shut off valve? - PeachParts Mercedes-Benz Forum

dunl · #1 02-13-2006, 10:21 PM

Okay, trying to diagnose my engine that refuses to shut off. What I need, is to know exactly how the shut off vale works in relation to the vacuum pump, and I'd like to know how this valve urns off the engine.

I think I remember seeing something about if I pull a suction on the proper line, the engine should turn off?

Hopefully, that will give me more to work from than just knowing that "you have a leak somewhere, try to find it."

Thank,
Dunl

PS. Treat me like I'm age two..... cause that's probably the level I will understand it at.

rhodes2010 · #2 02-14-2006, 12:13 AM

On my non-turbo 1980 300D the shutoff is at the back of
the Injection Pump, not on the top, on the very back.
Vacuum line should be attached there.
Might even be brown tube.

Take your vacuum pump (mighty-vac or other brand) and apply
vacuum to this connection (I usually unplug the brown tube from the rubber
part of the fitting and keep a small piece of tube handy for connecting my hand vacuum pump to either tubes or connectors).
Apply the vacuum while engine is running and it should shut off, only about
5 bars or 5 ps, not much to shut it off.
Now, connect the vacuum pump to the brown tube that was in this connection.
Restart the engine, turn the key to off, the vacuum guage should jump up
to about the 5 or so mark.

What this proves: if the engine shuts off with the hand pump, then the shut
off circuit is working, if it does not shut off then the device on the back of
the injection pump needs replacing. Other folks here can advise on that,
it does not cost much and is easy to install.
If the pump guage jumps up when key is shut off then the key circuit
works and nothing needs to be done. If the key circuit provides no vacuum
then you have a problem there, again, others here can answer that and it
probably has been answered. Do a search on key switch vacuum.

You asked one more thing: the connection between vacuum and shut off.
There is a vacuum line straight off the master cylinder line that goes to the key switch
to provide vacuum, on my car it is also brown. This one provides the vacuum
for shutting off the engine, don't cross the lines.
But make sure this one is getting a good vacuum feed. You can test that one too.

Take off the panel under the drivers side dash to visually observe the
two lines connected to the key switch.

dunl · #3 02-14-2006, 12:30 AM

That's the info I was looking for, thanks!

dunl · #4 02-26-2006, 08:01 PM

Okay, next question: Found the shut-off valve line, and replaced it as it wouldn't hold a vacuum. It was brow with a blue stripe. I also found the brown line that goes off the master cylinder line (completely brown, no stripe). Both connect to the key vaccum switch, but I'm not sure which one goes where, and you said not to switch them by mistake (yeah, yeah.....whoops.

).

Is the line from the IP shut-off valve closest to the ignition cylinder, or the brown line that comes off the master cylinder line?

Thanks,
Dunl

dunl · #5 02-26-2006, 08:57 PM

The correct answer is..............

The brown one with the blue stripe. I finally found that there are two other lines that come off the master cylinder line that are leaking ahead of the brown line, causing the vacuum to be lost before activating the ignition switch. I bypassed them all by hooking the brown line directly to the line that comes off the master cylinder line to feed climate, door locks, ignition switch, etc. Turns off great now.

Thanks for the help that was provided. On to other problems....

dannym · #6 02-26-2006, 09:38 PM

Instead of hacking your vacuum system why don't you try to fix it right.

I wouldn't advise putting your whole system off one vacuum line. If it was built to handle it this way it would have been done that way to begin with.
It's all in the manual:

http://skinnerbox.steaky.org/Service/W123/w123CD2/Program/Engine/617/07_1-150.pdf

Danny

dunl · #7 02-26-2006, 09:43 PM

Quote:

Instead of hacking your vacuum system why don't you try to fix it right.

That would be why I am moving on to the door locks, as I know one of those lines is leaking. Is there any danger to the shut-off valve from the way I have bypassed it right now?

dannym · #8 02-26-2006, 10:01 PM

You probably haven't found this yet:

Vacuum Diagrams

DAnny

dunl · #9 02-26-2006, 10:10 PM

I did in the past, but forgot about them. Unfortunately, the shut-off valve diagram doesn't show which line is closest to the ignition mech, but I got it figured out anyway. Would have come in handy a week ago, though.

I don't see a diagram for the locking assembly for a 116 chassis....any chance you have one of those, and could toss it into this post so I don't have a couple of threads going in the same topic?

diagnosing door locks

Thanks for the help!
Dunl

JimmyL · #10 02-26-2006, 11:45 PM

Quote:

Originally Posted by dannym

Instead of hacking your vacuum system why don't you try to fix it right.

Danny

It was fairly obvious that he was just hooking it up this way until he finds the leak that is causing the problem.

Turning the car off can be of some importance, after all.

Before you hop on someone quite that aggressively, you might consider all options.
Wow.....

whunter · #11 02-27-2006, 03:17 AM

Quote:

Originally Posted by dunl

That would be why I am moving on to the door locks, as I know one of those lines is leaking. Is there any danger to the shut-off valve from the way I have bypassed it right now?

This is a normal bypass, mechanics cheat this way while diagnosing vacuum lock issues.