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Message: [QUOTE="Strictly Diesel, post: 858300, member: 1411"] As a general rule, as pressure goes down, flow goes UP. So, to answer your question...NO. NO MATTER WHAT THE REGULATOR IS SET AT...the ADII pump is attempting to move the maximum flow through the outlet to the motor UNTIL the point that the pressure set-point is reached. ONLY when the pressure in the line between the ADII and whatever is after it reaches that set-point will the regulator open. The ONLY way the pressure regulator hurts flow is if it is STUCK OPEN, has damaged o-rings or is otherwise not working properly! If it is stuck open or O-rings are leaking, it creates a constant drain on the system that reduces the volume of fuel that is available to go forward to the engine. Otherwise, the regulator will only return the amount of fuel to the tank that is required to keep the pressure on the pump outlet at the set-point. If the volume of fuel being consumed by the rest of the system forward of the ADII goes up, the regulator will close to keep the pressure up, if the volume being consumed suddenly drops, the regulator will open to keep the pressure down. Either way, the pump is running at 100% duty cycle and attempting to push 100% of the flow capability TO THE ENGINE. Keep in mind that the only way to make pressure is for the ADII to move more VOLUME of fuel than the next component after it (the stock pump in this case). Since PRESSURE is what is required to open the regulator (if working properly), the only way the regulator will return fuel to the tank is if the ADII is moving more volume of fuel than the stock pump. I will say this...the ADII is the only pump on the market that can skirt the normal rules that apply here. The FASS pumps do not have any kind of internal passage for fuel, the fuel either goes to the engine or gets returned to the tank. In the case of the ADII, their "demand flow" regulator allows INTERNAL RECIRCULATION of fuel, which is why any failure of the O-rings on their regulator can result in a loss of pressure (fuel flows from pressure to suction side of pump, reducing the amount of fuel sent to the engine and the amount drawn from the tank), even though the pump may not be returning more fuel to the tank. I really dislike the fact that the ADII can and does allow an internal flow loop because this can be hard for some people to diagnose and it causes a LOT of phone calls to those of us making fuel systems because the first part people want to blame is our fuel pressure regulator. This is just one of the reasons I will NOT sell an ADII to any 7.3L or 6.0L customer...EVER! If you are running the ADII as the ONLY pump in the system, you are correct. The ADII needs to be set to a pressure HIGHER than what you want at the engine, so that the regulator on the engine can reduce the pressure and so that you have enough pressure overhead to keep the pressure up as demand from the injectors increases. The discussion above is different because I recommended keeping the stock fuel pump and using the ADII as a low pressure lift pump and filter setup, which should result is a longer living ADII. [/QUOTE]