Should it hold vacuum with ignition on or off. Car won’t shut off. Just replaced shut off valve at pump and tested. Works well. Car does not show vac leaks. Door locks open and close,trans shifts well and brake booster feels ok.

What are you working on, year and model?

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

81 diesel wagon

I would break this down into understandable bits and test in sections. Hook your Mityvac directly to the shut off mechanism you installed on the back side of the injection pump. If it shuts the engine off and holds vacuum, it's OK. Now the part on the ignition switch. Disconnect the brown tube from the injection pump part and the other brown tube from the vacuum source tubing. You now have kind of a loop going under the dash and back out. Turn the key to the run position. Hook your Mityvac the the supply end of the brown tubing. It should hold vacuum. Turn the key to off and you should lose vacuum to the other open end of the brown tubing. Put a cap of some sort on the injection pump end of the brown tubing. With the key still off, pump up your vacuum again. It should hold vacuum. It probably does not. If it did your engine would shut off. Pull off the panel below the steering column and look at where the 2 brown tubes connect to the part on the ignition lock. Look closely at the short rubber tube connectors. They can be a soft oily mess if the diaphragm in the shut off on the injection pump ruptured. The part on the ignition lock can also fail. But it is just held on with two screws. It's not too complicated if you slow down and think it through.

T in your vacuum gauge between the shutoff on the fuel injection pump an that hose you pulled off. Start the engine and let it run a bit and have someone shut off the Ignition and see what vacuum you are getting.

If you are not getting sufficient vacuum to shut off the Engine then it could be the vacuum valve, the position of the hoses if you had the hoses off.

On mine the line going to the vacuum shutoff on the fuel injection pump is brown with a blue stripe. That line goes to the bottom nipple on the vacuum shutoff valve on the steering locum lock.

The solid brown line goes from the top of the the vacuum shutoff valve on the steering locum lock to a Y connector with one leg of the Y going to the main vacuum line and the other leg of the Y going to the vacuum valve on the fuel injection pump that is used on models with automatic transmissions.

When you shut of the the vacuum shutoff valve on the steering locum lock vacuum bleeds out of it; if it held vacuum you would not be able to start the Engine.

__________________
84 300D, 82 Volvo 244Gl Diesel

Post number 8 has a vacuum diagram.

http://www.peachparts.com/shopforum/diesel-discussion/404150-om617-will-not-shut-off-key.html

__________________
84 300D, 82 Volvo 244Gl Diesel

I tested per your instructions and vacuum did not hold. I will get under dash. How best to replace vacuum switch at ignition?

Vacuum pump at new shut off valve on ip did shut off car. So I know that is good.

Pelican has them. Call it a vacuum valve in the search box. It is not expensive. But make sure it's not a simple rubber connector tube. If you look at the catalog picture, you will see the 2 nipples for vacuum and the 2 ears that take the screws into the ignition lock. It's awkward, but doable. I don't think it matters which nipple is in or out. A few months ago I did have a failing vacuum valve that worked in one direction but leaked through in the other. It was trying to shut the engine off as I drove. I reversed the tubes and it worked fine. It took me about a mile to figure that out, though.

It might be tough getting at the 2 screws.

__________________
84 300D, 82 Volvo 244Gl Diesel

It's awkward like anything under the dash. The 2 screws face right horizontally without too much stuff in the way. A short or angled screwdriver and plenty of deep breaths of patience.

Thanks all for the ingo

how in the hell do you even get in there? I can’t even get myself in a position where I can SEE the valve, let alone reach in with a tool to remove it ..do I lie on my back across the seats with my feet out the passenger side, head in the footwell? Seems like torture, at least at my age. But then again, virtually everything that used to be easy is torture nowadays,

On a W123 my guess is you need to pull the instrument cluster out. The instrument cluster is just pushed in but it can also be held in by the speedometer cable which you can pull on to give it slacker and I am not sure on the wiring.

The color coded hoses need to go into the proper position, or it won't work as it should.

You might find the writeups you need below.

DIY Links by Parts Category - PeachParts Mercedes-Benz Forum

When I did mine, I had to swap out the whole steering collum lock as that had pars inside busted up. So that valve came with the new steering collum lock.

Removing the steering collum lock is another way to get at that valve but remember the seat belt buzzer switch is also attached to that.

__________________
84 300D, 82 Volvo 244Gl Diesel