Has anyone had a problem with fuel leaking out of the charcoal canister after filling the gas tank full? Maybe should keep it down from the top a few inches.

Correct me if I'm wrong, but isn't the charcoal canister for fuel vapors?

correct,vapor in the fuel tank on a non vented fuel tank. On my 72 there is a hose that runs from the top of the tank to the canister, when the engine is running I believe vacume pulls the vapor through the can and into the intake. I think I'am overfilling the tank and causing gas to fill the canister and discharging out of the can overflow hose onto the floor.The canister is close to the headers and exhaust.

Well that makes sense, but I'm sorry I don't know if that is the probem. You didn't have the tank or anything major in the fuel system out did you?

No I haven't, its only happen twice that I know of.When I picked up the car when I bought it, the previous owner was nice to fill the tank.When he started it for the last time it puked about a quart on the garage floor, and on sunday when I filled it maybe a half gal.past the click stop. Drove it home, half hour later notice gas on the floor. owned this vette going on three yrs now.

I've seen this come up on the corvetteforum website, it's a common problem. That's probably why my car smells like gas after I fill up, expecially in hot weather when the cold gasoline expands in the tank. Joe

I got to thinking about this problem over the weekend and what may cause this is a stopped up fuel tank vent. As fuel sloshes around it creates pressure with the cap on. If the normal vent is stopped up then it has to release pressure somewhere and it would possibly backing the fuel and pressure through the vacuum line. Its kind of like siphoning a tank. The pressure exiting the tank through the line leading to the charcoal canister create a vacuum once all the air has exited and starts to pick up fuel like a siphon.

Maybe?

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My gas cap is non vented,in reality the charcoal can is the vent,only happens when I fill the tank to close to the filler opening.Burn a couple gals. and no gas on the ground.

Hey guys,

I just stumbled upon this thread and thought I would ask a question. I have an '80 L-48 that wreaks of gas when it is hot outside. Do any of you know if the '80 model had this infamous charcoal tank that you are discussing? Sorry to hi-jack the thread but since you guys are discsussing this very tank, I thought you would know.

CVT4ME

|UPDATED|7/1/2003 10:00:52 AM|/UPDATED|


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http://www.photohost.org/gallery/data/3345/2118curb_2_small.jpg Crash

I'm not totally sure, but I think all 71 through 82 C3's had a charcol cansister (aka Vapor Canister. I'm going to take a gamble and say that its probably in the same place on your 80 model as my 72. Its located behind the Left side (drivers) front tire inside the open fender area. Look inside your fender gill and you may see it. You can access it from under car. There should be three or four bolts that can be removed that will drop a splash shield down and give you access to it.


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should the gas cap be vented? If not wouldent the canaster pull fuel from the tank with the vacum from the motor..........

The canister pick up at the fuel tank should be above fuel level.I believe when the tank is over filled, fuel is drawn to the canister.There is a overflow on the canister to prevent fuel entering the intake

I have an 80 and the charcol canister is located just as aftrshark says, in the engine compartment drivers wheel well area. I had gas smell from time to time. I found that the vacuum hose from the carb to the vacuum canister was never changed, soft, deteriorated and I suspected leaking. Changed the hose and no more gas smell.

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Going back a few years when I was a GM mechanic. I beleive that there was a valve inline from the canister to the fuel tank to prevent this from happening. Again it was many years ago but it seems to ring a bell. I might be wrong but then again I might be right :)

I will give this same line a look over as soon as the great state of Texas dries out. Hopefully I can get this one fixed, I am tired of the wife telling me that I smell like gas when I am done driving the Vette. Is there a life limit on the charcoal in the tank? Can the tank, or its innards, be replaced if need be?

CVT4ME

|UPDATED|7/7/2003 8:47:18 AM|/UPDATED|


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http://www.photohost.org/gallery/data/3345/2118curb_2_small.jpg Crash

I was flipping through my Corvette Central catalog earlier today, spending some more money I don't have, and saw where their were certain years of c3's that had an inline check valve. I think it was for 78-80 models. I'm curious is all C3's had this valve and no one happens to be making the other years? I wonder if you could put this inline valve on all years just as a precaution?

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I had this problem on my 73 and found that the vacuum actuated valve on top of the cannister was leaking and therefore not purging the fuel vapors. Consequently after a sufficient amount of vapors had condensed in the cannister, it would overflow and smell. I fixed it by regluing the valve. Hope this helps.

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1973 L-82 4 spd

I have a good article on this problem that was published back in '99 from the NCOA newsletter. Pat Goss wrote about the problem with topping the tank off at the pump & what happens when you do. Mainly he said that liquid gas fills up the canister and over flows into the engine compartment possibly onto the exhaust system. He also stated that having liquid gas in the canister could cause the Check engine light to come on, Car to run poorly, and fail emission testing. Also said if the canister is flooded you would probably have to replace the canister. This was a one-page article if anyone wants a copy give me a fax number and I can send you a copy. Unfortunately I do not have this for E-mail. Went to the NCOA home page but could not find this article anymore.

