Bear with me friends. The vacuum valve located on the ignition housing has two tubes running to it (one from a "vaccum pump" and one looped to the "shut of valve" on the engine) . When the cam presses the valve (closed) the vacuum dosen't reach the shut off valve and the car runs. When the cam releases (pin opened) the piston, and vacuum is formed, this engages the shut off valve and the car stops.

These are all question by the way. Maybe someday I can teach you something .

Why would one configuration of the two tubes stop the engine and one not let it stop.

Thanks in advance

Your description is correct, that is how it works.

Apparently the valve is directional, I don't know why it was designed that way. I assume that in one direction the vacuum from the pump will tend to hold the valve in the closed position, while in the other direction the valve will open freely.

Great I am on the right track. So if the lines were not connected and left open the car would run? And if I were to reconnect the lines the car would stop?

Yes, the car should continue to run until vacuum is applied to the shut-off valve, then it should stop. If the "ignition" switch is working correctly; shutting off the key should open the valve, apply vacuum, and stop the engine.

I have to get the car running tuesday b/c I am a delivery driver. I have to order new ignition parts so I am going to run my car by using a screwdriver to turn the switch on and off. The switch I am talking about is the one behind the ingnition housing. Then the only problem with delivery is that you have to do things fast, run in and out. I just cant keep my car running. Who can? So I am trying to figure out a cleaver way to control the vacuum shutoff and you have been a big help. If you have anymore suggestion, since tomorrow is a workday, I would really be in you debt. Thanks so much.

The only suggestion I have (other than getting out and pushing the stop lever) is to connect a mityvac (if you have one) to the line under the dash and pump up a vacuum when you want to stop it. Otherwise, how hard can you suck?

I guess you could also leave both lines loose under the dash and plug them together to stop the engine. You will have to keep the vacuum supply line plugged with something if you want to keep vacuum to the rest of the car.

So if the vacuum line is open the car will do what? I do understand what you are saying though.

If the vacuum line is left open you will have a vacuum leak. It may affect door locks ventilation dampers and shifting. You should keep the line from the vacuum pump plugged, the line to the shut-off valve will not matter.

Thanks for all you help!!!

What about the swich now that is attached to the ignition wire harness. I notice that it has three positions. 0 1 2. I assume that 0 is when it is shut off? in position 1 does that engage the spark plugs? And what about position 2? Is that where the car in running?

Position 0 = Off

Position 1 = auxiliaries only (radio)

Position 2 = running or glow plugs (dash lights on)

Past position 2 = cranking the starter (spring return)

Can all of this be done by the switch itself w/o the ignition housing or tumbler?

Have you experimented with it?

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
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