Problem in changing Fuel Metering Valve change in Mark Vie control system

Hi All,
we have 3 Turbine Generators which are controlled by Mark Vie.
we were using whittaker Fuel Metering Valve C422845-A4 in Mark V control system till 2016.

With Mark Vie, came new FMV C422845-C2 and Whittaker make Motor controller C450305.
Recently, the FMV failed. So, we replaced it with FMV of P/N C422845-A4.
Calibration and operation are perfect.
But in actual start, Unit is tripping in High Exhaust Temp.
Valve opening is more, so is fuel gas pressure immediate after ignition.

what is the difference between C422845-C2 & C422845-A4??
Is there any modification to be carried out in Mark Vie??

kindly help.