Gas Pump Shuts Off when Filling - Venting Issue

I have a 2011 Tacoma TRD OR Access Cab with the 4.0 and 5-spd Auto.

I am having trouble when filling the gas tank - With all the evaporative emissions lines connected, the fuel backs up in the filler neck, shutting off the gas pump. The air being introduced into the gas tank while pumping gas apparently has nowhere to go.

I got under the truck and disconnected the hard plastic/nylon line that goes from the top of the gas tank to the charcoal canister inlet (effectively opening the gas tank to atmosphere), then drove the short distance to the gas station. I was able to fill the tank without the gas pump stopping once, and I could hear air being pushed out of the tank (via the hard plastic/nylon line that goes to the charcoal canister).

Naturally, I suspected a blockage somewhere downstream. I removed the charcoal canister assembly from the truck. When I blow air (with my mouth) into the charcoal canister inlet, air comes out primarily from the fitting that leads to the manifold (purge valve). If I put my thumb over the fitting that leads to the manifold, and blow into the canister inlet, air comes out from where the detection pump mounts. I re-attached the detection pump to the canister and blew into the canister inlet - As before, air came out through the fitting that leads to the manifold, and from the fitting on the detection pump that leads to the "post-filter" - From these tests, I am assuming that there is no restriction to the flow of fuel vapor in either the charcoal canister or the detection pump.

I tried to blow air (with my mouth) into the hose that runs up to the manifold (purge valve), and encountered significant resistance. I unhooked this hose at the purge valve, and was able to then blow through the line. Further research indicates that the "default" position for the purge valve is "closed", so it makes sense that I was not able to blow through this line when it was hooked up to the purge valve.

I then tried to blow air (with my mouth) into the hose that runs from the charcoal canister to the "post-filter" - I was able to blow air through that line, into the "post-filter", and could hear it escaping through the vent holes at the filler neck.

I'm stumped - Something is stopping air from escaping the tank while I try to fill up, but there aren't any apparent restrictions in the charcoal canister, detection pump, post-filter, or any of the lines.

This is all with the engine off and key off.

Are there any other valves that could be stuck closed and are restricting the escape of air from the fuel tank when I try to fill up? I tried applying suction (with my mouth) to the fitting on the diaphragm at the charcoal canister inlet - I could feel the diaphragm close (and hold closed) when I applied suction, so I don't think I have a ruptured diaphragm. (I also understand that the default position of this diaphram is "open" to allow fuel vapor from the tank into the canister).

Is there a valve within the detection pump module that prevents fuel vapor from moving from the charcoal canister to the "post-filter"? (ie during the self-testing?) If so, is its default position "open"? - The fact that air will move through the detection pump leads me to believe that there is no restriction there, either.

Ideas?

 

Bumping old thread to see if you ever solved your issue? I'm having the same problem.

 

Charcoal canister will need to be replaced. I have seen spiders make nests inside the hoses blocking the lines but its rare, you can try to use and air compressor and blow it threw the filler neck vent line and lines on the canister and give it a shot but most of the time it just need to be replaced.

 

Just went thru this
1- there is a vent on the filler neck and the holes were plugged with dirt.
2 - the outlet of the vapor canister (before purge valve) was full of dirt as well.
So Desert dust + Oregon wet makes mud. Pulled the canister out and hit all the openings with an air hose - all sorts of crap blew out of the fabric filter. Reassembled and no more venting issues

 

How hard was it to get the vapor canister out?

And how did you clean the vent lines out?

 

Hardest part was the discconnects. Rest is just a plug and some fasteners.
Pulled off the purge valve and cleaned the canister outlet filter by digging out the mud and back blowing with shop air. Wound up pulling the entire filler neck out, used a pick and shop air to clean out the vent holes by the cap.

 

So you didn't have to drop the tank to get to it? I've read somewhere people saying you had to

 

Had my tank out anyway to do the fuel pump- but also pulled it back out juggle the hoses.

 

Good thread, I’m having the same problem with my 1st gen Tundra. I’m going to try your methods to clean out the vent.

 

Hello, new to the forum, I’m having the same problem with my 2002 Tacoma, I’m not technically/mechanically inclined but I follow instructions very well, can someone post a step by step process of how to get to the canister?
Thanks in advance for your help.

 

SUBD