Calling Charcoal Canister Experts!!!! PS: I've searched!

[NorCalFJ100]

I was recently on a 10 day road trip. Travelled far and wide. Started at sea level and hit 11k elevation several times. It was also very hot. At home and around town I would occasionally get a little extra built up pressure that was evident when opening the gas cap. That would last maybe 5-10 seconds...

On my trip once I started gaining elevation and built up heat I am assuming, my CC problems got much worse. At one point it would hiss for 10+ minutes...opening the gas cap very slowly.

The only replacement CC I could find quickly was on Amazon: ACDelco 215-153 and was able to have it delivered ahead of one of my legs. Problem solved. I thought.

Hooked up both the tank and purge lines and since the 3rd line came from the bottom of the OEM canister, I just left that off for now. Gas cap issues were solved. However, I could smell gas quite a bit coming from the engine bay. Stopped at an auto parts store and bought a short piece of gas line and hooked up the 3rd hose. Gas smell is gone!

Next fill up however the pressure was back and needed about 10 minutes to relieve itself. Immediately pulled that 3rd hose off and remaining fill ups were fine.

I finally made it home and inspected it further thinking there was some blockage in the breather hose somewhere, but when blowing into that hose it seems to be all clear. No resistance.

What on earth could the issue be? Anyone experience this before?

 

[TriaxialBulls]

So that "third hose" coming out of the bottom of the canister is just an overflow hose that vents to atmosphere when the canister gets more fumes than it can handle. So the reason you were smelling gas without it is that these overflow fumes weren't being routed downward and out of the engine bay in that scenario.

To me, it sounds like it's an issue with purging the canister; I'd guess that there's a fault with some of the vacuum equipment underneath the manifold. I'm not really an expert on how that part of the system works so I can't say what would be faulty.

 

[NorCalFJ100]

So that "third hose" coming out of the bottom of the canister is just an overflow hose that vents to atmosphere when the canister gets more fumes than it can handle. So the reason you were smelling gas without it is that these overflow fumes weren't being routed downward and out of the engine bay in that scenario.

To me, it sounds like it's an issue with purging the canister; I'd guess that there's a fault with some of the vacuum equipment underneath the manifold. I'm not really an expert on how that part of the system works so I can't say what would be faulty.

Yes, that is what I understand as well. That third hose just routes down to where the diff breather is. It's just very strange that when it is hooked up the pressure builds, but without it the pressure is fine.

This is a brand new canister. But it is doing the same thing as the OEM. But again when I blow through that hose there is no resistance. Doesn't make sense. I thought for sure I would find a clog or something causing it to not ventilate properly.

 

[Jgrauman]

Yes, that is what I understand as well. That third hose just routes down to where the diff breather is. It's just very strange that when it is hooked up the pressure builds, but without it the pressure is fine.

This is a brand new canister. But it is doing the same thing as the OEM. But again when I blow through that hose there is no resistance. Doesn't make sense. I thought for sure I would find a clog or something causing it to not ventilate properly.

I put an end to my Charcoal Canister problems for good!

In the past I rebuilt my canister but recently the problem popped back up and once I experience a problem 3 times I change directions and look for a final fix. The canister has 3 lines - 1 - comes straight from the tank with a one way valve at the canister < the problem 1 - goes to the VCV...

forum.ih8mud.com

 

[NorCalFJ100]

I put an end to my Charcoal Canister problems for good!

In the past I rebuilt my canister but recently the problem popped back up and once I experience a problem 3 times I change directions and look for a final fix. The canister has 3 lines - 1 - comes straight from the tank with a one way valve at the canister < the problem 1 - goes to the VCV...

forum.ih8mud.com

Yes, I saw that thread but I would rather not remove that ball check valve if I can help it. One thing that was mentioned is that by not having that it could cause moisture to build in the tank over time and cause rust.

 

[TriaxialBulls]

Yes, I saw that thread but I would rather not remove that ball check valve if I can help it. One thing that was mentioned is that by not having that it could cause moisture to build in the tank over time and cause rust.

You could also just replace the whole canister with a small inline fuel filter that vents to atmosphere. This would take care of all your problems, eliminate a bunch of unnecessary crap in your engine bay, and is really cheap.

