THSCC Forums

I've googled this a bunch, and there are certainly a zillion pages telling me what a charcoal canister *does*, and a bunch more that say "mine went bad".

But I can't find any that discuss how you might test to see if it is bad. My factory manuals say "test it and see if it's bad". Uh, ok.

So, this rig has three in/outs:

-purge, goes to intake
-tank, goes to tank
-ambient coming out the bottom, goes to open air

It seems that all the check valves for this model are internal to the canister. I see that some other models have the check valves in the lines instead.

So, there should be something like "put a vacuum on the purge line, and the ambient should be sucking, and no pressure on the tank line. blow on the tank line, air should come out the ambient..." and so on.

Anyone know how to determine if they're bad? Replacement cost is $325. The car is worth about $500, and that's with $75 of groceries in the trunk.

Anders

_________________
Lina Racing: As Seen On Radio

Anders,

You will "love" this from a 1984 Datsun (Nissan for you young folk) 200 SX shop manual:

Testing is very high tech. Literally inhale on the various lines. In the case of our 200 SX there are a total of three vapor/vacuum lines. The vapor vent port (from the fuel tank vent line) and the purge port (to the intake manifold or some other part of the intake system) should "leak" when you suck (inhale) on them. The "control" vacuum port should not leak when you suck on it. From the Datsun picture it has a vacuum diaphram which controls the purge port so that the canister can be purged when the engine is running. The Datsun canister is cylindrical and has a "fiberglass" filter wedged in the bottom of the canister to filter the air which is drawn into the carbon chamber.

Edit to add: It is possible that you may need to suck on the "control port" in order to open the purge port valve.

Dick

_________________
Dick Rasmussen

FS 50 2018 Mustang GT

The Datson manual tells you how to check the one-way valves. My understanding of what most people mean when they say their charcoal canister went bad is that it has liquid gasoline sloshing around in it. If the one-way valves are part of the canister, then failed valves would be the cause and the sloshing would be the effect. Personally, I would rather shake the canister than suck on the line.

_________________
Marvin McBride
Spec Miata #62

Unless it is an OBDII car, just bypass it.

_________________
Rich
http://www.v8mongrel.com/

Or use a Mityvac...you should have one, Anders, since you have a stock TT RX-7.

Appreciate your advice. However, the title of the thread is not "how can I get around this?"

_________________
Lina Racing: As Seen On Radio

Yes, that's what I'm using.

Anders

_________________
Lina Racing: As Seen On Radio

If you insist...

Since you failed to post what car this is for, I'll go on general procedure for an OBDII car with electircally activated valves. Obviously, things such as resistance and electical valve checks will need to be found in your factory service manual. If they aren't there, there is very little you can do save for comparison to a known good unit.

Key off, on the purge line place a 1 bar vacuum. If the valve does not hold vaccum, there is your problem. This is most often the problem as the valves stick because they accumulate the gasoline vapors while they are closed and that causes them to stick as a result of the varnish. Using factory procedure, energize the valve and vaccum should reduce immediately. If not, again, replace valve.

If the vacuum valve checks out, then you need to check the tank line valve. You must have a fully functional gas cap that can maintain pressure per specs. The tank line valve should be tripped open at certain tank pressure by the ECU. This spec varies by car, so if you don't have it, there is little you can do except check the function of the valve in the following manner. Pressurize the tank and tank to canister line with nitrogen to .5psi. The only spec I can find readily is Toyota says that it should maintain pressure for two minutes. A leaking valve should be readily apparent. Again, if it does not, replace the valve. Energize the valve and make sure that the pressure drops.

Diagnosis beyond this requires IM240 type equipment I am afraid. At this point, you will either buy a new one or bypass it. Good luck. This sort of integrated emissions system diagnostics is not for the faint hearted (the reason I suggested that you bypass it).

_________________
Rich
http://www.v8mongrel.com/

Read page 15 of this.

_________________
Rich
http://www.v8mongrel.com/