I had defective nozzles in my fogger kit and fought problems similar to this, when the nitrous was activated it would pressurize the fuel system as well, I never noticed the gauge pegging because I was trying to watch the track and I would have to shut it off early because it didnt run right. Anyway this problem caused multiple broken gauges and leaking fuel pumps and regulators. The nozzles were missing a plug in them apparently, soft plume NOS.