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International Automotive Technicians Network
Re: P120F Fuel Pressure Regulator Excessive Variation
Posted to HD/Fleet Forum on 2/16/2019

Low fuel lift pump pressure with high supply side vacuum would indicate a restriction between the tank and pump. Low lift pressure and low vacuum would indicate a faulty pump or an air leak. The tests you have run result in a faulty FRP sensor (is FRP at 0.49 ... Login to read more.