Question about fuel pressure indications, at fast idle 2200 RPM, fuel pressure is 42 PSI on EM2, if I switch on the back-up pump with the primary pump the pressure drops to 35 PSI, can here both pumps running, if I switch off either pump pressure goes back to 42 PSI.  My system is 13B, stock red injectors all four, pressure regulator is stock Mazda on the end of fuel rail with vacume connection from dynamic chamber.  Thanks,  David R. Cook  RV6A Rotary.