I located a vacuum leak in my '85 300dt. The leak is on the clear / fuchsia line input of the part shown in the attachment. What is this part called? What does it do? It is on the driver's side firewall though the same part is near the SLS resevoir on the passenger side in my '84 300tdt.

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1985 MBZ 300DT
1969 MBZ 220d
1984 MBZ 300TDT
1981 VW Vanagon

Are you sure its in the firewall? Looks like its in the wheel well. Mine was. Blue/purple/white line goes to the ARV. Blue/white goes to the vacuum supply. The part is called vacuum converter switchover valve in my diagram. Open/closing is controlled by the EGR contol unit.

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'85 300D Cal 280,000 miles
'14 GLK 350 60000 miles

Sorry... you're correct. It is on the wheel well.

If my EGR and ARV are disabled (for offroad of course) then fixing this would be unneccessary, correct? Can I just plug the vacuum source hose?

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1985 MBZ 300DT
1969 MBZ 220d
1984 MBZ 300TDT
1981 VW Vanagon

I would plug it in the vacuum source and in the parts(ARV, EGR) plus remove the electrical connectors. If you want, you can remove the converter and switchover valve altogether for off road use.

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'85 300D Cal 280,000 miles
'14 GLK 350 60000 miles

So... in the attached vacuum diagram, which hoses would you recommend plugging? There are two hoses near the 'vent filter' off the injection pump that I'm not sure about.

Also, can anyone explain what the purpose of the 'positive vent line' to the passenger compartment is? What is this line connected to?

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1985 MBZ 300DT
1969 MBZ 220d
1984 MBZ 300TDT
1981 VW Vanagon

Califorinia or federal? What color is it? CD-ROM from MBUSA, no info. With a helper try to locate under dash. I'm thinking, at least I've heard, goes nowhere.

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83 SD

84 CD

Why not just get new hard plastic line to replace that and cut to length? I think MB still sells them. Just give them a sample or take the leaking hose with you.

The 85 is quite more complicated with the additional vacuum lines. It looks like that's right beside the kilma relay? Looks like unplugging/blocking it may also affect shut down, as one line also goes to the IP area near the shut off valve.

Positive vent line is just an open line to vent into the clean cabin air. Nothing connected to it from there.

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http://farm8.staticflickr.com/7271/7...144c3fc1dc.jpg

The leak isn't really in the vacuum line... I didn't really clarify this in my orginal post. It is in the valve itself. Hence, I'd prefer to just disable this valve since the EGR is already disabled.

The car had an '85 style vacuum system as shown in the attachment in my previous message. I'm still not sure what the two lines near the vent filter are for. Is the 'positive vent line' not pulling vacuum? I.e., is it actually positive pressure? I'm assuming the two lines in question would do the same. If these lines are only necessary for EGR/ARV I'd prefer to plug them to 'simplify' the vacuum system (as I'm currently experiencing vacuum problems).

I am having shutdown issues. The car takes a few seconds to shut down after turning the key to the off position. I have tested the shutdown valve and it works fine. Looks like I'll be playing with the mighty vac this weekend...

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1985 MBZ 300DT
1969 MBZ 220d
1984 MBZ 300TDT
1981 VW Vanagon