Non-functioning Emergency engine shutoff valve
 

Originally I posed his question on the Diesel board, but it was suggested that i post it here. So here it goes.

My car is a '95 E300 Diesel. I bought the car two years ago and accidentally noticed that the emergency engine shut-off knob (The one on top of the fuel filter) was turned all the way to the "Stop" position. I did not understand how the engine was still working with this knob closed, so I turned it back to the normal position and then again to the "Stop" position. It made no difference, the engine kept on working normally.

I then disconnected a vacuum line, and turned off the ignition to simulate a vacuum leak. Closed the shut-off knob again, waited 5 minutes but the engine kept on running. I reconnected the vacuum line an the Engine immediately stopped.

I then unscrewed the Emergency shut-off knob (valve) and examined it. Its seals correctly and appears to work as intended. I also changed the fuel filter (original Mercedes filter) thinking perhaps the fuel filter into which the emergency shutoff valve screws was the wrong filter. I also changed the "O" rings. So far nothing.

Does anyone have an idea why the Emergency shut-off knob will not cause my engine to shut-off.

Thanks

Phil