 

[BILT4ME]

Does your new canister cross-reference to the VC-120? That's what most of us have gone to.

 

[NorCalFJ100]

Does your new canister cross-reference to the VC-120? That's what most of us have gone to.

I could not find the VC 120 while on the road unfortunately. I did find several threads on Mud where people used this ACDelco unit.

 

[NorCalFJ100]

You could also just replace the whole canister with a small inline fuel filter that vents to atmosphere. This would take care of all your problems, eliminate a bunch of unnecessary crap in your engine bay, and is really cheap.

I would consider this, but just spent $75 ordering this unit. Prefer to keep as much of the OE equipment intact...I also live in the depths of smog check country.

 

[Rifleman]

Please don't forget that during the summer months many states are required by the EPA to use an ethanol blended gasoline. With Ethanol added to gasoline, plus the summer heat it seems to produce way more vapor then just regular gasoline does.

 

[NorCalFJ100]

Please don't forget that during the summer months many states are required by the EPA to use an ethanol blended gasoline. With Ethanol added to gasoline, plus the summer heat it seems to produce way more vapor then just regular gasoline does.

I can understand that, but hissing for several minutes to probably 10 minutes makes me think something is not right. Now I was leaving Colorado and driving into Arizona when I noticed the hissing making a come back. I am not exactly sure of the ambient tems on the freeway, but guessing well over 100 outside.

 

[TriaxialBulls]

I would consider this, but just spent $75 ordering this unit. Prefer to keep as much of the OE equipment intact...I also live in the depths of smog check country.

You said you got it off Amazon. Couldn’t you just return it? And I thought they didn’t do a visual inspection for OBD2 vehicles?

 

[NorCalFJ100]

You said you got it off Amazon. Couldn’t you just return it? And I thought they didn’t do a visual inspection for OBD2 vehicles?

They look at absolutely everything here in California...it's awful. I guess I could return it, but again trying to keep all the OE operating equipment intact.

 

[Woofythewolf]

A basic system overview for engine off operation is that fumes flow from gas tank -> to tank port on EVAP canister -> drain port on evap canister. It should be filtered at that point and not smell like gas. the drain port should be free and clear, not blocked by a chunk of mud or something.

When you turn on the engine (and it exceeds a certain temperature) the computer opens a solenoid valve that connects the engine to the purge pipe, pulling a vacuum on the canister. This pulls air from the tank (until the tank is at the same vacuum as the engine and then no more air flows from it) so then all the air flows in through the drain pipe, through the carbon (to remove captured gas fumes from the carbon) and then out the purge pipe into the engine to be burned.

So you need to check that when you blow into the tank port, you get air from both the purge and drain (maybe test one at a time by blocking each), and that when you blow into the drain port you get air from the purge. If that checks out, then you need to check the drain line for blockage, and the tank line for blockage.

Even if the electronic valve doesn't work you shouldn't have pressure in the system, but eventually the carbon will saturate and you'll get gas fumes from the drain line. So if everything checks out like above then it's a vacuum line (hopefully) or your VSV under the intake which is a pain to do. It's really tight under there.

And I know how it is in California, I even went so far as to drill a (smaller than stock) EGR passage in my foreign market non-EGR head to keep the EGR system working properly. I get better than perfect emissions even at 380,000-ish miles though!

 

[NorCalFJ100]

A basic system overview for engine off operation is that fumes flow from gas tank -> to tank port on EVAP canister -> drain port on evap canister. It should be filtered at that point and not smell like gas. the drain port should be free and clear, not blocked by a chunk of mud or something.

When you turn on the engine (and it exceeds a certain temperature) the computer opens a solenoid valve that connects the engine to the purge pipe, pulling a vacuum on the canister. This pulls air from the tank (until the tank is at the same vacuum as the engine and then no more air flows from it) so then all the air flows in through the drain pipe, through the carbon (to remove captured gas fumes from the carbon) and then out the purge pipe into the engine to be burned.

So you need to check that when you blow into the tank port, you get air from both the purge and drain (maybe test one at a time by blocking each), and that when you blow into the drain port you get air from the purge. If that checks out, then you need to check the drain line for blockage, and the tank line for blockage.

