fuel pump pushing gas out of the vent tube

[mgb0302]

I have the Sherman tank wit in-tank pump from WH. I have it vented to open air (line run from tank to engine compartment with a few loops).

I noticed yesterday after I filled up that there was gas bubbling out of the vent hose.

I used to have the vent running directly into my air cleaner prior to my EFI MAP (atomic refi set up) but someone here recommended the additional fumes from the vent tube may throw off the computer. Either way, I can't have additional fuel just dumping into the air cleaner from the vent tube.

SO my questions are:
1) Why is the pump pushing fuel out of the vent tube.
2) Even if I were to put in a charcoal canister, I would wind up with fuel in a canister correct?

Any thoughts?

 

[DirtDonk]

I don't think the fuel pump is pushing it out. It's pressure buildup and a full tank.
If your tank is mid-'70 or newer, it's using a non-vented cap. So your vent tube is the only way out. As the fuel warms up too, as things warm up during the daytime, it just goes farther up that one small tube.
That's my theory anyway, and I'm sticking to it.

Yes, if you simply put it on a canister you will just get more gas in the canister where it does not belong.
You could use a simple catch tank and then vent that to the air filter so it eventually dries out inside.

You could use a larger diameter tube adapted to the small vent hose just to act as a larger volume so it does not make it all the way up to the other end.

You could double up the vent line. "Y" it out to a second small hose, run to the same spot even.

Re-route it back to the filter or directly to the Atomic unit somehow (depends on your filter setup I suppose) and let the computer deal with it.
In theory at least, because this is not a MAF setup, the oxygen sensor should tell the computer to reduce injector time, which should keep things running pretty consistently I would think. But I also don't think this is the best solution either.
Those that recommended re-routing it away from the filter are not wrong necessarily. I just think that the computer can handle it up to a point.
My concern would be more about the fuel dribbling into the area uncontrolled while the engine is sitting.
Seems like a fume monster waiting to be born. In a perfect storm sort of way, with you filling the tank on a cool morning and then sitting outside on a super hot summer day, you may get more liquid up the pipe than is safe.

Of course, you could fill it up a little less, but where's the fun in that!
My first choice would be a larger diameter tube run up to a high-mount charcoal canister, then plumbed to the air filter.

As a second choice, I would run the factory system the way it was from '70 to '76, with one change.
Continue using the condensing/catch tank behind the driver's shoulder, then to a high-mount charcoal canister on the firewall.

There are probably a couple of other simple solutions I'm not thinking of. Maybe some others have idears and can clear the air.%)

Paul

 

[DirtDonk]

Sorry, just saw the "few loops" comment in your description. Sounds like you were already on top of the whole volume thing.

And wondering how a pump might create the issue, maybe there is a little too much resistance (is there a possible kink somewhere?) maybe the return line is pressurizing the tank?
Or perhaps there is a leak in the outlet between the pump and tank fitting, that's also pressurizing the tank.
Never seen either, but that does not mean it can't happen.

Try leaving the cap off and see what happens.
If it still pushes fuel out of either the vent hose or the filler neck, it's not the pump. It's just fuel expansion and not enough space.
With the cap locked up and not leaking, the only place the fuel can go is up the vent line.

Do you ever get any seepage out of the gas cap?
If you had new paint you could almost guarantee that!

Paul

 

[DirtDonk]

Just thought of something else.
If fuel is collecting in the loops, then the liquid stays up away from the tank instead of draining back in during cooling or idling.
Then, any expanding pressure buildup only has to push the gas a short way to get it to spit out the top. And since any liquid in the loops is literally blocking the air passage, the pressure builds up behind it and pushes it out.
Yes, it could just bubble past it, but under the right circumstances it could push liquid with it too.
Just some more random thoughts.

Maybe a quick re-route of the vent line to make it straighter, but longer, up forward into say the front wheelwell in front of the coil might make a difference.
More work for you of course, but might help to prove or disprove that last theory.

Paul

 

[ransil]

remove the loops
I run mine high up past the filler neck then on to the charcoal canister, figure the hight will give the vapors time to condensate and run back into the tank.

 

[mgb0302]

Paul and rancid- thanks for the feedback. I am going to try stepping up the size of the vent line first. Seems to be the simplest fix.

 

[DirtDonk]

Maybe, but if the loops stay intact, and they still fill up with liquid at the bottom of each one, then you're still in close to the same dilemma with no actual venting.
But at this point it's hard to say really. Larger tubing might be enough...

Worth a try if it's easier at this point.

Good luck!

Paul