A system and method of detecting the presence of fuel vapor gases within a fuel supply module tank. The system includes a lift pump for filling the fuel supply module reservoir with liquid fuel from the main fuel tank. The fuel supply module reservoir may include a certain amount of fuel vapor and air, which is detected by a pressure sensor. If a resting pressure is detected, a control module runs the lift pump to pump liquid fuel into the fuel supply module reservoir and purges the vapor and air from the reservoir.