Venting a Charcoal Carbon Vapor Canister...

[DaveyGeez]

gas cap

I'm not sure what happens to a response to this thread when three years have passed since the previous, but here goes. Finding this thread has made my day after having searched online for the past couple days.

I've been upgrading my My 1956 Ford Ranchwagon for the past five years thinking each year that it's finished. During this time I've noticed the pressure build up in the gas tank every time I open the cap and wondered why. Now I can account for it with three causes: the exhaust tail pipes are within an inch of the tank; the fuel return line from the FiTech EFI adds pressure; the custom 30 gal. gas tank has no baffles; the gas cap vents in one direction only, letting air in to replace fuel consumed, but not out for positive pressure relief.

That last item got me thinking about venting to a charcoal canister and set me on the path to this forum. A big thank you to every contributor for your logic and resources provided!

Now my question. Should I change to a completely sealed gas cap or stick with the one-way venting? Is negative tank pressure possible having a charcoal canister vent system routed from the filler tube a few inches below the cap and above the fuel return line (also fed into the filler tube), to the canister then to the air cleaner? If there is also a 12V purge valve included in the system there might be some negative pressure when everything cools down at night. This might cause starting problems in the morning so I'm thinking my one way vented cap might be the way to go.

Dave

1956 Ranchwagon; 302ci.; FiTech EFI; GearVendor overdrive; rack/pinion power steering & coil over shocks; Edelbrock intake/heads; Howard RV/towing cam....too much to list it all.

 

[DirtDonk]

Hey Davey, welcome to classicbroncos. And yep, even after all this time it stays active so anyone that has posted to this thread will get a notification that you added your comments.
Glad to hear it did you some good too. Or at least led you down a potentially successful path at least!
Very cool vehicle too it sounds like. So where are the pics! As you may have gathered, we love to see shots of what anyone is working on even when it's not a Bronco (but especially Broncos of course;D ) so if you've got any that are already online, post up a link so we can check it out.
You can also use the Garage and Gallery functions in your User CP up above.

Regarding the gas cap, I'm not sure if your vehicle will accept a modern cap or not. The Broncos at least were "keyed" so that the early vented caps would not fit on the later non-vented cap equipped vehicles. Maybe yours is the same?
It's not an insurmountable issue, but maybe you won't even need it because with the venting of the canister added to the system the vapors might find that the path of least resistance and will capture it before it gets out of the old cap.
We can hope anyway...

Good luck.

Paul

 

[landshark99]

I'm not sure what happens to a response to this thread when three years have passed since the previous, but here goes. Finding this thread has made my day after having searched online for the past couple days.

I've been upgrading my My 1956 Ford Ranchwagon for the past five years thinking each year that it's finished. During this time I've noticed the pressure build up in the gas tank every time I open the cap and wondered why. Now I can account for it with three causes: the exhaust tail pipes are within an inch of the tank; the fuel return line from the FiTech EFI adds pressure; the custom 30 gal. gas tank has no baffles; the gas cap vents in one direction only, letting air in to replace fuel consumed, but not out for positive pressure relief.

That last item got me thinking about venting to a charcoal canister and set me on the path to this forum. A big thank you to every contributor for your logic and resources provided!

Now my question. Should I change to a completely sealed gas cap or stick with the one-way venting? Is negative tank pressure possible having a charcoal canister vent system routed from the filler tube a few inches below the cap and above the fuel return line (also fed into the filler tube), to the canister then to the air cleaner? If there is also a 12V purge valve included in the system there might be some negative pressure when everything cools down at night. This might cause starting problems in the morning so I'm thinking my one way vented cap might be the way to go.

Dave

1956 Ranchwagon; 302ci.; FiTech EFI; GearVendor overdrive; rack/pinion power steering & coil over shocks; Edelbrock intake/heads; Howard RV/towing cam....too much to list it all.

