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  #1  
Old 10-19-2018, 07:59 PM
Ten13
 
Join Date: Apr 2017
Location: Orinda, CA (SF Bay Area)
Posts: 93
Part Identification help: '74 W114 vacuum switch?

Hi there,

I'm working to diagnose stone-cold start issues in my newly-acquired '74 280 Sedan with the following engine code: 110.921.12.028948. This is a California car.

The small canister, which I assume to be a vacuum switch, possibly called the "idle vacuum valve", (seen in attached photos with the little red painted cap on the top) makes a loud buzzing sound after the engine has been warming up for about 30-45 seconds. You can actually feel it vibrating with your finger. Wait another 2 or so minutes, and the idle starts to fluctuate about 50-100 RPM for another minute, as the engine continues to warm (in response to the buzzing sound now fluctuating, from the vacuum switch). Eventually, it stops buzzing and the idle is steady.

I can't see a part number anywhere on this device, only the "A. Peirburg A.G." stamping (as seen in the 2nd photo).

Is this a serviceable part? It appears to be adjustable.

If not, any idea what the part number might be? The closest thing I've found is this:

https://www.ebay.com/p/MERCEDES-BENZ-W-116-W-114-280-450-300-Fuel-Pump-Valve-Pierburg-M-115-M-110-M-117/1523299479?iid=323469440600&chn=ps

It's obvious to me that this is controlling the timing, because when the idle is fluctuating, there is no movement of any part on the carburetor. When warmed up, there appears to be no function at all.

Thoughts?

Thanks in advance!
-greg
Attached Thumbnails
Part Identification help: '74 W114 vacuum switch?-img_8899.jpg   Part Identification help: '74 W114 vacuum switch?-part-1-cu.jpg  
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Filmmaker, Dad, Citizen of the World in the San Francisco Bay Area
=== current vintage stable ===
'74 280 sedan '78 280CE '92 500SL '73 VW Thing
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  #2  
Old 10-20-2018, 10:31 AM
meltedpanda's Avatar
Certified Benzaholic
 
Join Date: Mar 2003
Location: Central Ky
Posts: 6,116
it is a purge valve of sorts . IIRC it helps close air intake at some port on the carb and then opens when warm. Have you traced the vacuum lines attached ? There may be a part number on the back side of the attachment. I have several of these lying about , I will take a look at them to see if they are the same
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2011 Porsche Cayman - Bond,James Bond
99 E320 THE Queen Mary
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72 450SL, Pearl-SOLD
16 F350 6.7 Diesel -THOR
07 Lexus RX 350 - Lexi
14 38HP John Deere 3038E Tractor -Mean Green
84 300SD, Benjamin -SOLD
71 220 - W115-Libby ( my first love) -SOLD
73 280 - W114 "Organspende" Rest in Peace
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  #3  
Old 10-20-2018, 06:00 PM
meltedpanda's Avatar
Certified Benzaholic
 
Join Date: Mar 2003
Location: Central Ky
Posts: 6,116
I have a few of these , all have the same markings and no part numbers, one of them has the name and KG after it. , I dont really know how to test them , but they came off a working car back in the day. You are welcome to them , postage and a cup of coffee
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Ron
2011 Porsche Cayman - Bond,James Bond
99 E320 THE Queen Mary
62 220b - Dolly - Finally my Finny!
72 450SL, Pearl-SOLD
16 F350 6.7 Diesel -THOR
07 Lexus RX 350 - Lexi
14 38HP John Deere 3038E Tractor -Mean Green
84 300SD, Benjamin -SOLD
71 220 - W115-Libby ( my first love) -SOLD
73 280 - W114 "Organspende" Rest in Peace
81 380 SL - Rest in Peace
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  #4  
Old 10-25-2018, 03:54 PM
Ten13
 
Join Date: Apr 2017
Location: Orinda, CA (SF Bay Area)
Posts: 93
Quote:
Originally Posted by meltedpanda View Post
I have a few of these , all have the same markings and no part numbers, one of them has the name and KG after it. , I dont really know how to test them , but they came off a working car back in the day. You are welcome to them , postage and a cup of coffee
Hey there - that would be swell. Mine have no part #'s, upon closer inspection. If you're still open to your offer, I'd love to receive them. I'll reach out via private message and of course, I'm happy to pay you for shipping plus enough for a good cup of coffee or five. I'm in California, so getting together at a cafe might be a logistical challenge!
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Filmmaker, Dad, Citizen of the World in the San Francisco Bay Area
=== current vintage stable ===
'74 280 sedan '78 280CE '92 500SL '73 VW Thing
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  #5  
Old 10-28-2018, 07:31 PM
Registered User
 
Join Date: Oct 2012
Posts: 10,670
There are usually three of these per car depending on the options, years, etc.

This is known as a switch over valve. After that they have specific names. This one sounds like an ignition retard valve. It regulates your timing and changes it when the A/C is switched on.

The operation and repair of these valves is far beyond what I could write here. Replacing with a known good ones is usually the cheapest way to go. While it is nice to understand their operation this is an item that rarely needs attention and there is a lot to learn about them.

If you are looking for further info search for switch over valves. During the 70's Mercedes used them everywhere. Pull the center console out of a 116 with auto temp control and you will find a lot of these hiding back there, all of them designed to do a specific task.
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