300D Vac Mystery (Have MityVac & Have Searched Archives...) - PeachParts Mercedes-Benz Forum

veg_burner · #1 05-02-2005, 04:34 PM

So all of a sudden the key won't shut it down; I figured I knocked off a connection, been in & out of the engine compartment numerous times lately. All connections were good. Coincidental to that the doors no longer lock. So I searched the archives: made sure I had vacuum off the pump, ~20" (brakes are fine). Put vacuum to the IP shutoff and it shut down straight away and held vacuum (though the linkage didn't move as described - I'd have suspected that it just needed to be lubed if not for the doors...)
It wouldn't shut off with the key when I plug directly off the booster line to the green line w/ yellow stripe.
The brown line won't hold vacuum with the key on or off.
Yellow door line won't hold vacuum.
Yellow reservoir line seemed to be holding what I was pumping.
This happened at the same time.
Like I said, I searched but I couldn't find anything that matched my situation. Lots of good stuff on checking the locking system & replacing the IP shutoff but it seems like I've got a couple things going on at the same time & since it all happened at the same time they have to be connected.
I'll try & search a little more but at this point my head starting to spin...

veg_burner · #2 05-02-2005, 04:46 PM

I should also mention that I locked the driver's door lock to seal off the downstream locking system but this had no effect.

veg_burner · #3 05-02-2005, 05:28 PM

Ok so I went through everything again. Disconnecting the line to the locking system and plugging the port in the four-way where it connects to allows the engine to shut down, though it takes a little longer than usual.
I will use an excellent previous post I found by psfred to track down the leak in the locking system.
One question, though: since locking the driver's door didn't help with shutting down does that point to that locking diaphragm?

mandrake · #4 05-02-2005, 10:41 PM

My 300D suffers from the same malody.

All I do to correct it is to spray a can of WD-40 type lubricant on the linkage assembly.

I keep an extra full can in the trunk.

diesel don · #5 05-02-2005, 11:23 PM

Every time I've had that problem, its been a door lock or fuel door lock or trunk lock. Occasionally I have knocked something loose, but you've checked for that.

Normally it seems really wierd at first like there are 100 different options all converging. But usually it traces back to either the green or red line on one of the vacuum actuators. What I mean by that is that the actuator itself is bad in either the open or close port. Therefore, you simply begin by plugging one door at a time. Note: I usually suspect one of the back doors or the passenger front. Its relatively easy to plug those doors with golf tees.

Once you find it, it seems so easy.

Hey, at least its not electrical....

Don

dmorrison · #6 05-02-2005, 11:59 PM

Your brown line IS the shutoff "circuit". It should hold a vacuum depending on the position of the key. I would start with that circuit and find if everything on the brown circuit is operating normally.
You can isolate the door circuit by disconnecting and PLUGGING the yellow base lines at the firewall. Golf tees work well. If after isolated, does the car shut off, if no then it is not the lock circuit. Then do the AC lines. Same proceedure. By isolating the two systems in the cabin you cut down on a lot of searching.

Dave

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