What would happen if you have no canister purge valve?

[mob]

Ok, weird question, I know for the evap system to function properly you need the purge valve to be intact. My question is sayyyy someone decided to take out the purge valve and run a vacuum straight to the manifold. What would happen? Would this cause idle issues? Would I be pulling constant vacuum out of the tank?

 

[jrichker]

Without the purge valve, the engine is constantly sucking fumes from the gas tank.

Several things are possible:
1.) Too much suction could cause the gas tank to cave in the bottom of the tank, just like someone tried to jack up the car under the gas tank.
2.) The engine will run rich from constantly sucking fumes from the tank.
3.) The fuel may flash boil in the tank on a hot day, since it will no longer pressurize correctly. Pressurizing the tank raises the fuel boiling point and insures a constant supply of liquid to the fuel pump.

 

[tmoss]

Huh? my tank has a rubber insert where the fill neck goes into the tank. How is that going to hold presure or vacuum?

 

[jrichker]

The tank is supposed to pressurize to about .25-.50 PSI: this keeps the fuel from boiling and insures a constant liquid delivery to the fuel pump.

For more information, see http://www.autoshop101.com/forms/h62.pdf. The specifics are for a Toyota, but the principles are the same for Ford.

 

[tmoss]

OK, but in reality you won't hold it with old/cracked inserts........

 

[jrichker]

OK, but in reality you won't hold it with old/cracked inserts........

Us old crackpots are surprisingly resilent.....