Even if the electronic valve doesn't work you shouldn't have pressure in the system, but eventually the carbon will saturate and you'll get gas fumes from the drain line. So if everything checks out like above then it's a vacuum line (hopefully) or your VSV under the intake which is a pain to do. It's really tight under there.

And I know how it is in California, I even went so far as to drill a (smaller than stock) EGR passage in my foreign market non-EGR head to keep the EGR system working properly. I get better than perfect emissions even at 380,000-ish miles though!
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Thank you! I will give this a try. I saved my original CC and perhaps I can fix it...I will try the solution that @LandCruiserPhil laid out as well.

I am still confused as to why I would have so much pressure in the tank with the drain pipe hose hooked up and no pressure in the tank when I remove the drain hose. I must be missing something.

 

[Woofythewolf]

Does the pressure release when you disconnect the drain hose? sounds like maybe it got blocked by mud or something. Or if it has one of the diff breather type float blockers maybe that is stuck closed.

 

[NorCalFJ100]

Does the pressure release when you disconnect the drain hose? sounds like maybe it got blocked by mud or something. Or if it has one of the diff breather type float blockers maybe that is stuck closed.

Well what I know is that when I replaced the CC during my trip, I did not have the extension hose to connect to the drain pipe....got a few tanks of gas and everything was great, but could smell gas in the engine bay. I made my way to an auto parts store to get some hose, connected and gas smell was gone.

Next tank of gas the pressure was back. I did not try to pull the hose at that point. I let it vent via the filler and then removed the hose.

When I got home I blew through the hose and it was perfectly clear and no resistance. I thought for sure it was blocked/clogged.

 

[LandCruiserPhil]

Does the pressure release when you disconnect the drain hose? sounds like maybe it got blocked by mud or something. Or if it has one of the diff breather type float blockers maybe that is stuck closed.

What are you calling the drain hose? There should zero pressure where the line comes into the canister. There is nothing including no check valve between the tank and canister.

Note - By removing the ball in the canister as many have done here in Arizona you will not get any bad effects including zero moisture.

 

[Rifleman]

Does the pressure release when you disconnect the drain hose? sounds like maybe it got blocked by mud or something. Or if it has one of the diff breather type float blockers maybe that is stuck closed.

Don't discount the idea of the drain/vent hose being plugged up. When i rebuilt my factory C.C. i found a whole family of dead earwigs plugging up my bottom C.C. drain/vent hose.

 

[Woofythewolf]

What are you calling the drain hose?

The port the FSM page calls the drain. I try to make things less confusing when I can.


TLR, as long as you have a functional VSV OR a VSV failed closed, the check valves actually do nothing.

In thinking about how the system works, with the electronically controlled VSV it shouldn't need any check valves. With VSV closed gas vapors escape the tank through the carbon, and with the VSV open when the engine runs the carbon gets refreshed. Therefore, I'm thinking they're not there as check valves but rather flow restrictors that require a minimum pressure to push the ball off its seat and allow gas to pass through in the event of a VSV failure. Specifically, the non-existent VSV open failure. (at least i've never seen someone have that issue that here on the forums). That "minimum pressure" would be easily exceeded by engine vacuum so it acts as if it isn't there when the engine is running.

That way, if the VSV fails in the open position (even though they always seem to fail closed), the gases will be forced to push out through the carbon rather than escape through the otherwise unrestricted intake passage, due to the minimum pressure required to push open the valve, and the carbon is then an easier escape.

Again in the VSV failing open situation, if the gas tank tank is sucking in air due to contraction, it is forced to pull it in through the carbon rather than just coming from the air intake (this time it is actually acting as a check valve), and refresh the carbon while it does so. ( this would be for long term storage, with the VSV open the carbon would be getting refreshed the whole time the engine is running. So only matters in a junked car or a car that is sitting for long periods without getting run)

I could totally see the EPA mandating that as a required failure mode of the emissions system. too bad the check valves aren't that reliable.

Side note: you could very simply make a passive EVAP system based on a single check valve with a minimum opening pressure of .5 PSI or so. Only problem is that it would be a vacuum leak that has a variable amount of fuel vapors coming from it (same as existing one) but it starts passing through before the engine is warmed up, unlike the electronically controlled one. But getting rid of a VSV and simplifying the system is pretty cool.