Shutoff valve test clarification for 78 240d - PeachParts Mercedes-Benz Forum

BodhiBenz1987 · #1 05-13-2012, 11:13 PM

I was trying to remove the glow plugs for an eventual compression test, and in the process noticed a crack/hole in the rubber bit holding the vaccuum line to the shutoff valve. Since I had the line off to replace it anyway, and was curious, I tried hooking the MityVac to the shutoff valve and applying vaccuum (with engine off). I noticed two things 1) It does not hold vaccuum ... it holds for a couple seconds than drops down and 2) the stop lever doesn't move at all. The car has been shutting off pretty normally as I can tell, so I'm assuming if I applied vaccuum with it running it would still shut down. Are my observations with the engine off an indication the valve may be in the process of failing, or are they normal? I've read a lot of posts saying vaccuum applied to that nipple should move the stop lever down, but I was thinking that might be in reference to the later IPs? Mine has the kind of lever attached to the external throttle linkage as opposed to side of the IP.
So, should I just plug it back in (with new rubber connector obviously) and not worry about it as long as it shuts down easily, or is it a problem waiting to happen? Anything that has to do with the shutout valve freaks me out a bit, because of all the runaway threads I've read.

kerry · #2 05-13-2012, 11:19 PM

As long as you're not sucking oil up into the mityvac and it shuts down, I wouldn't worry about it. Start up the engine, pull a vacuum on it and make sure it shuts off.

Phillytwotank · #3 05-13-2012, 11:25 PM

It's in process of failing. It can still shut down even if it has a small leak. It will get worse and will eventually be unable to hold enough vac pressure to shut the engine off... Could be sooner or later. No telling for sure but, as long as the mechanical throttle linkage is well adjusted, you will always be able to stop the engine with te stop leaver. It's super easy to replace but the replacement part is getting pretty expensive.

The stop leaver is not directly connected to the shut off valve so you won't see any movement when vac is applied to the valve.

charmalu · #4 05-14-2012, 01:37 AM

If you do need to change the shut off valve, here is another approach to making sure you connect it correctly.

http://www.peachparts.com/shopforum/2931575-post20.html

Charlie

JamesDean · #5 05-14-2012, 02:12 AM

Quote:

Originally Posted by Phillytwotank

It's in process of failing. It can still shut down even if it has a small leak. It will get worse and will eventually be unable to hold enough vac pressure to shut the engine off... Could be sooner or later. No telling for sure but, as long as the mechanical throttle linkage is well adjusted, you will always be able to stop the engine with te stop leaver. It's super easy to replace but the replacement part is getting pretty expensive.

The stop leaver is not directly connected to the shut off valve so you won't see any movement when vac is applied to the valve.

Agreed. My one 300SD would take a second or two to shut down after the key was removed. Turns out the shutdown valve was going south, it had a leak in it.

In my case, the stop-level on the linkage has been rendered useless due to some "repairs" I had to enact. So having a bad shutdown valve was a no-go.