The return fuel has been heated, so more vapors than if no fuel return. But how much all those factors play off each other, I have no idea. I just know if you drive with the EVAP line plugged, your tank makes scary noises as it expands.
Shouldn‘t your fuel cap let air into your aux tank? Is...
No vacuum signal needed, but I’m sure it helps the delta and scavenge a bit. Pressure just builds beyond the small amount the check valve will hold. That way you don’t stink up you garage when the vehicle sits. My system works fine and it just vents to the atmosphere post charcoal canister...
If you pull the line off the separator and that relieves the pressure, it might or might not be the separator. That will definitively tell you if the tank is the issue. If no pressure is released, your tank is the issue. Possible, but not likely.
Since I’m lazy, I start at the other end of...
You don’t need to drill your fuel cap. You should fix the problem. Yes, the factory fuel cap lets air into the system. The EVAP let’s air escape. You’ll probably find the previous owner capped the line when he removed the charcoal canister. Try following the steps in post 5 below. You are...