Charcoal Cannister: Needed?

Evaporative emissions system from start to finish....


Code 85 CANP solenoid - The Carbon Canister solenoid is inoperative or missing.

Revised 11 –Jan_2015 to add warning about vacuum leaks due to deteriorated hose or missing caps on vacuum lines when the solenoid is removed.

Check vacuum lines for leaks and cracks. Check electrical wiring for loose connections, damaged wiring and insulation. Check solenoid valve operation by grounding the gray/yellow wire to the solenoid and blowing through it.
The computer provides the ground for the solenoid. The red wire to the solenoid is always energized any time the ignition switch is in the run position.

If you disconnected the carbon canister and failed to properly cap the vacuum line coming from under the upper intake manifold, you will have problems. You will also have problems if the remaining hose coming from under the upper intake manifold or caps for the vacuum line are sucking air.

Charcoal canister plumbing - one 3/8" tube from the bottom of the upper manifold to the rubber hose. Rubber hose connects to one side of the canister solenoid valve. Other side of the solenoid valve connects to one side of the canister. The other side of the canister connects to a rubber hose that connects to a line that goes all the way back to the gas tank. There is an electrical connector coming from the passenger side injector harness near #1 injector that plugs into the canister solenoid valve. It's purpose is to vent the gas tank. The solenoid valve opens at cruse to provide some extra fuel. The canister is normally mounted on the passenger side frame rail near the smog pump pulley.

Connecting the gas tank vent line directly to the intake manifold will result in fuel vapor being constantly sucked into the intake manifold. There is unmetered fuel that the computer cannot adjust for. The result is poor idle and poor fuel economy.



It does not weigh but a pound or so and helps richen up the cruse mixture. It draws no HP & keeps the car from smelling like gasoline in a closed garage. So with all these good things and no bad ones, why not hook it up & use it?


The purge valve solenoid connector is a dangling wire that is near the ECT sensor and oil filler on the passenger side rocker cover. The actual solenoid valve is down next to the carbon canister. There is about 12"-16" of wire that runs parallel to the canister vent hose that comes off the bottom side of the upper intake manifold. That hose connects one port of the solenoid valve; the other port connects to the carbon canister.

The purge valve solenoid should be available at your local auto parts store.

Purge valve solenoid:



The carbon canister is normally mounted on the passenger side frame rail near the smog pump pulley.
Carbon Canister:

There is a small vacuum on the tank while the fuel pump and engine are running. The PCM can monitor this pressure reading and can supply vacuum to the tank through the purge valve by closing the vent valve at the canister. The purge valve usually gets activated at idle. The vent valve also gets used to supply fresh air into the system.

While sitting the vapors are transfered to the carbon canister and stored. When the car is idling the vent valve opens flowing fresh air through the canister and into the engine through purge valve...burning the fuel vapor along with metered fuel. This has a small affect on fuel trim at idle.

Carbon canisters are all 75 percent about emissions....and 25 percent about smelling fuel vapors when the car sits.

At the gas pump newer cars have a vacuum on the tank....when the cap is opened there is a release of vacuum. While filling with fuel the majority of vapor should be going into the canister. This is why you shouldn't force fill a newer car( filling past full ). The extra fuel will bleed into the carbon canister and can saturate the carbon.

As a matter of fact....a few manufacturers have had issues with the tanks collapsing because of the vacuum. ( Chrysler being one of them ). The tanks would deform causing wrong fuel level readings. That led to several people running out if fuel and vehicles cutting off in the middle of the road.

A lot of cars have sealed caps now...no check valve.

That's why when at idle the purge valve opens allowing regulated engine vacuum to pull vapor from the tank. The vent valve also helps maintain a steady vacuum by circulating metered air.

On newer cars the EVAP system is closely monitored and if anything goes out of whack it cuts the check engine light on. Even very small leaks will throw a code. The system checks itself every time the vehicle is started.

Makes the fox mustang canister system look primitive.

Too much vacuum on the tank will also cause the fuel pump to over work and can lead to early failure.

Our cars ( Foxes ) can run fine without the carbon canister. Our vented caps and tank breathers will keep the car from pulling too much vacuum.....but the fumes will build up in a small area.. like a garage. It has almost no affect on fuel mileage to remove it.

