Fuel vapor pressure in the fuel tank

[TTipe]

Just curious to know how folks respond to fuel tank vapor pressure. I don't believe any of the aftermarket calibrations deal with signals to open and close the vapor purge solenoid. Do people just open the fill cap every now and then. I'm installing braided fuel lines and wondering what others do with the fuel vapor line.

Thanks for looking.

 

[Raeban]

I am still running the charcoal canister and only open the tank when it needs fuel so I suspect my extender chip is letting the factory ECM do the purge or the fuel vapor isn't causing an issue.

 

[TTipe]

I am still running the charcoal canister and only open the tank when it needs fuel so I suspect my extender chip is letting the factory ECM do the purge or the fuel vapor isn't causing an issue.

I found a way around this if the code to drive the purge solenoid is not working the canister. Remove the seal from the fuel cap.

 

[Chuck Leeper]

I found a way around this if the code to drive the purge solenoid is not working the canister. Remove the seal from the fuel cap.

And then, the fuel sloshes out under accel??

 

[TTipe]

I have very serious doubts that fuel will slosh past the door in the fill neck and then through the shared threads between the cap and the filler neck. However the point is well taken. I was curious to see if any of these chips have eliminated the software that drives canister purge to salvage space for other code.

 

[buddy]

What about installing a Filter on the vapor line coming from the tank?

 

[hensleyt]

so its should not make that hissing sound when I remove the cap

 

[Raeban]

so its should not make that hissing sound when I remove the cap

The vapor is only released from a properly working vapor canister when the engine is at operating temperature, TPS> .75V and vehicle speed is greater than 5 mph. If you are hearing a hissing sound when you open the cap that shouldn't cause a concern.

 

[TTipe]

The vapor is only released from a properly working vapor canister when the engine is at operating temperature, TPS> .75V and vehicle speed is greater than 5 mph. If you are hearing a hissing sound when you open the cap that shouldn't cause a concern.

It more than likely makes a strong hissing sound when the fuel cap is removed because the fuel tank is not being purged for various reasons.

 

[Raeban]

It more than likely makes a strong hissing sound when the fuel cap is removed because the fuel tank is not being purged for various reasons.

One half dozen or the other as that depends more on the situation. There will always be fuel vapor with it sealed. The EVAP system was intended to store vapors when the engine isn't running, not stop any vapor from forming. The solenoid remains closed and does not allow any vapor to escape until the above criteria is met so finding vapor pressure when removing the cap is normal.

 

[pacecarta]

seems that some need to be educated on how the canister actually works
the pressure build up is not dependent on the solenoid activating
there is a pressure valve on the vent at the sending unit and the tank can build a few psi before the vent will open to allow excess pressure out ,also remember the vent also allows air in to replace the fuel that is used so the tank doesn't collapse

the vent flows excess pressure which has gasoline vapors and for emmissions that vapor can not be allowed to escape to atmosphere ,they accumulate in the charcoal canister, that canister is not a sealed assembly or vapor wouldn't enter it, (there's a large filter on the bottom ) . the charcoal stores the gasoline vapors and it remains there until the solenoid opens on deccel when it draws air through the charcoal canister allowing the engine to burn the stored fuel


excessive pressure could be a blocked vent ,its not uncommon to find the steel line blocked from rust and that can cause all sorts of drive ability issues

 

[Raeban]

seems that some need to be educated on how the canister actually works
the pressure build up is not dependent on the solenoid activating
there is a pressure valve on the vent at the sending unit and the tank can build a few psi before the vent will open to allow excess pressure out ,also remember the vent also allows air in to replace the fuel that is used so the tank doesn't collapse

the vent flows excess pressure which has gasoline vapors and for emmissions that vapor can not be allowed to escape to atmosphere ,they accumulate in the charcoal canister, that canister is not a sealed assembly or vapor wouldn't enter it, (there's a large filter on the bottom ) . the charcoal stores the gasoline vapors and it remains there until the solenoid opens on deccel when it draws air through the charcoal canister allowing the engine to burn the stored fuel


excessive pressure could be a blocked vent ,its not uncommon to find the steel line blocked from rust and that can cause all sorts of drive ability issues

When I mentioned sealed I was referring to the fact that vapors can't escape the system. Sorry if that caused any confusion.

 

[RmvBfrFlght]

The gas cap is designed to allow air to enter the gas tank, but not let vapors/air out of the tank. If the vent line becomes plugged or is capped off, the fuel tank can then build pressure.

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