OT: Grand Cherokee Fuel Tank Not Venting

2006 3.7l V6 Parts getter and tractor show transportation. 216k miles

Starts and runs fine otherwise. No "check engine" light

Takes gas from the pump very slowly. Hafta trickle it in or it backs up the filler neck.

Pretty good vacuum when I open the filler cap.

There is an anti-siphon device in the filler neck, I removed that to rule out a blockage.

There is a "rollover valve" in the fuel tank vent to prevent leaking if the car is upside in the ditch. Sometimes we run some pretty rough terrain and maybe it jarred into block mode. Do you think that might be it?

Is the evaporative canister "full"? Does that happen and can it be drained or deleted or do I put in a new one for $125?

I'd love to hear some advice because it's cold here and taking 10-15 minutes to gas up isn't fun. Thank you!

I had the same problem with a 2001 Ford Explorer. Changing the roll over valve didn't help. Never did find the cause but had ruled out everything except the carbon canister vent being plugged by the time I traded it off.

"Is the evaporative canister "full"? Does that happen and can it be drained or deleted or do I put in a new one for $125?"

They don't/shouldn't get full of gasoline, as you are thinking, that could be drained.

Gasoline vapor from filling the tank or the vehicle sitting an a HOT day gets captured in the charcoal in the emissions canister.

When you are driving the vehicle and it's warmed up and other conditions are met the 'puter opens a valve and allows engine manifold vacuum to draw filtered air through the charcoal, drawing off the gasoline vapors and burning them in the engine to make power.

Either in the charcoal canister or ahead of it is a simple foam or gauze filter that captures road dirt to keep it out of the engine.

Eventually, this filter clogs, causing the issue you are having.

I'm NOT familiar with the emissions system on your exact vehicle, but likely that's your issue.

Find the evil device we've been talking about and have a close look at it... sometimes the "filter" can be removed and blown clean with compressed air, and put back in place, solving the problem for YEARS and quite a few miles, otherwise you've got to replace the unit.

Also, sometimes the electrically-operated canister vent valves fail, NOT sure if yours is part of the commonly-replaced canister unit or separate.

cannister is plugged. check rockauto for a new one.

First thing. Fuel tanks are part of a closed system. As in n o vents to atmosphere. After all, in this day and time of EPA, emission controls, et al, it is a mortal sin to vent gasoline fumes to the atmosphere. Therefore no conventional vent as in the past.
Now, having said that, there are two places to look. As others have mentioned, the charcoal canister is the first place to look. You should be able to blow through it easily. Also look at the hoses to and from the canister. They can become blocked internally. Prolonged exposure to petroleum fumes along with ethanol fumes can cause them to deteriorate internally and become gummy. This is not always readily apparent from the outside of the hose. Make sure that you can blow through them.
Last but not least. Look at your filler neck. You will see that there are TWO tubes. One large, one smaller. The smaller one serves as a vent for filling the tank. Notice that it connects to the larger tube near the top. This allows the displaced air to exit above the fuel nozzle during refueling. If this smaller hose becomes kinked or collapses internally, it will interfere with refueling. If it feels soft, replace it.

I have heard that if you overfill the tank that it can flood the canister, then it won't vent properly.

Try going to jeepforum.com or nagca.org. You'll have to create an acocunt, it's free. Then post your question. They usually have pretty good answers. They have helped me on more than one occasion.

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