What can cause an evap canister to clog?

[moribundman]

A friend's evap system started leaking fuel around the purge valve solenoid valve. He replaced the valve, because the car was idling poorly and he suspected that the valve was the cause of the leaking and poor idle. The leaking issue did not go away. Upon closer inspection he found out that the evap canister appeared to be clogged. What could have clogged it? Certainly not fumes, so it's reasonable to assume that gas got sucked into the evap system. The evap system should not contain any "wet" fuel, but only fumes, correct? Any idea what's going on?

 

[yugrus]

Any chances your friend overfills the tank by 3-4 clicks at the pump? That's how the fuel usually gets into the canister, as far as I know.

 

[moribundman]

I seriously doubt he's doing that. He's had the car for years and it's a recent issue.

Will the activated charcoal in the canister get lumpy or break down if fuel gets in, or could anything else have clogged the filter?

 

[Quest]

My understanding comes close to that of yugrus's.

The only way that would cause clogging on the charcoal evaporative canister would be mainly due to consistent overfilling, and or some gasoline quality issues.

Knowing that that particular canister is for trapping excessive fuel fumes from the gas tank during thermal expansion, and then when the time is right, the fume gets sucked back into the system for consumption, I cannot see why or how that canister gets clogged other than overfilling or due to some other external reasons.

Maybe it's a good time to pursue this investigation further?

 

[punisher]

Many cars also have a vapor separator to prevent just this type of problem. The problem is usually caused by chronic overfilling causing the mesh inside the cannister to shred and releasing carbon dust into the evap system. If chronic overfills are not the cause, find out if there ia a separator valve between the tank vent and the carbon cannister.

Sometimes cannisters just decide to let go. Probability says some have to be defective. It is rare, but I have seen it happen and it clogs the evap flow sensor (if equipped) and messes up the purge solenoid as well.

 

[Chris142]

It's even more fun when the charcol beads find their way into the carb......Not that common anymore I guess.

 

[Chris Meutsch]

Wow......I overfill every single time. At least to the nearest half or whole dollar. Perhaps I'll stop if this is true.

 

[alreadygone]

Difference between couple of clicks to top off and overfilling till it wont hold another gurgle.

Might ask if he's changed place of purchase. Sometimes ground slope at pumps can make a difference in how full different tanks will fill.

Bob

 

[Cutehumor]

ya, I used to do the same thing. fill to the brim. but lately the past year or so, I've been filling to round up to the dollar.

 

[moribundman]

I'll try to find out if my friend's car has a vapor separator valve. Thanks for the tip!

 

[moribundman]

FOLLOW UP:

My friend says there is a vapor separator valve attached to the bottom of the evap canister. He also said he's been topping off his tank lately because of the low price of gas. There you go...

 

[SHOZ]

On the older Taurus SHOs there is a check valve in the emissions line before the cannister. Over time it will get a waxy build up to the point it clogs the line. This has to come from the gasoline vapors as there is no way the gas itself can get that far up into the vent tubes.

 

[olddognewtrks]

I've got a general question while you're all here...
While on all day highway trips: If I fill it to the top, and then start burning off gas by immediately hitting the road, am I still asking for trouble with saturating my cannister? I've got an '03 Mazda Protege.

 

[Shaman]

Old, you shouldn't have a problem because the gas doesn't have time to expand before you have driven the top little bit off.

 

[Lonnie]

You should always try to get the last little bit of gas into your tank. And if you do, thank you for supporting your local garage or dealer. You can do it, just keep clicking that nozzle. It's easy and you can get a lot of extra gas in there, a pint or maybe a quart or more. If you quit at the first click you just a woose. You'll have a vapor recovery system that will last the life of the car, and that's no fun. Be a real man, keep clicking. Show the others around that busy gas station what a moron you really are.