So a new issue has come up on my 79 240d. When I turn off the key the car wont shut off. So of course, I immediately went to the fuel shut off valve, tested it to see if it will hold vacuum and it did have asmall leak, so I replaced it with a new bosch replacement.
Installed the new one and still not shutting off. I started checking the lines with a vacuum pump and all seemed fine. I finally then took off the dash and check the two brown lines. Hard lines seemed fine, rubber hose seemed a little old, so I replaced that too. I hooked up my vacuum to the side that goes to the brown/blue line and then to the valve. I turned off the key and checked the gauge to see how much vacuum its pulling. Only pulled about 2-3 pounds of pressure, not enough to shut off the engine.
So at this point im pointing to the ignition switch. Am I right? If so, can that part be rebuild?

Could be just a vacuum leak in the rubber connectors/harf lines on the shutdown circuit, or other vacuum consumers (failed center pod diaphragm for HVAC, central locking system leaks).

Test by blocking off the other vacuum consumers, so only the shutdown circuit is hooked up.

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

It has good vacuum up until that point. I did hook up my pump the brown line just before the ignition switch with its rubber hose and had good vacuum. If I add the that shut down switch then that when theres a massive loss of vacuum.

I did bypass everything else, so the only thing hooked up while twsting is the brown solid hard line to the main vacuum teeing of the brake booster

That little shut off device on the ignition switch is available as a separate part. It's held on by two screws and can be replaced without removing the whole ignition switch. But check out the vacuum for the doors, climate control, brake, and engine separately so you know exactly where your problem lies. Or if you have more than one problem on a 40 year old car. That old line about throwing parts at a problem...

Yes, I have done that already and checks out good. Thanks for the input

Ok so its bad...
I used this video as a reference
https://youtu.be/JhS4AvD814o

Whats the part number or what is that one part called?

VALVE- DIESEL KEY STARTING, MB Part Number A0004600284.

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

Alec, thank you!

For reference:

#7 is the Ignition Switch

#11 is the part your replaced and on this part the only the solid brown colored line goes to the top nipple on the part and the bottom nipple gets the Brown with Blue Stripe line and it goes from that bottom nipple to the vacuum shutoff at the Fuel Injection Pump. If they are reversed it won't work correctly.

#1 is the Steering Colum Lock and there is a plastic cam inside of the Steering Colum Lock that is what actuates #11

#5 is the Lock Tumbler

#2 is the Tumbler Retainer Sleeve

#6 is the Seat Belt Switch

Attached Thumbnails

 

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84 300D, 82 Volvo 244Gl Diesel

Thabks for the ingo Diesel911, it is part #11 that I did order. Everything else is working fine. The video i linked above really helped narrie it down.

UPDATE:
Ordered the part from pelicanparts and yes it was that one little part causing the issue. My troubleshooting paid off