Some people coil about 3 ft of hose ( that would normally go to the canister ) and essentially make a vapor trap. Usually there isn't enough pressure to push vapors of of the coiled hose. It also causes some vapor to condense.

I leave the hose running up front on and tuck it behind the fender. I've never had a vapor smell issue. The hose rides back there with the end open. My car also lives outside. I've seen people put little valve cover filters on them to keep critters ( mud dobbers ) from building nests in the hose. If the hose is pinched off or plugged it can cause pressure to build in the tank.

Are charcoal canisters suppose to be sealed off with caps or wide open? Or are they supose to have some kind of vent caps on them. Reason im asking is cause i noticed my canister doesnt have caps on it. Not idea if it being uncapped is causing a vacum leak or not

Uhhhh ok so I just recently deleted all my smog stuff, pump, lines, removed all the stuff from the back of the heads and the charcoal canister is out to. Installed a new fuel pump aero 340. What do I need to do if anything about venting I guess? Idk now I’m all confused. Am I gonna blow up!!!!!!!

Reddevil91 said:

Uhhhh ok so I just recently deleted all my smog stuff, pump, lines, removed all the stuff from the back of the heads and the charcoal canister is out to. Installed a new fuel pump aero 340. What do I need to do if anything about venting I guess? Idk now I’m all confused. Am I gonna blow up!!!!!!!

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Honestly with a 340lph pump and the pressure it can possibly put out id reinstall the charcoal canister to absorb the vapours. But thats me.. Plus it would possibly benefit u to reuse the vapours from the tank so u can squeeze every mpg outta each tank lol. And depending on where u put the vent line. You might get baked off fumes unless u gdt a vented gas cap lol

The internal structure of activated carbon is extremely porous, things literally stick as they are going through, that is, if given enough contact time.
The term is "adsorption" with a D, NOT absorption with a B, and as you might guess from the name, capacity is limited.
Hence purging with fresh air, but carbon does not release everything, and even loads with contaminants from the "purge" air (think painter's mask)

It can be somewhat regenerated by heating to drive off volatiles, or washed in acid to remove calcium, bleached to remove sulfur, etc.
Note that some of the uses involve chemical reaction instead of adsorption, and these permanently degrade the carbon, aka used up.

Very easy to run that vapor trap hose as 3/8" or 1/2" and pack some carbon inside, copper or stainless wool packed in the ends to prevent migration and dobbers.
Fold a little fuel screen over the vent end and screw it somewhere (layed down the frame)
The slow movement of vapor up the hose provides ample contact time to trap scent, and the carbon restricts flow enough to keep it from being truly open.
This is how it might be done on farm machinery if fuel vapor PLUS hay-barn freaked you out. :-O


The rest of the thread was helpful, and I'm trying to contribute something. Thanks.

BananasCentral said:

The internal structure of activated carbon is extremely porous, things literally stick as they are going through, that is, if given enough contact time.
The term is "adsorption" with a D, NOT absorption with a B, and as you might guess from the name, capacity is limited.
Hence purging with fresh air, but carbon does not release everything, and even loads with contaminants from the "purge" air (think painter's mask)

It can be somewhat regenerated by heating to drive off volatiles, or washed in acid to remove calcium, bleached to remove sulfur, etc.
Note that some of the uses involve chemical reaction instead of adsorption, and these permanently degrade the carbon, aka used up.

Very easy to run that vapor trap hose as 3/8" or 1/2" and pack some carbon inside, copper or stainless wool packed in the ends to prevent migration and dobbers.
Fold a little fuel screen over the vent end and screw it somewhere (layed down the frame)
The slow movement of vapor up the hose provides ample contact time to trap scent, and the carbon restricts flow enough to keep it from being truly open.
This is how it might be done on farm machinery if fuel vapor PLUS hay-barn freaked you out. :-O


The rest of the thread was helpful, and I'm trying to contribute something. Thanks.

Click to expand...

Man I felt like I was back in anesthesia school learning about volatile agents and how the soda lime CO2 absorbers work on our machines.