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Message: [QUOTE="Strictly Diesel, post: 857799, member: 1411"] You have to remember how the regulator in one of those pumps is "supposed to" work (I say that because sometimes the adjustable regulator in the ADII has problems with severely leaking O-rings which throws "supposed to" out the window). These regulators don't control volume, they simply control pressure when enough volume and sufficient restriction in the main flow line are available. If the pump moves more fuel (GPH) through the main outlet (to the high pressure pump or directly to the engine...depending on the setup) than the next component can move, there will be a pressure side restriction. This is where the pressure comes from. If the volume (GPH) from the pump is high enough, the pressure will exceed the point at which the internal regulator (in the pump) opens. This happens to allow fuel to escape the circuit (reduce the GPH going forward) and thus reduce the pressure. If there is not enough fuel volume (GPH) to make enough pressure to open the regulator, the regulator will remain closed and do absolutely nothing. So, to answer your question... If you turn the pressure down on the ADII, the regulator (if working properly) will relieve pressure from the fuel supply stream leaving the pump IF AND ONLY IF the pressure in that line exceeds the regulator set-point. In order for that to happen, the ADII will have to move enough volume of fuel (GPH) to exceed the volume of fuel the stock pump (in this case) is moving, and the excess volume moved by the ADII will need to be high enough to build enough pressure to open the regulator. If the volume isn't there, the regulator should never open. Numerical examples (illustration only): Stock Pump Flows 40gph ADII Pump Flows 40gph In this case, the ADII should supply sufficient fuel volume to keep up with the stock pump, but the pressure at the inlet of the stock pump will be 0psi. The ADII regulator should remain closed because there is no reason for it to open. Stock Pump Flows 40gph ADII Pump Flows 80gph In this case, the ADII moves 2x the volume of fuel that the stock pump can. There WILL be pressure at the inlet of the stock pump because the volume being supplied by the ADII is greater than the volume the stock pump is transferring from the inlet to the outlet. In this case, depending on the adjustment of the ADII regulator, there should be fuel being bled off by the ADII regulator. Does that make sense? [/QUOTE]