More vacuum VOES

[pitofpity]

I've been driving with no issues with my door vacuum system disconnected. No discernable issues with the car engine stopping. I decided to fix the door vacuum lock issue and properly tested and addressed all leaks...at least I thought so. After diagnosing the leaks, I've done following tests:

1. Exposed the door master switch on the driver's side and tested all three lines (Yellow vacuum source, Yellow/Red locking side and Yellow/Green unlocking side). All three held pressure
2. Tested the Yellow/Gray line for the reservoir. It held the pressure really well.
3. Tested the check valve under the hood and it was sucking on the single port side.
4. Connected the Mighty Vac at the single port of the valve and built up vacuum which held well. I noticed that when locking/unlocking the car, the mighty vac would show a drop of 3" HG from 12” HG and flatten out upon further locking and unlocking.
5. When connecting the Mighty Vac to the yellow line under the hood and locking or unlocking, the pressure drops down to ZERO.

Here is the part that has me scratching my head, when the door system is connected and car is running over half an hour, the engine shuts down after 6-8 seconds. When the door locking system is not connected to the rest of the car and the rubber X connector is plugged off, the engine shuts off quickly. I am completely stumped of where the leak is considering entire door system is holding vacuum.

[Mark123]

So we know there is a smallish leak because the engine does shut off after 6 or 8 seconds. We know it is, in some way, the locking system. I would first check that 4 port rubber connector somehow. Like leave it on the door lock system, plug 2 sides, and test through the 4th. When I am stumped, it's usually because I left my blinders on and won't look outside my preconceived notion. What if there is a small leak on the door system and on the shut off that only shows up when both are charged? After I test the shut off and little switch on the ignition from under the hood, I would lift the driver side floor carpet and test left versus right. Then under the passenger carpet to test right front or rear. Passenger rear runs back to the fuel flap and trunk. Follow it. The larger the system the longer it may take for a drop in vacuum to show. Look for old,swollen rubber or oil. Check open and closing lines. Narrow it down. It has to be there and is somehow eluding you.
Then when I figure stuff out, I realize I should have been able to see it sooner.

[Popeye]

I'm a bit of a rookie with a gasoline W114, but a few ideas having just gone through my door locks:

Point 4: Vacuum dropping to 12" and then holding suggests a "self-sealing" leak, i.e. a rubber bit that moves enough when the vacuum reduces to be able to hold pressure. 12" vacuum is low. Perhaps a naive question reflecting my ignorance, however it would be interesting to test the engine shutoff vacuum at 12" of vacuum. Does it still work, or almost-work (explaining the slow shut-down)?

Point 5: I assume this is eliminating the reservoir from the circuit? If so, that seems normal. (Vacuum is lost each time the doors are locked/unlocked - thus the need for the reservoir, and the fact that doors can only be locked/unlocked so many times before the system stops working.)

In general, what I did to confirm my leak hypotheses was to eliminate the suspect components. In my case I suspected the trunk actuator, so I removed it and plugged both lines with rubber plugs that came with my mityvac (golf tees may work). I drove the car a few days and my door locks worked perfectly, confirming this hypotheses. In your case, find "easy" spots to break the vacuum lines, plug them and see what improves - again I am not familiar with the specifics of your car.

A second test I did was to compare vacuum levels locked and unlocked. In my case, the leak was on the "lock" side, i.e. if unlocked the door locks held vacuum, but when locked the quickly lost (<1 minute) vacuum.

...again, a few thoughts from someone who has only a few months of ownership experience. Smarter folks than me may chime in!

[pitofpity]

Culprit found! I unplugged the AC vacuum line and symptoms disappeared. Looks like my AC vacuum had a leak small enough not to affect the shut off without the door system being connected. With door system connected the shut off was affected. Off to another chapter of vacuum chase!!!