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Mercedes 300D
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Discussion Starter #1
Hi, I have an '81 300D with a vacuum problem. The previous owner told me that he thought that one of the hoses/diaphragms in the passenger side was leaking, didn't want to deal with it and had someone just disconnect the hoses for the locks and cruise. I never bothered to check it out before. But, I finally decided that I'd tackle it. I went under the hood and found that a screw had been placed into one of the vacuum hoses that leads from the (I think) cruise control actuator mounted on the fender well. There is also a 3-way vacuum fitting that had been just left dangling and not connected to anything but hoses that go into the firewall. I connected the 3-way to the hose that had the screw in it and voila the door locks worked...sort of. They lose pressure when the car is not on. But, since connecting those hoses, the car will not turn off. I have to turn the car off with the STOP lever in the engine compartment. I didn't see any other hoses that weren't already connected to anything. So, I assumed that this was where the connection was broken.

Should there be a problem turning the car off with these hoses connected? I can deal without locks, but I don't think that I want to deal with manually turning the engine off under the hood. If this condition is due to a vacuum leak in the doors somewhere, I can look into fixing that later. Thanks for any insight!!
 

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BenzWorld W126 & W201 Host
1988 420SE, 2002 C180 Kompressor, 200 ML320
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Vacuum leak

Joey

The engine uses vacuum to shut off. Your system has a leak and as such it can't build up the pressure required to shut off.

You need to try and trace where the leak is, it's usually one of the door locking valves.

If you pull the carpet up in each foot well, you should be able to see where the vacuum pipe goes up towards each door. Find where the each door supply joins the main line, disconnect them and blank them off one at a time and you should be able to establish which door is causing the problem. ( golf T's are ideal for blocking the pipe).
 

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re: Vacuum leak

Thanks! I checked the archive first, but didn't see anything connecting the engine shutoff to the door locks. In any event, this helps tremendously and thanks for the tip.
 
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