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Old 09-11-2010, 07:11 PM
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Join Date: Jun 2010
Posts: 6
diy vacuum switch?? 240d

Hey guys, I just got a 1975 240d and it came with an engine/trans out of a 1981 240d. I can get it started but I can't get it to stop as the ignition sequences are different from both models. Any ideas about what I should do??

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Old 09-11-2010, 07:38 PM
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Join Date: Jan 2002
Posts: 18,355
Get a piece of rubber vacuum hose and hook it to the shut off valve on the back of the IP down between the IP and oil filter housing. Run the other end thru the firewall into the passenger compartment. When you want to shut it off, suck on the vacuum hose. Typically takes 2-3 good sucks. Simple. Reliable. Sexy.
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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Old 09-11-2010, 08:24 PM
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smoke gets in your eyes
Join Date: Jun 2000
Location: SF Bay Area
Posts: 20,801
Someone converted a W123 240D to electric engine shutoff rather than mess with a faulty key switch. It's a matter of finding a VSV that blocks airflow when energized. The overboost VSV from any 80s MB turbodiesel should work. When energized, the VSV plugs one end and vents the other.

Assuming you have a vacuum source in the engine bay, hook up the VSV between the vacuum source and shut-off actuator on the 81 240D IP with the plugged port to the source and the vented port to the shut-off actuator. Wire the VSV so it's energized when the key is in the RUN position. When you turn the key to RUN, the VSV plugs the vacuum source and vents the shut-off actuator line. When you turn the key to OFF, the VSV connects the vacuum source to the shut-off actuator to stop the engine.

I don't remember who came up with this so I don't know his experience with the longevity of an overboost VSV used this way.

87 300D
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Old 09-11-2010, 11:11 PM
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Join Date: Jun 2010
Posts: 6
awesome guys! This is my first diesel but not my first merc, I think im going to like it here!

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