Arnoud

Did not found any answer on this question with a quick advanced search, however I admit that I have not looked into the WSM on this yet (I'm being lazy today ) - anybody knows?

brutus

Never, it is purged of vapors as the engine runs.

Rob Edwards

They do get somewhat heavier after 20 years (Maybe dust and dirt via the 'vent' breather port?), but I've never seen a service interval for the canister.

Tom in Austin

Some cars have a filter for the breather port that is a service item but I don't think 928s have one ..

brutus

Maybe the old ones started out with more charcoal ??

17prospective buyer

Unless you constantly top up your gas tank to cram in every last drop of gas, they should last the life of the car. If you eliminate the approx. 12% air pocket inside the fuel tank designed to vent the fuel tank vapors to the charcoal cannister by topping up, liquid fuel can fill the cannister up. There is a liquid separator in the EVAP system though, but not for lots of liquid fuel.

brutus

Never heard of this. "If you eliminate the approx. 12% air pocket inside the fuel tank designed to vent the fuel tank vapors " Can you elaborate on the source ?

Arnoud

Thanks Brutus, Rob, Tom and 17prospective buyer for your reply answers.

The reason why I asked this question to begin with is as per the following (as a picture tells usually more than a thousand words):

I.e. due to the current ongoing overall car repairs (as ongoing after my accident from a while ago, once my insurance had agreed on full repair and a good place was found and approved by me) these kind of items are suddenly having amazingly easy access (I know: very dangerous slippery slope of a different kind of WYAIT... ).

@ 17prospective buyer: as per Brutus question, can you please further explain?

17prospective buyer

Elaborate on the source? Sure, every EVAP system requires a constant air pocket to function properly and purge fuel vapors correctly. The fuel cap also plays a role in the EVAP system as it can somewhat relieve vacuum through a sprung check valve built into the cap. The 12% figure is from my Fuels and Emissions instructor in college. When you fill the tank up there is always/supposed to be an air pocket so that the EVAP system does not get flooded.

There is a vapor separator located at the top of the fuel tank (the highest point in the fuel tank), it collects fuel and redirects it to the tank, but it is not designed to be constantly flooded with fuel. When liquid enters the vapor separator it lifts a float which then seals the passage to the charcoal cannister, when the fuel is drained, a return spring lowers the float and the vapor passage is open.

brutus

Ah theoretical not based on how a 928 is set up. The good sized liquid overflow tank (looks like a bed pan) serves that function. It is above the right rear wheel and set up to drain back into the tank. The vapor recovery is plumbed into this as well, also fuel tank air intake and the 928 fuel cap is sealed.

17prospective buyer

How can the fuel cap be completely sealed? It should relieve vacuum.