Ah the beauty of forums such as these! Spot on Travengineer. I'm too long on the 400's. I was referring to the Engine Limit Control trim valve on the EDFP, not the FFR. My mistake. Now I've actually had to look it up, I better give you the details. Full trim applied at altitude could in fact flame the engine out (assuming a failure in the STA circuit). To prevent this, there is a bypass around the trim valve that always allows enough fuel to maintain at least idle power. Each selection of "Gnd Start" on the ignition switches exercises the actuator within the fuel pump to the full bypass position. This function was introduced via a SB well after EIS of the engine. Experience showed that lack of use of the actuator meant when the functionality was required for engine limiting, often the actuator would fail to operate. Hence the mod.
Always good to have these discussions, helps blow out the cobwebs!