An injection molding system for initiating flow of fluid material into multiple gates of a mold cavity during an injection molding cycle, the system comprising: a first selected valve comprising a first fluid flow passage having a first gate to the cavity, a first valve pin driven reciprocally along an axial upstream downstream path of travel through the first flow passage by a first actuator between gate open and gate closed positions, one or more downstream valves, each downstream valve comprising a downstream fluid flow passage (22A, 22B, 22D, 22E) having a downstream gate (24A, 24B, 24D, 24E) to the cavity disposed downstream of the first gate, a downstream valve pin (26A, 26B, 26D, 26E) driven reciprocally along an axial upstream downstream path of travel through the downstream fluid flow passage (22A, 22B, 22D, 22E) by a downstream actuator (30A, 30B, 30D, 30E) between a gate open and a gate closed position, at least one fluid property sensor (50A, 50B, 50D, 50E) mounted within the system such that the fluid property sensor detects, at a downstream detection time, a flow front (5R, 5L) of the fluid material flowing downstream through the mold cavity at a trigger location within the cavity disposed between the first gate and at least one selected downstream gate (24A, 24B, 24D, 24E), the fluid property sensor (50A, 50B, 50D, 50E) sending a first signal indicative of the downstream detection time to a controller, the controller receiving the first signal and including a set of instructions that instruct the actuator (30A, 30B, 30D, 30E) of the valve associated with the at least one selected downstream gate (24A, 24B, 24D, 24E) to open the gate on a first injection cycle by withdrawing the valve pin (26A, 26B, 26D, 26E) from the gate closed position at an instruction time, the instruction time on the first injection cycle comprising a predetermined open gate target time following the downstream detection time, wherein the valve associated with the at least one selected downstream gate further includes a position sensor that detects an actual open gate time upon withdrawal of the valve pin from the at least one selected downstream gate (24A, 24B, 24D, 24E), the position sensor sending a signal indicative of the actual open gate time to the controller, characterised by the controller receiving the signal from the first position sensor and including a set of instructions that automatically determines an adjusted instruction time (X') for use on a subsequent injection cycle, wherein the instructions that automatically determines comprises decreasing the time of instruction to the valve pin to open on the subsequent injection cycle by an adjustment time equal to any delay in time between the predetermined open gate target time and the actual open gate time. a first selected valve comprising a first fluid flow passage having a first gate to the cavity, a first valve pin driven reciprocally along an axial upstream downstream path of travel through the first flow passage by a first actuator between gate open and gate closed positions, one or more downstream valves, each downstream valve comprising a downstream fluid flow passage (22A, 22B, 22D, 22E) having a downstream gate (24A, 24B, 24D, 24E) to the cavity disposed downstream of the first gate, a downstream valve pin (26A, 26B, 26D, 26E) driven reciprocally along an axial upstream downstream path of travel through the downstream fluid flow passage (22A, 22B, 22D, 22E) by a downstream actuator (30A, 30B, 30D, 30E) between a gate open and a gate closed position, at least one fluid property sensor (50A, 50B, 50D, 50E) mounted within the system such that the fluid property sensor detects, at a downstream detection time, a flow front (5R, 5L) of the fluid material flowing downstream through the mold cavity at a trigger location within the cavity disposed between the first gate and at least one selected downstream gate (24A, 24B, 24D, 24E), the fluid property sensor (50A, 50B, 50D, 50E) sending a first signal indicative of the downstream detection time to a controller, the controller receiving the first signal and including a set of instructions that instruct the actuator (30A, 30B, 30D, 30E) of the valve associated with the at least one selected downstream gate (24A, 24B, 24D, 24E) to open the gate on a first injection cycle by withdrawing the valve pin (26A, 26B, 26D, 26E) from the gate closed position at an instruction time, the instruction time on the first injection cycle comprising a predetermined open gate target time following the downstream detection time, wherein the valve associated with the at least one selected downstream gate further includes a position sensor that detects an actual open gate time upon withdrawal of the valve pin from the at least one selected downstream gate (24A, 24B, 24D, 24E), the position sensor sending a signal indicative of the actual open gate time to the controller, characterised by the controller receiving the signal from the first position sensor and including a set of instructions that automatically determines an adjusted instruction time (X') for use on a subsequent injection cycle, wherein the instructions that automatically determines comprises decreasing the time of instruction to the valve pin to open on the subsequent injection cycle by an adjustment time equal to any delay in time between the predetermined open gate target time and the actual open gate time.