Charcoal Canister leaking?

[betsy325e]

Hi everyone,

Still trying to track down high idle. I took the charcoal canister out today. Blowing through (with check valve disconnected) with one hose plugged I get air coming out of the bottom. I assume this bad boy is supposed to be a sealed unit, though there's a plate on the bottom with little holes in it, so I'm not sure if there's some allowance for blowby or some such.

I shouldn't be able to blow air through this thing with one hole plugged, right?

Thanks

[betsy325e]

follow up:

which end connects connects to the charcoal canister hose and which end connects to the throttle body?

http://c1552172.r72.cf0.rackcdn.com/20863_x800.jpg

[spdracrm3]

yes you will be able to pull air thru the bottom of the charcoal canister , during purge it will draw in fresh air over the charcoal pellets inside which draw off the stored fuel vapors and burns them . if it was plugged solid it would draw the system including the tank into a large vacuum and tank would collapse inward (not good unless you want a smaller volume tank) . the purge is basically a metered leak that when activated off idle will draw in vapors if they are present if not it just draws in fresh air, the "leak " is calibrated and controlled by purge valve.

the arrows on the purge valve go to the manifold (vacuum side ) . with valve dis-connected make sure you cant suck air back thru valve on port opposite side of arrow (this make sure valve is closing/sealing properly)

[betsy325e]

Thanks. I know I read somewhere that you should be able to check it for holes by blowing through it, but thinking about it at work today, I thought it made sense to add air before it goes in the manifold. Probably a stupid question on my part.

Best reply I've gotten since joining. Thanks again.

j

[betsy325e]

Still confused because I'm an idiot.

http://c1552172.r72.cf0.rackcdn.com/20863_x800.jpg Let's stipulate that:

Left hand side runs to manifold. Right hand side runs to canister.

Bentley says blow into "larger" port (I assume that means the right hand side to charcoal). No air should pass through. I got air passin' through.

Bentley then says apply vacuum to smaller side (I assume that means left hand side to manifold) and should be able to get air through. I get air through.

Air only flows one way through this mamma jamma. Which makes sense to me intuitively, but according to Bentley (and Haynes) this mamma jamma is junk.

Can someone explain to me the actual wtf physical science of what's happening here?

If I can suck air through from the manifold side, isn't this thing just constantly sucking air in during idle/at start up? Isn't that bad? I thought the whole point was that it's only sucking up the stuff in the canister while you're driving down the road.

Yes, I'm an idiot.

[spdracrm3]

your not an idiot ,its just hard to understand
so it works like this ,when you park a car in the hot sun the fuel in the tank heats up and vapors are created (the EPA doesnt want those unburned hydrocarbons to escape to atmosphere creating Smog) so as the fuel heats and expands it creates pressure this pushes the vapors up the line to the charcoal cannister the vapors travel thru the charcoal pellets inside and are absorbed/stored in the charcoal and the air now scrubbed clean of fuel vapors escapes out the bottom of the canister thereby excess pressure is not built up in the fuel system . and in order to stop these vapors from just going up into the intake manifold and flooding the engine with excess fuel vapors the check valve/purge valve closes on the canister side not allowing these vapors up to the manifold instead they are forced thru the canister as mentioned . (if you have a car that wont start after filling the fuel tank or acts flooded ,then this valve is the likely cause ,it has failed and is allowing vapors/fuel as tank is filled into the intake manifold causing flooding condition)
now when you start the car and start driving it we now want to purge those fuel vapors from the canister we do this by applying vacuum (off idle,ported,no vacuum is applied at idle) as throttle opens it uncovers the port that the purge line is connected to and vacuum is applied to the purge valve it opens and allows fresh air to be draw into the bottom of the canister and over the charcoal pellets in doing so it picks up the vapors and they travel up to the manifold and are burned .
so the valve you have pictured is a one way valve activated by vacuum on one side allowing air/vapors to flow thru ,and with "no" vacuum applied it should not allow airflow/pressure thru from cannister side . in later model cars this is done with an electric purge solenoid valve which can still fail.

so if you suck on the small port side (arrow points toward) you should get flow , if you blow thru large port it should "not "flow, sounds like yours is bad (dont blow to hard it only holds about 2-3psi,it just a spring loaded diaphragm that 18" vacuum can overcome but 1-2 psi wont open)

[betsy325e]

spdracrm3: Thanks for your explanation -- Seriously. I hate when I'm trying to troubleshoot and a book says "that's no good, chuck it" but I don't understand why.

1. I guess I was figuring the blowing went hand in hand with the vacuum being applied. It makes complete sense that with pressure from the tank building up you clearly wouldn't want it to be able to "blow" through.

2. I completely forgot about that port! Goddamn. You just blew my frickin' mind. And I cleaned that port so carefully not two weeks ago. Well done, sir. Dope slap applied to forehead.

I've been looking for vacuum leaks for like a week now trying to get rid of my high idle and must have gotten it in my brain that EVERYTHING is under vacuum at all times. I couldn't wrap my head around why it wouldn't apply at idle. Got it now. haha.

(see points 1 and 2 for evidence of idiocy.)

Valve = shot. Makes sense. Thanks a bunch.

J.