04 Sierra 2500HD gas tank

megabell · October 3, 2006

GMC Sierra 2500HD gas tank is very slow to take gas. It started with a "tighten fuel cap" message on my display. I then tightened it and the error message came back. I then cleaned the gasket and the intake stem and the message came back and now it went to the "check engine" light. (This seems to be a default error message for a possible loss of tank pressure.) This went on for a couple of months before I started having problems getting gas at the pump. The pump shuts off after about 1/2 gallon went in and as I tried to continue to pump the pump kept clicking off. I could hear a slow whoosh as the small amount of gas that was able to go in actually made it to the tank. I disconnected the vent hose to check for any obstructions and there were none. I took the gas tank right off and troubleshot the fuel inlet valve and all the hoses. The check valve at the tank for venting appeared to be stuck and faulty. At this point, I decided to replace the fuel tank. The new tank, unfortunately, did not fix my slow to get gas problem. This truck has the vapor recovery system which I haven't changed or serviced. So, this is where I'm at. Could it have something to do with the vapor recovery system? If anyone has experienced this or can lead me in the right direction it would be great. Thanks

GM-Tech · October 3, 2006

Usually, the vent in the top of the tank causes this problem. However, a new tank would have fixed it if that were the case. There have also been some filler neck issues, but not on your vehicle, which is a 2004 according to your profile... is that correct? This is a gas engine, right?

My next choice would be the evap vent valve. We have our fair share of problems with those, though usually they don't seal and just cause that "check gas cap" mesage and eventually set the SES light on. You could try blowing through the vent valve with the key off and see if it freely passes air.

megabell · October 6, 2006

I replaced the purge valve solenoid on the intake manifold and cleared the DTC that brought in the SES. I have been driving with it like that through a few decent cycles and the SES has stayed off. ...but, the tank is still not letting gas in freely. It constantly trips the pump off. Still not venting? Could it have something to do with the canister mounted on the back of the tank? Is that the PCM?

GM-Tech · October 6, 2006

The purge valve wouldn't have any effect on the filling problem. It's the vent valve that's important. The PCM is under the hood. The evap canister is next to the gas tank.

megabell · October 7, 2006

The purge valve wouldn't have any effect on the filling problem. It's the vent valve that's important. The PCM is under the hood. The evap canister is next to the gas tank.

<{POST_SNAPBACK}>

Could there be some problem with another component of the vapor recovery system? Will this thing keep air from displacing as I pump gas into the tank? I'm pretty confident that the vent valve and hose running up the fill tube is working properly but what would you do to test them in case I'm wrong.

GM-Tech · October 7, 2006

what would you do to test them in case I'm wrong.

<{POST_SNAPBACK}>

There are a number of tests that can be run with our scanner to see, first off all, if the valve is able to be turned on/off, then see if it's able to hold/vent vacuum.

If you want to try a manual method, turn the ign. OFF, then attempt to blow, by mouth, through the hose that connects to the valve. The valve is normally open, so it should allow air to pass through when it has no ign. power.

megabell · October 7, 2006

what would you do to test them in case I'm wrong.

<{POST_SNAPBACK}>

There are a number of tests that can be run with our scanner to see, first off all, if the valve is able to be turned on/off, then see if it's able to hold/vent vacuum.

If you want to try a manual method, turn the ign. OFF, then attempt to blow, by mouth, through the hose that connects to the valve. The valve is normally open, so it should allow air to pass through when it has no ign. power.

<{POST_SNAPBACK}>

OK, I have a stupid question. I just want to make 100% sure I'm doing it right. Where would this vent be located? It's not the one on top of the tank, molded in and hosed up to the fill inlet? Right? The SES came in again, P0446 EVAP...vent circuit malfunction. Is this the one that's slowing down the fuel going in? Thanks for your patience, this is really helping me alot.

GM-Tech · October 7, 2006

The vent solenoid is the only solenoid anywhere near the tank. It's either on the top of the tank or on the charcoal canister. It's electrical so it has an electrical connector. The check valve on the top of the tank is purely mechanical and not controlled by the PCM. The purge solenoid is on the intake, so you can't get that one wrong.

If the vent solenoid is not open, as it should be when the key is off and you're filling the tank, it can contribute to the problem you're having.