How do diesel cars and other vehicles stop running when you turn off the ignition key?

I understand how petrol engines stop, by stopping the spark, inhibiting the ignition of the fuel. But diesel engines are run by compression of the diesel at a high temperature, so they don’t require an ignition source other than compression. So how does turning the ignition key stop the engine when its running? Does it stop the injectors from injecting fuel into the cylinders? If so, how were pre-injector diesel engines stopped?

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2 Responses to “How do diesel cars and other vehicles stop running when you turn off the ignition key?”

  1. CHARLES said:

    diesel cars have a solenoid on the injection pump that has a electo magnet .when you turn off the ignition a plunger drops to stop the fuel to the engine

  2. Bardic said:

    It’s just a matter of cutting off the fuel supply. These days there’s a spring-loaded valve which is held open electrically when the “ignition” is on, when you switch off the valve shuts itself.

    Previously you shut the valve yourself by pulling a knob, wire or lever which shut the valve.

    I used to wind up a colleague by leaving the cut-off knob pulled out, which he never noticed and wondered why the old van wouldn’t start . . .




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