a fuel flow damper is used on a mechanical pump system as the pump speed changes with revs the damper restricts over fueling by returning extra fuel to the tank.
With efi there is a fuel pressure regulator on the fuel rail. The electric pump runs at a constant speed producing well over the required pressure. (usually about 2.5 to 3bar is all that is required ). What the fpr does is detect the over pressure in the rail and opens to varying degrees allowing the excess fuel/pressure back to the tank. Keeping the fuel pressure the same throughout the rev range no matter how much fuel is injected.
So in summary a high pressure fuel pump should allways pump at a constant flow with the excess returned to the tank by the fpr. Try another pump on it if you have one. Also check for current drop on the motor.
There are non return injection fuel systems out there with variable high pressure pumps but i dont believe the sierra lump to be one of them
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