I've gone so far as to plug the shut off system directly into the main vacuum line, so the only things hooked up were the shut off system and the brake booster (because I cant think of a way to block off that end of the line). Even then it didnt shut off properly (still wound down). I have replaced the shut off valves at the key switch and the injection pump, and both lines are good.

With the car running, I noticed pressing and releasing the brake pedal consumes quite a bit of vacuum (more than 5 inches), and the pump immediately compensates. Does anyone have any tricks to seal the brake booster end so I can test it or run without it to test? Thanks for all the help!

Larry----when i installed that valve, I had the air intake assy torn down to the turbo itself, and I did have a runaway, but placed a DVD case over the turbo, and it was shut off in less than 5 seconds. In that time, we got one injector line cracked, but by the time any fuel sprayed from there, the engine was off.