Stick with your one way cap - the charcoal canister should allow the tank to "breath" if the line going to the charcoal canister is large enough in diameter to account for pressure+heat differences. Obviously sitting in the shade or cooler weather the tank won't have allot of pressure changes. If the truck is sitting in the sun or running on a hot day it will need a place for the air to expand to so the cap + charcoal canister should allow this.

it is possible to have some negative pressure in the tank if the tank quickly cools down but can't suck in fresh air fast enough through the canister. To make sure this doesn't happen I wouldn't run anything smaller than a 3/8 line from the tank/filler tube to the canister, make sure you put at least one loop in the line, put the canister higher than the filler opening and I would recommend a discriminator value inline to make sure the canister doesn't suck up fuel if its possible the breather line near the tank is in a place that fuel could reach it.

 

[DaveyGeez]

I've ordered a bunch of parts from Amazon including the CC, inline roll over check valve, and 5/16" gas vent line. Then I read your suggestion of 3/8" minimum. My thinking was the excess pressure in the gas tank could only move up the 5/16" tube. There is no other option for the fumes. The tank filler cap only allows air in, not fumes out. So, even 1/4" would relieve pressure. Time will tell.

Has anyone actually cut open the CC? There are a number of options for routing two hoses. The only reason for the CC is to neutralized the volatile fumes. I'm guessing it doesn't matter which port the hose to the air cleaner attaches. It's simply drawing off excess gas fumes. Maybe the large diameter tower ports would work best since the draw from the large surface air cleaner is minimal. Putting vented mushroom caps on those large ports might defeat the carb draw. Hopefully, once the engine is off, and systems are cooling, all tank pressure is relieved. If not, it's either moving out the vent caps or out the air filter. Not much difference.

Hard to say without knowing the routing within the CC.

BTW, my Ford 302 has a FiTech #30001 EFI with their frame mounted pump and filter.

 

[landshark99]

I've ordered a bunch of parts from Amazon including the CC, inline roll over check valve, and 5/16" gas vent line. Then I read your suggestion of 3/8" minimum. My thinking was the excess pressure in the gas tank could only move up the 5/16" tube. There is no other option for the fumes. The tank filler cap only allows air in, not fumes out. So, even 1/4" would relieve pressure. Time will tell.

Has anyone actually cut open the CC? There are a number of options for routing two hoses. The only reason for the CC is to neutralized the volatile fumes. I'm guessing it doesn't matter which port the hose to the air cleaner attaches. It's simply drawing off excess gas fumes. Maybe the large diameter tower ports would work best since the draw from the large surface air cleaner is minimal. Putting vented mushroom caps on those large ports might defeat the carb draw. Hopefully, once the engine is off, and systems are cooling, all tank pressure is relieved. If not, it's either moving out the vent caps or out the air filter. Not much difference.

Hard to say without knowing the routing within the CC.

BTW, my Ford 302 has a FiTech #30001 EFI with their frame mounted pump and filter.

Yup i forgot about the cap letting in and not out - makes sense, I went to a sealed cap a while ago and let all the air purge through the Charcoal canister - i think you will be fine with that hose size, the large size is nice to have but you probably won't see a difference.

 

[DaveyGeez]

My parts will not arrive for at least a week. In the meantime, I'm searching for an internal diagram of the CC without much success so far. After reading the entire thread twice I tend to agree with EricBee as to the hose connections, that is, smallest port to the tank and a tower port to the air cleaner. I'll start with the other ports shut off, then see if venting the second tower makes a difference.

 

[73azbronco]

Wish I would have cracked open an old one, I know the smaller ports are one to the tank, I think the other to the vacuum solenoid to vacuum on an efi. No efi then largest port to air cleaner port so air is gently pulled across charcoal. Just wish I knew which smaller port is best to tank.

look at this

https://www.youtube.com/watch?v=EA3fm_UackQ

 

[DaveyGeez]

Hey 73az, that was the best instructional youtube video (https://www.youtube.com/watch?v=EA3fm_UackQ) I've ever watched! That guy never missed a beat and at the same time showed all parts cut open, their function and operation in the system. Thanks!