If you would be so kind to fax it to me at 210-207-3393. That would be great and thanks for sharing the info.

CVT4ME

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http://www.photohost.org/gallery/data/3345/2118curb_2_small.jpg Crash

I have a 72 convertible. I removed the tank to redo my rear suspension and found there is a valve on the tank that is to prevent, I believe, liquid gas from getting to the canister which is mounted in the left front fender. the valve is plastic and is not available repro from what I found. You can bypass the valve with no trouble, from what I have been told. I used epoxy on my valve and also redid my canister. The filter was caked up after thirty years of road dirt.
I smell a hint of gas after a fill up but I believe it may be my cap. The gas tank is to be vented, if not the tank will sunk in. Happened to mine

I believe the cap on a 72 should be non vented,After Shark saw a valve in Corvette Central for 78 to 80, don't know if its the same or if it,will work

I believe it's safe to say that any system with the charcoal cannister has a non-vented cap and tank. That's the way they control evaporative emissions. The car burns the vapor created by evaporation when running and the charcoal absorbs the vapor when not running.

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1973 L-82 4 spd

Any idea as to when they started installing the charcoal canister? I have a '69 that seems like it smells most with a fresh tank of gas and the smell isn't coming from under the hood. I've yet to locate any kind of leak or seepage and it almost seems like the smell is coming from the mufflers????

I don't believe I have a canister and I feel that its entirely possible that I'm running on the rich side.



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'69 350/350 conv.

71 for canister and non vented cap, you should have a vented cap and a overflow hose connected to the rubber collar around the fill pipe that runs to the rear bumper.Bad cap, split rubber collar,rotten overflow hose will allow gas to run down the tank and onto the mufflers when a full tank with a bad cap is present. Look for gas stains on mufflers. had that above problem with my 72

anips said: Has anyone had a problem with fuel leaking out of the charcoal canister after filling the gas tank full? Maybe should keep it down from the top a few inches.

The check valve is called the liquid separator valve and depends on the year C3 year determines the configuration. Early years had it mounted at the front of the tank while later years had it mounted on the top. It is a large ball bearing that floats in a cage (late years).

Also in later years to make it work more effectively, a filler gas tube was included in the fuel sender assembly to increase pressure as the tank was filling so the gas pump hose would cut off without overfilling. This became a major problem on C5s and owners were instructed not to overfill...yes C5s. Owners still haven't learned! In the 70's, GM didn't drop owners a note like they do today.

With the non-vented cap in place, the system is pressureized...unless there is a vaccum breach. It sounds like perhaps the problem is several things, overfilling, a breach in the hose system and perhaps a faulty liquid separater valve...though I've never heard of them going bad. If it puked...even overfilling should have prevented this in a normally functioning system...that's my take tho there may be others.

However, I'm not sure what year the originator (anips) of the thread has...in the mid-years (C3) these systems changed more so than in later years.

The canister is the core component in the ECS or Evaporative Control System which captures fuel vapors when engine is at rest from tank and carb, holds them until engine is running and then recycles them for combustion. It operates off engine vaccum and therefore it is critical for effective operation all components be in place, no plugs and no breaks in vaccum continuity. First required on all cars in 1971, California cars came equipped with ECS in previous years.

73shark said: I believe it's safe to say that any system with the charcoal cannister has a non-vented cap and tank. That's the way they control evaporative emissions. The car burns the vapor created by evaporation when running and the charcoal absorbs the vapor when not running.

More emission control minutia:

The C3 model generation experienced the evolution of the 21st century gas cap and it evolved through three phases. In 1968 and 1969 we saw large-diameter gas caps with the word “VENTED” stamped into the cap. In 1970, the large-diameter caps have the words “SEALED” and in 71-72, the words “OPEN SLOWLY CAUTION” stamped onto caps. What we saw between 69 and 70 is the preparation for ECS. Tanks were pressurized to reduce fuel vapors that were once open to the atmosphere and therefore in 1971 contained within the vehicle to meet federal emission requirements.

In 1972, fuel tanks and their containment system were strengthened to manage the higher internal pressures. Tanks, straps and caps were designed to handle these higher pressures. So a 72 cap will work on a 69 Corvette but an early Corvette gas cap is not designed to handle the increased pressures inherent in post 72 Corvettes. Early pressurized caps were designed to sustain 1-2 psi while later caps were capable of handling ??? psi.

The third generation gas cap came in 1975 when the "restrictor" plate was added to prohibit owners from using leaded fuel along with the smaller opening. This is the system that is used in C5 and eventually C6 Corvettes.

BTW...the canister also has a purge valve that permits the saved fuel vapors to be discharged to the carb air intake once engine is operating. This is located at the top of the canister and operates on vaccum.

These systems can be checked by using a vaccum gauge and see if they hold pressure. If the needle on the gauge purges...your system is breached!

Had this happen today on my '72. It's been happening for years if the tank was just filled, driven a few miles, & then stopped. Driving home I said I should check c3vr! Sure enough- 2 pages of good info.

