GTSIO Wf defect
It's been a long time since I've had my hands on one of these, but I seem to remember a similar defect. The guage is direct reading, so is actually measuring fuel pressure, not flow? Also seem to remember that there is MAP(?) connected to the indicator. If MAP is ok across range, problem must lie with pressure. So, if the engine is running ok, actual fuel flow is ok, then the pressure required to provide this flow must be less than maintenance manual specs. With my defect, the injectors were worn and oversize, so the fuel to the engine required less pressure for the same actual flow. I'm hoping you've already fixed the defect, (your post was a while ago) but this may be of some help. Did my head in at the time, was only a young bloke thrown in at the deep end!