 

[DaveyGeez]

Sorry to beat a dead horse, but now that I have most of the parts, do you think the small port and the medium port of the canister go to the same place inside? I'd like to use the medium since it fits my 5/16" tank vent hose better and cap off the small one. Otherwise I'll put some sort of sleeve over the small one to tighten the fit.

 

[gr8scott]

do you think the small port and the medium port of the canister go to the same place inside?

Yes they do.

I'd like to use the medium since it fits my 5/16" tank vent hose better and cap off the small one.

Exactly how I did mine.

 

[DaveyGeez]

The canister is installed and worked perfectly until parking on a steep hill. The canister flooded with fuel and seeped into the air filter base. I took my chances with installation thinking the gas tank was low enough and did not include a purge valve solenoid before the canister. Duh.

I'm guessing this would have happened with the engine running as well. What solenoid/sensors do I need to detect and stop the flow of fuel as opposed to vapors up the 5/16" vent hose?

There are so many to choose from but they are all specified to fit a particular vehicle, not my custom built '56 Ford (302c.i. with Fitech #30001 EFI).

 

[DirtDonk]

Which tank do you have again? And which canister?
Where exactly did you mount it?
And where exactly did you plumb the air cleaner end?

I was wondering earlier, on that hose and fitting size you quoted. You said the medium one matched the vent line on the tank, correct? If so that would be extremely unusual in my experience. The medium one is 3/8" or thereabouts, which is the same size as the fuel feed line to the engine.
All Bronco tanks that I'm aware of use the smallest of the ports for venting. Something like 1/4" tubing.

The medium size one on the canister is the one used to vent to the engine on the modern engines with solenoids, but can also be utilized on an older engine too.
But I've never seen it used as the vent from the tank itself.

The problem with how easy liquid flows forward into the canister is not just how full the tank is, although that plays a big role, but it's all about the siphoning effect. Once flow is started, it can keep going under it's own inertial even after the vehicle is level again, and until the inlet sucks air.
If you connected to a 3/8" feed line that's pulling from the bottom of the tank, it's never going to be an appropriate vent.
I drained my entire 23 gallon NWMP tank sitting on the ground one time. Tilted it just enough to get it flowing and it did the rest. All I had to do was keep changing receiving containers each time one would fill up.

Maybe you have a custom tank where the vent line is larger than normal. Or maybe that one you're using is actually a feed or return line fitting, which would likely put it at the bottom and always submerged in gas. Not a good spot.

Anyway, I'll try to go back and see what tank we're dealing with again. Sorry if I re-hashed stuff that's all been worked out, but obviously pulling from the bottom of the tank, or attaching the engine side to vacuum is going to pull gas in quickly. Maybe double check that the tank fitting you used does not extend down deep into the tank.

Paul

 

[DirtDonk]

OOps, sorry Davey. I forgot we were working on a Ranch Wagon with custom tank.
So while much of my previous dialog does not count, the concepts are the same.

1. Mount the canister high as you can.
2. Connect the engine side vent to the air cleaner and never to vacuum.
3. Make sure that the port you use on the tank is open to the top of the tank, not the bottom.
4. And find an anti-rollover valve that will do the job.

To that last, I have not looked at the links yet, and have not spent much time sourcing one myself, but they're out there in various guises. Maybe get the one for the Delorian that everybody talks about? Or find one from a '76 or '77 Bronco? Or maybe find out what the later trucks used.

I'll see what I can come up with. In the meantime, got any pics of your tank? And some of how you mounted the canister too if you would.

Thanks!

Paul

 

[DaveyGeez]

Paul,
I followed all of your points. The vapor line starts at the tank filler neck (sealed cap), continues along the frame then up to the highest point on the firewall. I've looked at anti-rollover valves, but I doubt they would seal off liquid fuel until there's an actual rollover. They all rely on a steel ball not a float to seal the passage. Do you know of one with a float seal?

