PeachParts Mercedes-Benz Forum - View Single Post

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.