Howdy -
Here's a place to find your vacuum Diagram - http://www.peterschmid.com/ -
get yours and study it. But only worry about the part that controls the
engine - not the door locks and that stuff.
Basically, a vacuum pump on the front of the engine produces vacuum which
operate the power brakes, engine shutdown and some accessories. A vacuum
line runs between the pump and brake master cylinder area - there's a "T" in
the line which provides vacuum to the ignition switch. When the engine is
shutoff, the vacuum that is controlled by the vacuum switch pulls vacuum on
a "engine shutoff switch" located on the Injection Pump (often). When the
Shutoff Switch is actuated, fuel thru the IP is stopped so fuel no longer
reaches the cylinders thus stopping the engine. Sometimes, insufficient
vacuum is produced to pull the shutoff switch back into position to stop the
fuel flow. This can be caused by a vacuum leak, a failing vacuum pump or a
failing shutoff switch. When this happens the engine runs at a slow speed
until eventually stopping.
To check some problems, you should have a MityMite Hand Operated Vacuum Tool
(about $30 at Walmart) - which allows you to provide vacuum to different
places to see how they act. Depending on how they act you can determine if
they are getting proper vacuum. Sometimes, the vacuum lines going to and
from the ign switch fail with age - sometimes the vacuum portion of the ign
sw fails - often the shutoff switch on the IP fails - this can be checked by
starting the engine and applying vacum to the switch - if the engine stops
the switch is good - if not the switch is bad.
Changing the switch (~$60 from Rusty) is not difficult - but much caution
must be used to prevent installing it incorrectly - it can cause the engine
to run at max speed until it seizes - turning the key off will not stop it -
only disconnecting the fuel or stopping air flow will stop it - until it
seizes of course. Not pleasant.
That will hopefully get you started - good luck - let us know how it goes -
Larry T (67 MGB, 74 911, 78 240D, 91 300D)
www.youroil.net for Oil Analysis and Weber Parts
Test Results http://members.rennlist.com/oil
PORSCHE POSTERS! youroil.net
Weber Carb Info http://members.rennlist.com/webercarbs
Porsche Road Test http://members.rennlist.com/roadtest/
.
----- Original Message -----
From: "Euan" <[EMAIL PROTECTED]>
To: <mercedes@okiebenz.com>
Sent: Thursday, October 12, 2006 3:13 PM
Subject: [MBZ] 300TD engine shut-off (or not)
Hi there colleague Benzers
My 300TD has started to run on when I switch off. Because this happens
mostly when the engine is cold and grumpy, I'm assuming (based on a
recent thread) that it's a vacuum problem.
I'm completely ignorant of how the pneumatic system shuts the engine
down, so I'd be grateful if anyone knows where to start looking for the
leak.
Thanks
Euan
1985 300TD 5-spd manual
203K mi
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