what is the primary function of the fuel tank check valve? Where is it located on the car? What happens when the valve goes bad? Could a bad check valve cause a hard start/no start condition, Vapor lock or cause all of your fuel pressure in the rail to leak back to the tank? Is the return line also routed to this valve?

 

It is there to keep the pressure in the lines when the car is running. It should hold pressure in the lines for 30 minutes after you turn off the car. If it is not working then yes, it could cause hard starting problems.

Where is it? I have no idea but I am sure the FSM is online somewhere. I think www.fc3s.org has it.

 

Fuel fumes reduction device:

 

the check-and-cut valve enables fuel vapors to go into the charcoal canister and allows venting of the fuel tank ...

see
http://www.geocities.com/huguesdc1/evapcrank.html
for more info.

If you think there is a problem with your evap system, disconnect the line going from the purge valve to the intake (the one after the plates), cap the port you just created, and stick the line into a reservoir (catch can type).

that way you have put the evap system out of the equation along with the crankcase recovery system.

Hugues -

 

Another way to see the function of the check valve is that it zeroes (within some threshold) the pressure in the fuel tank ...

if pressure rises in fuel tank due to fuel vapors, the valve allows fuel vapors to go to the canister, relieving the pressure.

If vacuum forms in the tank, it vents the fuel tank to the outside ... meaning it draws air from outside into the tank to release the vacuum.

What you don't want is fuel vapors to be released into the atmosphere ... that would be bad for emissions and safety reasons, well at least to some people.

Quite a nifty gizmo !

Hugues -