I have a 1992 Mercedes 300SD, W140, which has engine from 1994. When I bought it, the engine didn't shut off when I turned the key off.

I have set everything up via the diagram below. The air from switchover valve follows 1 & 3 (see markings on image). 2 is always closed. When I start the engine, it doesn't start at all because the lever goes down. Per diagram instructions, the 12v should be activated for 3 seconds, but it also looks like 12v is constant which doesn't sound right either. I have tried switching them, giving 12v direclty, but it's not working. Please help sort this out and what the right way to connect is?

Image at link:
https://drive.google.com/open?id=1Osh3u1dTjmTzJXaexLzgA8TqBKazdnD3

With the engine running you turn the key to off and the engine stops?

With the engine off you turn the key to crank and the stop lever goes down?

How do things work if you disconnect the hose in port 2?

With the engine running, disconnect the hoses at ports 2 and 3. Can you blow through port 3 and feel it come out port 2?

Sixto
98 E320s sedan and wagon
02 C320 wagon

A. If I disconnect everything, and keep how it was, the engine will not stop. If I follow diagram, the engine won't start because the stop lever goes down.

A. See first answer

A. There is no air going through at all through port 2

A. When I connect 12v, the 3rd one closes. 2 is always closed, so nothing goes through it.

Do you get 12V across the pins at the switchover valve connector when you turn the key to run/glow and while the engine’s running? Put your finger on the switchover valve and have someone turn the key to run/glow. Do you feel a click? Seems like there isn’t a signal or the switchover valve isn’t responding if vacuum remains available to port 3 during cranking.

For kicks, swap the shutoff switchover valve with the EGR switchover valve. That can cause an EGR fault that makes the ECU cut boost but you only need to test while idling.

If you still have that ‘87 TD, swap instead with the overboost switchover valve between the manifold and the ALDA. Don’t worry about the hose to port 2 if that valve doesn’t have a port 2.

Sixto
98 E320s sedan and wagon
02 C320 wagon

How does the switchover valve function? Does it only give 12 volt for 3 seconds? or is the power constant when car is on? I checked, I get 4.9 volt when testing. When I do 12 volt directly, I do hear the click (closes port 3 - is it supposed to close or open port 2?). I did all the testing as you indicated. I just need to understand the function because I am getting conflicting information per diagram and everywhere I have looked.

AFAIK the switchover valve connects ports 1 and 3 when not energized, 2 and 3 when energized. Key off, shutoff actuator gets engine vacuum. Key on, shutoff actuator isolated from engine vacuum and line vented to purge vacuum (so to speak).

I don’t remember a 3 second signal. The switching valve has no timing circuitry. I’m pretty sure it’s energized the whole time the engine’s running. If it loses power, the engine should stop.

Sounds like you’re not getting a solid 12V signal to the switchover valve with the key on. I wonder if we can borrow a 12V signal from the glow relay. Pin 1 of the small connector should have a solid 12V when the engine’s running.

Then port 2 might be blocked but we can sort that later.

Sixto
98 E320s sedan and wagon
02 C320 wagon

Thank you. Do you have an electrical diagram for the switchover valve?

The switchover valve itself is just a solenoid.

There are SD wiring diagrams in this thread but I don’t see a component legend -

https://www.benzworld.org/forums/w140-s-class/1715881-wiring-harness-1992-diesel-140-300sd.html#/topics/1715881

Sixto
98 E320s sedan and wagon
02 C320 wagon

When I created my 1993 190d 2.2 frankencar I did an electric switchover valve based vacuum shutoff too, worked great the entire 5 years I had the car, still working fine when sold!

For my valve I used an old W126 control valve I had taken off my 420SEL

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

All for the 92 w140 300SD:
functional description : vacuum-engine-stop-with-carkey.pdf
wiring diagram : fuel-cutoff-wiring-1.pdf
testing steps : test-key-operated-stop.png ... not very easy to figure out (for me anyway) and there is a typo "56 seconds" instead of "5-6 seconds"

With the engine idling I pulled the Y9/1 connector and there was zero volts across it. Left it disconnected, turned off the key and saw battery/charging voltage for about eight seconds, then it went back to zero. Engine kept running till I pushed the stop lever down. Pretty much what step 2 in that test procedure said..

Attached Thumbnails

 

Attached Files

	vacuum-engine-stop-with-carkey-ra07206020010x.pdf (109.3 KB, 213 views)
	fuel-cutoff-wiring-1-AEMA158.pdf (108.1 KB, 220 views)

__________________
1992 300SD 140.134 Sold

According to diagram, the positive should go to the N17/3 relay. I discovered that the cable on my car goes to the passenger footwell and into a box. See attached images. What is this box? Also my relay is dated 2011. Could it be the wrong relay?

https://drive.google.com/open?id=1I8f7R7fLZQTWsmL9QDQ9KYSAoX56eXG0

https://drive.google.com/open?id=1LxX5TZv_V8l45P0RnamIj49m_M3AtoQf

https://drive.google.com/open?id=1XX9a60TK-5HoassQIsgiYtcvf7wdhzEX

https://drive.google.com/open?id=1zUaU0sMgyFjoauAaicJDzMc5ksfU1K4N

https://drive.google.com/open?id=1HqGbmJmvckalj0bH6X3sYtEk4HY8Yj0G

https://drive.google.com/open?id=1eMhn39J_CHXP6w9o07VYJA5DzL21Pr1U

I have gotten a membership to AllData, and got the info specifically for this car, but their info is not accurate and very limited. I know you all here are better experts!

When you did the testing, which ports opened/closed for you?

I did find a drawing later (after my post) that showed N17/3's location and it matches the relay in your relay4.jpg picture that you linked to.



When I did that quick test last night I didn't check which port opened. At lunch, I'll walk out and get a picture. I do remember that the "port" towards the front of the engine is connected to the vacuum source (that funny Tee thing on the brake booster vacuum line). And I think the bottom port is connected to the stop valve.

__________________
1992 300SD 140.134 Sold

Thank you all for your help! I have great news. Not only did I figure this out (thanks to your diagrams/attachments), but I also got the RPM gauge and oil pressure gauge to work!! The only thing left to fix is the fuel economy gauge now. I casted 3 birds with one stone, so to speak.

Here is what I found.


Image 1. The 1&2 wires were reversed. Fixed that.

https://drive.google.com/open?id=1IvvIz46wnhK_JAKduTkZomdJysOAZjkM


Image 2. The blue wire from N17/3 was going to left side flywheel housing. Fixed that.

https://drive.google.com/open?id=1wTnpXNeoCb8qoBowmPNOWXy1iN5ZpVOK


Not only were the wires wrong, the hoses going to port 1 & 2 per diagram, are also not accurate. They should be reversed. Ie: vacuum hose goes to port 2.

Here are my remaining questions:

- In images above, I connected wires from group 2 to group 3 and RPM started working. They also work if I reverse them. Does it really matter? (See image with #3 on it)

- Is it better to solder the wires or use special connectors?

I also noticed that the engine started running much better once I got the RPM gauge to work.

__________________
Proud owner of the following Benz over the years:

Current:
- 1992 300SD (W140, OM603) w/engine from 1994

Past:
- 1971 280SE (4-speed manual)
- 1977 300D Sedan
- 1987 300D Sedan
- 1990 300TD (station wagon converted gas to Diesel)
- 1994 CL600 Coupe
- 1998 E320 Station wagon
- 2005 ML500
- 2007 GL450

If the tach wasn’t working then most likely electronic idle control wasn’t working either.

Sixto
98 E320s sedan and wagon
02 C320 wagon