My F150 is sucking air into the gas cap every 8-10 seconds while the engine is running. You can also make it do it if you push on the top of the gas cap. Is this normal or do I have a problem with the evaporative control system?

 

Without being a smartass, that's how a fuel system works properly. It needs a vented gas cap, air behind fluid, like a house plumbing to work well. Never noticed it to make a sucking noise but I'll be honest, I've never checked either.

 

Well actually I think that depends on the design of the system.

Do you know if the 1998 F150 XLT is vented through the cap, or is it supposed to be vented through the charcoal canister thats a part of the evaporative emissions control system?

 

You can just disconnect the rear canister on the 98. I did, back in in 04,-when it plugged, they quit making them for a time. Not sure if you can get one now.

Disconnect the vent tho, IF you go that route and not the solenoid. The fuel cap can be cleaned. I believe it is made to vent, but the odor runs to the charcoal filter. Suppose to, I've never smelled fuel running without.

 

What line to the charcoal filter can be disconnected? Do you have a diagram?

 

What, - do you think I'm Joe Diagram of something ???

Yea, I have one. See where hose #9 connects or the hose in back of #9 (vent solenoid). See how it runs to an empty compartment around the center of the tank.

There's a fine screen where it connects to the solenoid, behind it (#9). That screen plugs and seals the line shut.

Twist, pull the Orange cap at the connection. It will come apart eventually. If not, just break that usless thing. When it comes apart, you'll see the screen remaining in the hose end. -

 

Btw, that diag doesn't show everything, - or every hose. Some of it won't make sense, but that's the line.

 

Ok I'm not 100% sure I know which line I'm supposed to disconnect. The line that goes to #4 on the tank, or the line that just goes to that air box and connects into the back on the #9 solenoid?

 

#9 behind the solenoid, grab that Orange round connector, separate it there.

 

Here -

 

Great I'll give that a try to see if it stops sucking air in the cap.