removed it. This helped reduced the time I have to wait between .3 gallon fills, but not much.

While I was mucking about under my truck, I tried to draw a vacuum on the vent tube with a small vacuum tester. I could not draw a detectable vacuum at that slow hand-pump rate.

Next I tried my air compressor. Air flowed readily into the (nearly empty, ~ 2 gallons left) tank and began pressurizing the tank. It seems I could even hear the tank expanding. When I took the air compressor off, the air came back out kind of at the rate you can blow through a soda straw. No gas or air came out of the open vent tube at the top of the filler (I had not blocked it, which seems stupid now in retrospect as I was looking right at it). Shouldn't I have gotten a face full of gas?

Then I tried blowing air into the vent fitting. Air came right out of the vent, the tank did not pressurize.

What's going on? I need to put gas in this puppy once in a while!

I had P0442 and P0446 for about a year before this happened. Reset them a couple weeks ago during my troubleshooting efforts and no codes of any kind have reappeared (although from what I understand I haven't met the conditions for those two tests to be run, anyway).

Also, my Haynes manual says there is a sticker showing the EVAP system on the radiator support, but it isn't there. There's a flat spot when another sticker could have gone.

minibike132 · April 17, 2008

I disconnected the vent tube at the top of the filler pipe. Inside was a small brass flow constrictor. I removed it. This helped reduced the time I have to wait between .3 gallon fills, but not much.

First off I'll have to look around because I know I will not find it in a manual, pretty sure it's burried in training I just can't remember which course, but can you identify what you removed because it sounds like the spark arrestor. Just by the name you can see that isn't really something you want to leave off. Is this an E-85 compatible vehicle I think that was where I saw it?

Anyway search this site for the p0446 or for evap vent valve relocation. I'm not really sure which line you were drawing a vacuum on or blowing into but it sure sounds like a typical vent plugged issue and there is an updated kit that relocates the vent to the top of the trans area.

minibike132 · April 17, 2008

Try looking at the second post in this thread

FuzzyDriver · April 18, 2008

I disconnected the vent tube at the top of the filler pipe. Inside was a small brass flow constrictor. I removed it. This helped reduced the time I have to wait between .3 gallon fills, but not much.

First off I'll have to look around because I know I will not find it in a manual, pretty sure it's burried in training I just can't remember which course, but can you identify what you removed because it sounds like the spark arrestor. Just by the name you can see that isn't really something you want to leave off. Is this an E-85 compatible vehicle I think that was where I saw it?

Anyway search this site for the p0446 or for evap vent valve relocation. I'm not really sure which line you were drawing a vacuum on or blowing into but it sure sounds like a typical vent plugged issue and there is an updated kit that relocates the vent to the top of the trans area.

When you crawl under the truck and look up at the filler hose there are two hoses, besides the larger filler hose itself. One is the differential vent (not relevant to this discussion). The other goes to a nipple sticking out of the filler very close to the top, just below where the cap is on the other side. This is the tank vent, right? When I took the hose off the nipple, the brass constrictor was just inside the hose. I can't imagine how it would arrest a spark(??).

My truck is not an E85; it is a straight gas 5.3L V8.

Are you saying that this hose I'm describing goes to the charcoal canister rather than to the top of the fuel tank? When filling the tank, is the tank vented through the charcoal canister? I sure wish I had a diagram of my trucks EVAP system, it would make troubleshooting this problem a lot easier!

Tucson_02Silverado · April 18, 2008

Just mentioning this, as it was more common of a symptom with 70's/80's vehicles.

If you are in a constant habit of topping off the tank (making an even $ amount or gallon reading) after the nozzle clicks off the first time, over time the vapor canister eventually becomes over saturated from liquid gasoline "gumming" up the charcoal, causing a hard to fill situation.

On OBDII vehicles now, there are more sensors and solenoids for the vapor capture systems. Usually the ECM would flag an error long before you have a hard fill. But, computers, what can ya do these days.

minibike132 · April 18, 2008

is the tank vented through the charcoal canister?

yep

The evaporative emission (EVAP) control system limits fuel vapors from escaping into the atmosphere. Fuel tank vapors are allowed to move from the fuel tank, due to pressure in the tank, through the vapor pipe, into the EVAP canister. Carbon in the canister absorbs and stores the fuel vapors. Excess pressure is vented through the vent line and EVAP vent solenoid valve to the atmosphere. The EVAP canister stores the fuel vapors until the engine is able to use them. At an appropriate time, the control module will command the EVAP purge solenoid valve ON, allowing engine vacuum to be applied to the EVAP canister. With the EVAP vent solenoid valve OFF, fresh air is drawn through the vent solenoid valve and the vent line to the EVAP canister. Fresh air is drawn through the canister, pulling fuel vapors from the carbon. The air/fuel vapor mixture continues through the EVAP purge pipe and EVAP purge solenoid valve into the intake manifold to be consumed during normal combustion. The control module uses several tests to determine if the EVAP system is leaking.

So looking at the picture #4 is your tank vent it is routed to the canister #2. During fuel fill and when the tank is hot, vapor takes this path. When there is excess vapor it is pushed through tube #7 to valve #6 and vented to the atmosphere. A restriction in any of these parts can cause a refueling issue. The valve is normally open so an electrical issue is not likely. The valve is usually the issue.