Since all these posts are about 9 months old, did anybody get any definitve answers to their leaks??  My tank has been replaced with new hoses; stock gas cap; evap hoses in engine compartment are new.   Thanks...   

For those of you with a Haynes Corvette Manual, there is a very good description of this (part of ECS System) and basically says a strong smell of fuel is a tipoff that the system is not operating properly.  Some other highlights, a pressure/vacuum gasoline filler cap must be used.  Anything else can render the system ineffective and possibly even collapse the fuel tank.  Says to disconnect the fuel tank line at the Charcoal canistor.  Presence of liquid fuel in this line is an indication that the vent controls or pressure-vacuum relief valve in the gas cap are not functioning properly.  Has other troubleshooting tips also.

Both the fuel tank and the carb float bowl connect to the charcoal cannister.  This is a sealed system.  It's purpose is to prevent gasoline fumes from evaporating into the air.  The fumes from the bowl and the tank both go to the charcoal in the cannister.  This charcoal looks like, and in fact is, about the same stuff you find in fish tank filters.  As the air containing fumes passes throught the charcoal, the charcoal absorbes and stores the gasoline fumes.  It allows air to pass.  This way heat expansion will create pressure, and the cannister can relieve the pressure without haveing the gas fumes in the surrounding air.

When the car is started vacuum is applied to the cannister valve, but the valve is not yet opened.  When the throttle is opened, control vacuum is applied to the control valve, and manifold vacuum is applied to the cannister.  This pulls outside air into and through the charcoal.  This fresh air flow picks up the gas fumes, and dries out the charcoal.  The air and fumes is drawn into the engine and burned.

When the car is shut off, the process starts over.

If the system is plugged between the tank and cannister, the tank cannot vent.  This can create pressure or vacuum in the tank.  Either way is a problem.

If the sytem is clogged or open between the cannister and the engine, it won't purge.  Then the cannister becomes saturated with fuel, and you get a gas oder from the front of the car.  In time, the cannister can be damaged.

If you overfill the tank and the tank gets warm, the fuel can expand and you can get liquid gasoline dripping out of the cannister.

If the tank has any leaks or the lines have any leaks, the fumes won't go to the cannister, and you get gas smells from the rear of the car.

Sometimes the valve assy will fail, and can cause all of the above, depending on the failure.  It can also rupture the diaphram in the valve and suck fume and fuel directly from the tank.  This creates a very rich condition.

The valve assy can be part of the cannister, or remote, depending on the year and engine set up.
All of the cannister equiped cars should have a pressure relief sealed gas cap.  Non canister cars use the vented cap.
kstyer38423.8479166667

What do you guys know about an orifice that is supposed to be located between the tank vapor line and the cannister? Mine i know is missing, is there anything that can be substituted for a replacement? Will not having the orifice in place cause the engine to pull too much vacuum through the cannister?

I've got a question, also....the previous owner had the line going to the cannister pinched off on my '72. The plastic valve mounted on the left side of the tank (it's marked ac delco-Rochester) has the top nozzle broken off which I'm guessing went to the cannister. The intake nozzle (hose from tank runs into it) is not clogged, I ran compressed air thru and it's operational. Here's the question: the EEC system is no longer performing its intended task (filtering fumes), but can the valve still relieve pressure from the tank? As a precaution, should I get a vented gas cap? Thanks.

JR

[QUOTE=princered72]I have a 72 convertible. I removed the tank to redo my rear suspension and found there is a valve on the tank that is to prevent, I believe, liquid gas from getting to the canister which is mounted in the left front fender. the valve is plastic and is not available repro from what I found. You can bypass the valve with no trouble, from what I have been told. I used epoxy on my valve and also redid my canister. [/QUOTE]

When I replaced the tank in my 73 I found there is a plastic valve (on the drivers side, top of the tank) that is to prevent liquid fuel from entering the line to the canister.

In my case the plastic case was cracked and allowed fuel to drip down on the the muffler.

Since the valve is mounted at the very top of the tank I would only have this problem when the tank was full and the gas was sloshing around.

To fix the crack I too used epoxy.

Also, when I installed the new engine I did not run the line from the canister to the carb. I left the canister installed with the line running from the gas tank the canister, but left the carb line end open. This allows the tank to vent if needed. I have never noticed any gas smell either...

If memory serves me correctly, the valve in question is a float valve. Your float may not be floating anymore which allows the canister to suck liquid gas... which splashes into the valve when the gas tank is full.

You might be able to do away with the valve all together and plug the line to the canister (and remove the canister if you want). However, you'll need a vented gas cap or equivalent so that the tank is vented.

 

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1973 Coupe    


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There is also a paper filter located at the bottom of the canister. Mine was very brittle but intact and clogged from dirt,etc. Have not found a vendor who sells them. May have to fabricate one that will work.

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Mike

[QUOTE=82CE]There is also a paper filter located at the bottom of the canister. Mine was very brittle but intact and clogged from dirt,etc. Have not found a vendor who sells them. May have to fabricate one that will work.[/QUOTE]

You should be able to get that filter from most auto parts stores. I bought one recently, less then 5 bucks.