When I got my bus, the emergency flap solenoid was disconnected. When I inquired about it, the local DD dealer tech guy told me that there was a directive low those many years ago to disconnect it. Apparently it caused more problems by being accidentally activated than it solved. The injector springs referred to are actually the rack levers, not the injectors. They are mounted to the rack tube with a spring loaded joint so that if an injector gets stuck open all the other injectors can continue to operate normally, and return to idle or no-fuel. It's easy to tell - just take a valve cover off and see if you can move one lever without moving them all (engine off). My engine was updated to have the spring racks. Obviously, the spring rack solves the injector sticking problem but doesn't solve the run-away on oil problem which can only be shut down by lack of air for combustion, which the flap should do for you. The thing is, there are other ways to shut that sort of runaway down, like maybe a Halon fire system plumbed into the intake. The issue with the flap is that it is mechanically activated by a solenoid, and can activate incorrectly. Mine did it twice, causing a no-start till I figured out the flap was down, but if it happened at speed you would stand a great chance of blowing out the blower oil seals, and then when you fixed the flap and started the engine again getting the run-away from the oil being dumped in by the now-ruined blower seals.
Brian