Which vacuum line is this?

[WannaWagon]

I found a hard plastic vacuum line disconnected under the dash and couldn't figure out where it's supposed to be connected.

It is black and runs from the engine bay, through the firewall, and stops with a straight rubber connector on the end near the steering column. Under the hood, it connects with a T to a black box on top of the valve cover and to a flat disc-shaped section of the injection pump (sorry, but I'm new to diesels and still learning about the names of things on my engine!). What should this line connect to under the dash?

Thx in advance!

[JamesStein]

In my '84 and my wifes '83 300D... this line is taped in a bundle to the ingition kill vacum switch. Its also capped off. I think its a line to a gage that isn't installed on that particular car.

[Jimmy Joe]

on my car, there is a black line which attaches to a vacuum modulator on the IP. It is simply a vent line, and goes to nothing in the pass compartment. I don't know why it would be attached to a "t" in your car. The IP shutoff line is brown, and goes to the IP, from the ignition switch. Does your car turn off with the key?
Pics?

[WannaWagon]

I should clarify a little. The black line that I found hanging loose behind the dash goes through the firewall to a T fitting, which then splits off to the IP and the black box atop the valve cover. It sounds like the IP connection is the vacuum modulator you describe.

My car DOES turn off with the key, but there is about a 3 second delay between turning off the key and the engine shutting off. I have a couple other vacuum-related problems that I'm also trying to sort out (central door locking doesn't work, climate control is iffy), so when I saw this black vacuum line hanging loose, I figured that was a bad thing so I plugged it. Should I have left it alone? Should I unplug it now?

Sorry, no pics available at the moment.

[JimmyL]

Sounds like we are fighting a lot of the same stuff. My door locks don't work, but sometimes the back passenger door unlocks itself, or is hard to push and won't stay down (mostly when engine is running) Hard to find vacuum info and equate it to all the different places in the car. Always something to do....

Hello - this is my first post; I was waiting a while before I could be useful.


That vacuum line is connected to the proportioning valve on the injection pump. As the accelerator linkage moves, the valve "bleeds" off vacuum so that the correct amount of vacuum pressure will be supplied to the transmission modulator.

The black vacuum line that is open to the inside of your car provides atmospheric pressure to the proportioning valve. When you hit the accelerator, you decrease vacuum ( or increase pressure) - and that's where the air comes from.

So, don't worry about it; it's supposed to be like that.

[WannaWagon]

Thx, oil burner! Sounds like I better uncork that line or I'll have other problems.

[Carrameow]

This picture shows the Line.

[Carrameow]

[Carrameow]

Not being disrespectful, but are you sure?
I had a ton of vacuum problems last month and I finally sat down and studied the system carefully.
The transmission modulator has a black Line that runs all the way to the BLUE circular Transmission Vacuum Controller near the Fuse Box on the Driver side.
The connection is labelled "TRA"
I believe this vacuum controller 'talks" to the Transmission Modulator Valve on the driver side of the transmission.

The bleed/vent feature is actually for the attitude compensator which is the white plastic thing on the rear of the injection pump below the ALDA.

Finally look for heat cracked rubber vacuum connections on the Turbo, Transmission modulator valve, and EGR. Often the rubber hoses dry out in the extreme heat of this area.

Finally attach a vacuum guage to see how much vacuum you are pulling.

Carrameow,

You are correct. Minor variations exist between different engines and body styles, and because of this, it is important to figure out what line does what before making alterations. For example, my car doesn't have the blue vacuum amplifier near its fuse box.

On my car (617.951), the intake manifold line connects to the overboost protection device (mounted on firewall) and then runs to the altitude compensator (ALDA). Also, the proportioning valve is attached to EGR control. The EGR microswitches, thermovalve, and EGR valve itself can break, causing a complete loss of vacuum.


Here is a good website that explains a good bit of it:

http://www.continentalimports.com/ser_ic20242.html

[Carrameow]

Vacuum Lines have been driving me Crazy...now I know who to turn to for Help