If you turn the key on and you hear a constant hissing noise coming from the intake its most likely the main injector oring is broken or the assistant injector is stuck open. Its possible the main injector is stuck open but highly unlikely. These are the only two components that allow fuel to enter the throttle body. I highly doubt the vaporizer is the issue. Main injector is the large circular one with an in line fuse. Assistant injector looks like a long 6 sided nut with 2 black wires sticking out the back.