My 1984 300TD Turbo won't shut off with the key anymore, so after researching the subject here, I took these steps:

1. tested the shutoff at the IP. It works.
2. the vacuum pump makes @17" Hg vacuum (520 mm Hg) at idle on the main line before the brake booster.
3. the brown shutoff line that goes to the ignition shutoff solenoid tested at 115mm Hg vacuum at the firewall. It tested at 200 mm Hg at the solenoid on the ignition switch. the brown line is on the outside nipple of the solenoid (don't know if this is right).
4. The brown striped vac line on the inside nipple of the ignition solenoid tested at zero mm Hg vacuum.
5. I replaced the ignition solenoid.

The engine still won't shut down with the key. Any ideas?

Are your vac lines to and from the ignition reversed?

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1989 300E 144K

It also sounds like you are quite lacking in the vac supply to the ignition. Double check the main line running between the pump and the booster, mainly the two circuit nipples that run off it (one should go to tranny and emissions, the other should go to the ignition and the cabin accessories). Make sure that these nipples arene't cracked or broke, namely the one closest to the firewall. That circuit should have 3-4 differnet lines split into it (ACC, locks, shutoff). Figure which one is your shut-off, and block the rest. If it shuts down with the key, you have leaks inside the cabin.

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1989 300E 144K

The brown one running from the IP to the firewall only gets vacuum when the ignition switch is turned off. The brown one that is hooked up with the other bundles gets vacuum all the time. Any leak in another system, lock, A/C, etc will affect shut down, or lack therof. MattB give a good description.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

I have tried reversing the nipples on the ignition switch in case they were reversed. Didn't work. I'll take a closer look at the 'T's and the yellow junction at the firewall to see if it's cracked, then try isolating the shutoff line.
Thanks

Progress! I isolated the shutoff line from the key, plugged the other lines and the Benz shut down -- a 7 second delay but it shut down. If I find and fix the vac leaks it should shut down pronto, like it used to?

Yep.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Traced and fixed a couple leaks and the Benz shuts down with the key -- pronto. I got a zero vac reading off the main line that comes off the brake booster. Is that normal? I can only guess that it must get vac when the brake is applied?

Many thanks to you two for your help!

It all depends what end your on...

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1989 300E 144K