Hi Guys,

Is this how the Fuel Vapor Canister works? Fresh air allowed in only when the Solenoid is moved out of the way and is in the process of purging? The manual says if you can blow into the tank port and air comes out then your solenoid is bad. I have air coming out the air port when this occurs, however, if I apply vacuum to the purge side, it holds. something doesnt add up here???? This is for a 1989/1990 TPI system according to the parts book.

 

Part of the issue here is that GM changed how the canisters were filled and also purged. Over the years it changed many times. However, in the '90 - '92 time frame they were a very simple setup.

I know that the '92 canisters were basically a sealed unit with a vent on the top. Marked AIR (or is it VENT?).

The older canister had an open bottom with a filter on it.

In both cases as the fumes from the tank were forced through the canister the scrubbed air was vented.

Then when the engine was running and the purge was taking place the opposite occurred. As the fumes were drawn from the canister fresh air was introduced via either the AIR/VENT opening or the bottom filter.

RBob.

 

Thanks, the drawing is only for representational purposes, not accurate for where the vent tubes are located. so are you saying that the air intake should only be open during the purge cycle? if I blow thru the "tank" tube, should air come out the "air" tube?

 

It is always open, there is no pressure in the canister. In your picture above the left most tube is the vent, can just make out where it states "AIR." This vent is always open to atmosphere. I have seen them open as shown, or with a small cap over it that has a slot cut in the lower portion. Or a hose on it that goes to a T into the fender area. Then two hoses on the T, one going up and the other down.

But the AIR vent is always open.

Yes.

RBob.

 

Thanks again, this is confusing to me, because when fuel tank pressure builds up and the Fuel Tank Pressure Control Valve opens to let fuel vapors into the canister, wont the fumes pass right thru the canister and just go right to atmosphere (AIR) if it is always open? When I simulate this environment with the canister off the car, not connected, this is definitely what would occur. But the whole idea of the canister is to contain the fuel vapors until the solenoid is activated and the fumes should go into the throttle body, not AIR ? What am I missing?

 

The charcoal holds the gasoline fumes...

RBob.