I'll see if I can dig up some photos. In the meantime, the tank is a simple stainless box fitted between the frame members, about 30 gal., with a filler neck and a parallel vent tube at a top corner that returns to the filler neck near the "sealed" cap. (The cap will let air in, but not out.)

Thanks,
Davey

 

[DaveyGeez]

A couple more details of my installation:
- 5/16" hose from sealed filler neck to high point at firewall into middle port of canister
- 1" hose from one top port of canister to air filter base fitting.
- Other top port has vented cap.
(Why didn't the fuel go out the vented cap you might ask? Hmmm...maybe it's not well vented. Or maybe the fuel saw the slight vacuum from the air cleaner and preferred that route?)

 

[DirtDonk]

Good question! Not sure what is going on in there that would not show up at the lower vented fitting first. Before finding it's way all the way over to the air cleaner.

I wonder if the fact that it's taken from the filler neck instead of the tank is literally letting fuel get lightly pumped into the vent system during filling. Even just getting some splash now and then while filling might do this I suppose.
And being a custom tank I wonder if there is even an air space when it's full. Most likely (like most) the filler neck probably ends right at the top of the tank so it's very easy to fill the tank so full it will back up into the neck slightly. Then for sure it expands into the neck when it heats up during the day.
And if it is indeed still pressurizing, well, guess where the pressure is going! Out to the canister!

For now, until you get it sorted totally, I wonder if just leaving more air at the top by not filling it as full, and then driving around with the cap loose would stop the gas being forced into the canister system.

A loose cap may let gas leak out on to your paint though, which can be bad if new paint. If you're going to change caps anyway though, perhaps just a small hole drilled into the top part to let pressure escape.

It won't do anything to help reduce fumes, but it will help with the pressurizing. Sounds like the pressure is just too much and there is too much liquid being forced into the evap plumbing as it sits now.
The only temporary solution other than the "custom" vented cap, would be a plain reservoir mounted up higher than the canister. But given where your canister is now, I'm not sure that it would be feasible for most vehicles.
But it would still catch some of the gas and return it to the tank before it got to the canister's charcoal media, so there is that.

Good luck.

Paul

 

[DaveyGeez]

Thanks for your thoughts Paul.

I should note, all of this happened with a tank half empty, or half full as you might say. As for fill gas traveling up the vapor tube, that's a good point. Maybe there was gas in the line all along and didn't fill the canister on the firewall until the car was pointed downhill.

That brings me back to some sort of float check valve in the vapor line. Also a loop in the 5/16" vapor line (in an upward direction) near the fill tube might help. I think someone else suggested that earlier in this thread.

I've been hunting for "float check valve" online without any luck so far.

 

[DaveyGeez]

Here's the tank and the filler neck photos:

URL? Really? I can't drag/drop from my files?
Guess I need help with that too

 

[McLeod]

I installed the rollover valve from Coyote in the top of the tank. My tank has two small bungs at the very top of the sidewall where the filler neck goes into tank.It should stop liquid either right side up or upside down, but vapor should flow through it without a problem.

What I did, and I think this is the key, is to mount the vapor line so there were no low spots to collect liquid. A gradual climb to the charcoal canister mounted high in engine compartment.
If you create a loop vent where the vent goes really high near the tank you might have a problem with the vapor liquefying on the other side of the high loop with no way to drain back to tank.

 

[DaveyGeez]

Does that Coyote rollover valve operate with a steel ball or a float mechanism?
I'm thinking of adapting it to an in-line (vertical) situation close to the tank, rather than remove and drill my tank.
My current venting is a 5/16" hose teed into vent tube about 6" above the tank. Below that tee is another where the EFI return line is piped. The vent tube rises from the tank parallel to the tank fill tube. It then enters the fill tube just below the semi-sealed cap. I say semi because it will let air in but not vapors out. (If I could only figure out how to attach photos...)

As for a slight uphill vent line run all the way from behind the rear axle to the canister under the hood, what happens when you park pointing down hill?