As far as that screen I don't know what it is. The arrestor I was talking about is for E85 vehicles only.

(1)EVAP Canister Purge Solenoid Valve

(2)EVAP Canister

(3)Fuel Fill Neck/Fill Cap

(4)Rollover Valve/Fuel Tank Pressure (FTP) Sensor

(5)Fuel Tank

(6)EVAP Canister Vent Solenoid Valve

(7)Vent Hose/Pipe

(8)EVAP Vapor Pipe

(9)EVAP Purge Pipe

(10)EVAP Service Port

FuzzyDriver · April 19, 2008

First off, allow me to thank you for your help. I really appreciate it.

When you said you don't know what the 'screen' is for, were you refering to the brass constrictor? It is a single piece about 3/8" diameter x 5/8" long with a slight taper in both directions (I guess so you can push it into a hose easily) and about a 1/8" hole in the middle. There is no screen element.

I appreciate the drawing, too. Is this a generic EVAP system drawing? I seem to have more parts than shown here. For instance, there's no fuel tank pressure sensor shown. There's also no connection shown at the top of the fuel filler, like mine has. And the fuel filler is shown dumping out into the top of the fuel tank.

Could you verify that, inside the tank, the fuel filler runs down to near the bottom?

I can see that either the CO2 canister being clogged or the vent solenoid valve being clogged could keep the tank from venting during fill. But what does the small connection at the top of the fuel filler go to? Using your explanation, this connection can't be the vent because the vent solenoid can't go to it. The vent solenoid has to be able to vent to atmosphere during vehicle operation (which makes perfect sense per your explanation) and during that time the small connection is cut off from the atmosphere because the fuel cap doesn't vent. The small connection can only vent when the cap is off.

For troubleshooting purposes, I am going to remove the connection between the fuel tank and the CO2 canister, drive down to the gas station, and see if I can put gas in. If I can, I'll try the same thing with that line reattached, but with the vent solenoid valve connection to the CO2 cannister removed. That should tell me whether the vent restriction is in the CO2 canister or in the vent solenoid valve.

Thanks again, and I'll let you know what I find out.

FuzzyDriver · April 19, 2008

...and immediately after I posted that reply I realized the canister has nothing to do with CO2. It is Activated Charcoal, not Carbon Dioxide. My duh...

minibike132 · April 19, 2008

For most of your questions I'll be completely honest and say I don't know. I don't take particular note of any of these things unless they jump out at me or trying to find a problem leads me down that path. The restrictor, don't know never saw one. The filler going down to the bottom of the tank don't know never really paid attention, however knowing how it vents I'll hazzard a guess and say it does not extend into the tank. Yes that is a generic drawing but accurate none the less. Honestly I would have to see what your talking about on the extra hose on the neck and my truck is a diesel so I can't just go out and look at one but if I think about it Monday I will. Your trouble shooting is the way to go without involving a bunch of equipment. Good luck let me know what you find out.

minibike132 · April 19, 2008

Which engine is this? What is the L code on the option?

ZZ327 · April 19, 2008

have you tried holding the nozzle out a little so it doesnt sit all the way in the tank opening?

minibike132 · April 19, 2008

If it's an L59 you can throw everything I said out the window and call me an idiot, Ill be over here in the corner sucking my thumb. Just do me a small favor and disconnect that canister line and tell me what happens.

pennzoil29 · April 19, 2008

have you tried holding the nozzle out a little so it doesnt sit all the way in the tank opening?

"DITTO"

FuzzyDriver · April 20, 2008

If it's an L59 you can throw everything I said out the window and call me an idiot, Ill be over here in the corner sucking my thumb. Just do me a small favor and disconnect that canister line and tell me what happens.

Sparkstech, I think you can rest easy. My truck is not a flex fuel, just a regular gas-only 5.3 V8.

To the pull-the-nozzle-out guys: The tank isn't vented through the fuel filler, so no amount of making sure air can get into the fuel filler will help if the fuel enters the tank volume below the level of the fuel in the tank. {Ahem} For the record, it was the first thing I tried .

I have figured out what the trouble is. Sparkstech gave me the real clue when he said the tank was only vented out through the canister and vent solenoid valve (and not through the little line at the top of the fuel filler).

The problem is the vent solenoid valve. I disconnected the connection between the vent solenoid valve connection and the canister. I was able to fill the truck normally . This tells me the vent solenoid valve is stuck shut.

So, Sparkstech (or whoever wants to jump in). What's the chances I can fix a vent solenoid valve? Or is that doomed, and I should just go buy a new one?

The only loose end to tie up is: Just what in tarnation is that little hose at the top of the fuel filler for?!?

minibike132 · April 20, 2008

What's the chances I can fix a vent solenoid valve?

Slim to none but there is an updated part and a kit to move it to an area that isn't as likely to get plugged up. I sent you to a thread with the bulliten on my 3rd post go check out that thread.

The only loose end to tie up is: Just what in tarnation is that little hose at the top of the fuel filler for?!?

Again I'm feeling a little stupid because I just don't know I never really paid attention and It has never caused me any troubles. Good luck to you on the fix.