Abstract: An engine shut-down circuit for a gaseous fuel induction system comprises a solenoid operated three-way valve connected to the electrical system such that when a shut-down condition is sensed, a vacuum signal from the intake manifold is sent to a pressure regulator, causing its internal fuel port to automatically close despite the presence of a residual negative pressure fuel supply signal which would otherwise keep the regulator open, thereby shutting off fuel supply instantaneously, despite continued rotation of the engine, thereby preventing fuel from being inducted into the engine which, if present upon restarting, would likely cause pre-ignition or backfire.