I just noticed my gas cap seems to ""Woosh" when I open it: I am not sure if it is a pressure or vacuum woosh: I do know I could smell fuel quickly after I opened it this AM... Is the cap supposed to be vented, and what symptoms would indicate blockage if so?

Thanks!
Scott

 

Did you plug the vapor line/canister

 

I have the same issue. I'm not sure if the cap is vented but the tank should be. The tank vent may be blocked? I wonder if these trucks have a line that runs to a charcoal canister like on the 80-86 trucks? I am not worried about it enough to actually figure this one out.

 

Basically but I don't know if its a charcoal canister the hose runs to a vapor canister under the battery inside the engine compartment if the hose to is plugged it could do that

 

It seems to be the woosh is outbound- like the tank is pressurizing: something it has not done before... Enough so you can smell gas, and the threads of the gas cap are wet... I wonder if it may be, as suggested, a plugged charcoal canister or line thereto... Could it be something in the selector valving?(Twin tanks)

Scott

 

No- I haven't plugged any lines- I usually leave that stuff alone, or fix it...

Scott

 

Replaced the cap: no change... I am kinda suspecting the charcoal canister or the vapor return line: I have to go through the manual, but if it ports through the selector switch, that would probably be my first suspect...
Scott

 

Assuming this issue is on your 1991 F150 in your sig then you do not have a selector valve. The vents are tied together then routed to the charcoal canister. The Canister Purge (CANP) solenoid is activated by the computer to allow the fumes to be drawn into the intake plenum.

Some reading from the Ford Service Manual to cure insomnia:

Fuel Evaporative Emission System

The evaporative emission system limits the amount of fuel vapor a vehicle may release to the atmosphere, enabling the vehicle to meet current federal and state requirements for fuel evaporation. The system works by capturing a very high percentage of fuel vapors that might otherwise escape from the gas tank. It then directs these vapors to the carbon canister where they are stored while the engine is not running. When the engine is running, and conditions are acceptable, the vapors are purged out of the canister and into the engine. This "clears" the canister and allows it to accept more fuel vapors the next time the engine is shut off.

The system is basically the same for all vehicle and engine lines: a hose or tube runs from the top of the fuel tank to the carbon canister to allow fuel vapors to pass from the tank to the carbon canister. A tube or hose runs from the carbon canister to the engine, allowing vapors to be purged from the canister. Some engines use additional valves in one or more of these lines to provide additional control over how much or when fuel vapor will be allowed to pass.

 

Wonder if the computer is not triggering it? Additionally, I found the fuel cap does have a built in pressure relief when it reaches a certain pressure... I'm still researching the thing, but may trace those evap lines, and check for a blockage.

Thanks!
Scott

 

I recall my old 1992 F350 would pressurize the tanks when I filled up in the cool evening then drove during warmer weather in the day time. It was sporadic so I never gave it a second thought.

I do not recall if either of my 1993 Lightnings did this or not.

 

Run the KOEO tests, see if you get a CANP related error. Code 565 or equivalent two digit Code 85.

 

I may give that a try at lunch time...(I keep the reader aboard... lol...)

Thanks!
Scott