I have an Lincoln Continental Mark V 1979. On the the ignition module (dura spark II) is a valve (vacuum modulator) mounted and controlled by the ignition module. What is the function of this?
The vacuum unit that is attached to the side of the ignition module was installed by the factory on certain vehicles. It’s function was to automatically adjust the ignition timing in response to altitude changes in order to prevent engine detonation and possibly to also maintain control of certain emissions. Keep in mind that this device was tailored to the fuel of the day. I do not believe that the exact new parts are available today. Your vehicle should run fine without this feature and with the ignition timing set to the fuels that we are compelled to use in our engines today. We should have such an ignition module available for you to use if yours is suspected to be defective. The two systems are shown and described in detail starting on page 23-01-02 of the 1979 FoMoCo Shop Manual.