Thanks Sam for the diagram and identifing the vent line. Shorebilly, I remember reading either your post or your reply to one during my search. I will revisit. I will also isolate the two valves and see what happens. I do have some other things going on this weekend, but will dap into it some. I will repost with my findings.
Thanks Again.
Mike

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Mike

Mike,
In your “newer vintage diesel” cars, there are many possibilities as to which vacuum component(s) might be causing your problem(s)… and as I said before, I believe that you probably have 2 causes of vacuum loss and these could be in separate subsystems because they can interact with one another… especially if someone in the past might has drilled out one of the restricted “T”(s) that branches off the large, main, vacuum line between the pump and the brake booster.

You can easily waste a ton of time and effort and worse yet end up more frustrated and less confident in your ability to deal with what might now seem like “abstract” vacuum components and systems. It helps me to think of vacuum as the reverse of a supplied air system… and to quantify it just the same way. Another way is to think of a supplied air system as positive pressure and the vacuum system as a negative pressure. In reality, however, both are positive pressures in “absolute” terms… it’s just that a vacuum has less air pressure than atmospheric [or "gauge" pressure]... so a vacuum is nothing more than a pressure less than atmospheric [14.5 psi] and is expressed the same as barameter readings... in inches of mercury in reverse. E.G - 10" of vacuum is a higher absolute pressure than 20" of vacuum. I hope this helps.

After studying the vacuum diagram for the “Federal” 1985 W123 300D TurboDiesel [I hope you don’t have a CA car – and you didn’t say]… anyway I recommend you start by using golf Tees to isolate or shut off the “Remaining consumer” lines that branch off the 4-way or 5-way rubber vacuum connector… EXCEPT the line going to the “SwitchOver Valve”[#81] which is part of the engine/tranny/turbo control system that uses vacuum as an energy source and control signal.

“Shorebilly”’s THREAD, also dealing with a 1985 300D TurboDiesel model is:
Vacuum Devices, '85 300D-T and hopefully Brian Carlton and/or others will pitch in here soon.

The main help I can provide you from this point is to encourage you to “isolate” the vacuum subsystems and NOT jump around from one component to another just because someone guesses the problem is this or that. You will have to use logic and your hand vacuum pump/gauge and find those leaks and fix them and this will eventually lead you to one or more components that might also have failed. Thanks to the experience of others on this FORUM/THREAD, you will learn how to isolate and possibly do without the EGR system, a common source of problems… and other components having to do with the turbocharger with which I have little-to-NO experience [yet].
Be methodical in your approach… don’t jump around… AND ask specific questions of those on following and responding to this THREAD.

Howdy,

When I was having my major problem....engine would not shut down...

First I hooked up my MiteyVac to the forward most Vacuum tap on the Main Vacuum Line that goes to the Brake Booster......and then ran the car, found that my Vacuum Pump was working....I had 23+in hg.....

Then I connected that back up.....and hooked up the MiteyVac to the Brown Vacuum line as it goes to the Injection Pump Shutdown device.....ran the car....pumped the MiteyVac 1x and Engine Stopped....this proved that the IP Shutdown was/is in fact working....

Next, after reconnecting that brown line......I disconnected the other brown line that goes from Vacuum Source....a little trident looking connector....into the firewall....and to the ignition switch......ran the engine.....pumped up MiteyVac.....turned off ignition key.....had to pump the Miteyvac a couple of times and......engine shut down......proving that the Ignition switch was operating ...perhaps not as good as it should...but was working.....will renew the little vacuum valve on ignition switch sometime when I dig under the dash.

Then I disconnected the lines from the after vacuum tap on the Main Vacuum Line.....the one that the 4 way connector attaches to.....pumped up MiteyVac....had to pump a bunch as this goes to Vacuum Reservoir.....and then watched to see if it would hold.....it did.......therefore no major leaks in anything in this area......Shut Down, AC Climate Control, Door Locks.....stuff inside car or to the rear of the engine compartment.

Then I disconnected the lines from the forward Vacuum Tap, once again, this time I connected up the Miteyvac.....pumped it...and it would not hold vacuum.....proving that the leak was somewhere in the EGR system.....or under the hood......in the engine compartment

Then I hooked up the MiteyVac to each of the devices......where vacuum Supply connects to......pumped up MiteyVac......found that the Switchover Valve, that operates Turbo Boost dump......would not hold vacuum.....plugged this line where it enters Switchover Valve, Golf Tee,...and ran engine.....turned off, engine shut down......

Since I have removed all of the vacuum plumbing in this circuit......and eliminated their connections as close to the vacuum source as possible.....

This is the best that I can do for you, from here.....

Isn't Mt. Airy, MD near to Cumberland??? I am 40 miles West of Clarksburg, allong RT 50...sorta.....about 130 miles from Cumberland

Hope that this helps...
SB

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Diesels:
'85 300D, "Max, Blue Benz", 155K, 27.0 MPG
'84 190D 2.2, "Eva, Brown Benz", 142K, 40.2 MPG
'77 240D (parts car)
'67 Eicher ES 202 Tractor "Otto" (2cyl, Air Cooled, 30HP)
Gassers:
'94 Ford F-150, "Henry", 170K (300 Six) 17.5 MPG
'85 190E 2.3, 148K....Parts Car
'58 Dodge W300M Powerwagon (Flat Fenders) Less than 10 MPG