Do the hose positions matter on the ignition switch vacuum valve, or are they interchangeable?

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1981 Mercedes 300TD, 1994 Honda Civic Del Sol
http://mefi.us/images/fuelly/smallsig-us/67195.pnghttp://mefi.us/images/fuelly/smallsig-us/103885.png

The all colored Brow Vac Line comes out of the Top.

The Brown line with a Blue Stripe comes out of the side of the Valve.

I have not read anything on any of the Forums that has said what happens if the Vac Lines are incorrectly installed.

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84 300D, 82 Volvo 244Gl Diesel

I think that they are position sensitive as the valve is open in the stop position, and in run it vents the shutoff valve.

__________________

Gone to the dark side

- Jeff

Yes. There was a thread on this recently. A forum member switched vacuum lines and it didn't work.

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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

yep, if you reverse those lines you're car wont shutoff properly (assuming w123/om617/616).

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1982 240 D, 308,000 - 321,127 miles (sold)
1982 300 TD,166,500 - 226,000 miles
1998 E 320, 120,000 - 144,000 miles
2005 C 230 K, 26,000 - 77,000 miles (sold)

Thanks guys. I'll check it out. I've been hunting down an intermittent shutdown problem, the kind where it's right on the edge and sometimes doesn't quite manage to stall the engine. I've fixed several vacuum leaks already, and will make sure the switch is connected properly.

Am I right in thinking with the switch ON it should hold vacuum on one side and not on the other?

__________________
1981 Mercedes 300TD, 1994 Honda Civic Del Sol
http://mefi.us/images/fuelly/smallsig-us/67195.pnghttp://mefi.us/images/fuelly/smallsig-us/103885.png

The brown line is sourced from the main vac line, the brown/violet line goes to the shut off actuator.

Pic courtesy wHunter.

Attached Thumbnails

 

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83 SD

84 CD

Before I started tearing into that switch, I'd put a Mity Vac inline with the shut off valve and monitor the vacuum level when shutting off to get a numerical sense of what is happening. It's pretty rare for those switches to fail. More likely a vacuum leak somewhere else in the system, maybe even in the shut off valve itself.

__________________
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

I've done some checking with my MityVac. The shut-off valve holds vacuum, so it would appear to be OK. The underhood hose from the shut-off valve to the switch holds vacuum with the switch in the ON position. The underhood hose from the vacuum system to the switch will pump up to a few inches Hg with the MityVac but will quickly leak anything above that. With the shutoff valve connected and the switch OFF, the MityVac shows the same kind of fast leakage. So I'm thinking probably I have a bad hose connection under the dash, unless the switch itself is leaky.

My theory is it's so intermittent because it gets in a race between the leakage and the declining output of the vacuum pump as the engine slows down. Sometimes it shuts off, other times the RPMs drop, then oscillate back and forth before settling to a low idle.

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1981 Mercedes 300TD, 1994 Honda Civic Del Sol
http://mefi.us/images/fuelly/smallsig-us/67195.pnghttp://mefi.us/images/fuelly/smallsig-us/103885.png

Sounds like the switch is plumbed backward.]

With the switch off, you should be able to hold vacuum in either direction through the valve with the other line plugged (switch/valve is connecting the two lines). Pulling vacuum at the brown line (to vacuum pump) should pull down the shutoff valve and it should stay down/vacuum maintains.

With the switch on, the brown with tracer to the shutoff valve should hold no vacuum as the switch/valve should vent the vacuum allowing the shutoff lever to rise. From the solid brown hose (source/vacuum pump one) to the switch/valve it should hold vacuum.

Hope this clears it up.

__________________

Gone to the dark side

- Jeff

All right, never mind. I was clearly loopy when I did those tests. (It was at the end of a long day of wrenching; I probably either remembered wrong or got my connections confused.) I tested again today and the shutoff valve is clearly not holding vacuum. #$@$*! I was hoping to not have to mess with that part because it scares the crap out of me.

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1981 Mercedes 300TD, 1994 Honda Civic Del Sol
http://mefi.us/images/fuelly/smallsig-us/67195.pnghttp://mefi.us/images/fuelly/smallsig-us/103885.png

Swapping that out is easy, just pay attention to the orientation of the old one when you take it out.

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83 SD

84 CD

Just have heard way too many stories of runaways from that procedure to be entirely confident in it.

I have heard that if you put vacuum on the new one with a MityVac before bolting it in place, and it holds itself in position, it's engaged correctly. Any truth to that?

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1981 Mercedes 300TD, 1994 Honda Civic Del Sol
http://mefi.us/images/fuelly/smallsig-us/67195.pnghttp://mefi.us/images/fuelly/smallsig-us/103885.png