To Joetom,
Fuel flow could have been restricted for a long period of time.
Think of Spar or LP valve being in a position between open and closed, Engine will run Ok upto a point, but when FMV/FMU needs more flow than avail, problems will start, problems may be delayed a little with the head of fuel down stream of restriction, but problems on the way.
A spar valve in a position between open and closed most likely would have resulted in a (LH/RH) spar valve (actuator) disagree EICAS message when the actuator is not in the commanded position. A not fully open engine fuel shutoff valve would have been detected by the EEC.
Even in the very unlikely case faults would not have been detected, the most likely moment either of these valves would have malfunctioned is during engine start, the only time they are operated until they are closed at moment of engine shutdown. Both LH and RH side failing at the same time although not impossible, it is very remote.
During a normal engine
(auto) start, the spar valves are opened manually by the fuel control switches and engine fuel shutoff valves are controlled by the EECs. Although the fuel control switches are manually selected from cutoff to run position, the timing of engine fuel valve opening is controlled by the EEC, it keeps the valve closed until the engine reaches the appropriate speed.
If the valves were only partially open, and if (in the unlikely event) faults were not detected by the EECs during engine start, the problems would have certainly surfaced during the takeoff roll when fuel flow is increased to meet takeoff thrust demand, a much higher demand than the thrust adjustments during final approach. A scenario for
both spar valves to move away from commanded (open) position during cruise or approach has been discussed several times in this thread. Lack of evidence as to how this could have occurred prevents that discussion from continuing at this time.
Green-dot