Door/Truck/Fuel Cap Unlock/Lock Diaphragms/Switches

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1. The first and easiest thing to do, is to try driving around with your doors LOCKED (or unlocked if you always drive around with them locked). And then see how it shuts off. If you can definitively say your car shuts off all the time when the doors are locked. (Or unlocked), this may be a $ufficient temporary fix! Hey- the price is right. By the way, this means that one of your locks, tubing, or diaphragms, has a leak.

1A. If you *REALLY* want to troubleshoot your vacuum system and find out which lock has a leak, you're going to have to get this:

Mityvac Test Kit - $64.95

Buy one @ Performance Products here,

With this, you will be able to test each SUCK and BLOW (lock and unlock)

Once you have figured out which one which one has the leak, a quick hack is to plug it up with a golf tee. This means of course that when you lock or unlock your doors, you will have to operate this one manually. But once done, you shouldn't have to get out of your car to shut off the engine.

There are two vacuum tubes running everywhere in the W123. In my car, they are yellow and green stripes on the tubes.

This is a great diagram showing the vacuum system from Performance Product magazine.

Vacuum system1.jpg

We'll deal with some of the most common trouble areas:

1. Each Door (1-2)

2. Fuel Door (In the passenger side rear door) (3)

3. The Trunk Lock (4)

If you take off your door, and sometimes you can see that the rubber has wore away and is no longer air-worthy. you can buy new ones, or buy a new one. Vacuumcontrolvalve.jpg $21-$28

Vacuum Control Valve - 123.133 - up to 036516 Left Front Door Master 3-Vacuum Line Conn. Note: add 1 x 116 805 01 14 Hold Down 1 x 116 805 02 32 To Latch VACUUM SWITCH

Master Vacuum Switch

Or it might be this:


You will find these in the bottom of each door, (Front/Right - Rear Right & Left) While you are looking at these, lock and unlock the door. You will see the white part move up and down, and you will see a little rubber diaphragm in there, if it's cracked, or you can hear it hissing, then you need to replace it!!!

These are about $35 each, and it's practically plug in play. When I replace mine, I will post some pics..



$35 new (what's the point of used?) I suppose you can buy these used, just to get by, but more often than not, they are probably in about the same shape as yours that just failed. They are all about the same age; really old!

Fuel Door: (Gas Flap Diagram)


Once you've troubleshooted this, or want to try something else, go back to the Dieseling Index

or try these:

2. Vacuum Tubing/3-way connectors/Valves

3. Shut-off Valve @ Injection

4. Shut-off Valve @ Ignition

5. A/C System Diaphragms

6. Vacuum Pump - Refurbishing

7. Replace Vacuum Pump

Or you can just get my syringe hack.