Could bad shutoff keep engine from starting?
 

Well, this sucks. Couldn't get the SD started this morning, it's been getting progressively worse over a few days, have GP's on order even though only one tests bad with the meter, but the this morning it just won't start. Run it through a few GP cycles, can hear the relay clicking off, no go, double check the fuse, rebleed it for grins while it's jumped to another car recharging, no go, start to wonder if something happened to the compression, for the hell of it I pull the brown shutoff vac line out of the main vac line, and it starts!

Check under the dash, and sure enough there's oil at the switch, so looks like
I'll be replacing the shutoff, but has anybody heard of it failing in a way that keeps it from starting? Went to the ******** site, is it also called a shutoff solenoid or am I looking at the wrong part?

While doing searches I see a number of people talking about oil coming from failing vac pump, but I'm confused how oil could be going out the line against the incoming air that's pumping into that thing?

To top it off while opening the hood to use the shutoff lever I break the stinkin' lever off! For now if I wedge it just right it'll pull the cable, but sure didn't need that on top of the other problems :mad:

If there is oil in the dash coming from the vac line to the ignition switch I think there's some very bad vacuum pump problems going on! :eek: I assume that probably caused a clog or problem with the shutoff valve as well, preventing it from starting. Do you have hard brakes or other signs of a failing vacuum pump???

O.K. answered some of my own questions, yes it is sometimes called a shutoff solenoid, yes a few people have had starting problems related to the valve.

oil at ignition switch
 

This is gonna sound crazy,but I had an '84 SD that pulled oil up to the Ign.Sw.
and from there to the A.C. controller.
'cleaned everything up as best I could and replaced the vacuum shutoff on the
back side of the Injection Pump.(put a Primary/clear/V.W. fuel filter in the
line between the ign.sw. and the I.P. shutoff to give me some advanced
warning in the future.)

Vacumm is a wonnerful thing, BUT eventually everything ends up at the PUMP.

To answer your original question: The vacuum shutoff's default (without
vaccuum applied) [or a "BAD" shutoff] position is only waiting for the starter
to apply R.P.M.s after the Glow Cycle...COMPRESSION BASED IGNITION!

I can guarantee you that you can have a good vacuum pump and oil under your dash, when your IP shutoff valve dies. Ask me how I know.
You can put a mityvac on that line going to it and find out easy enough.
Those things are $40, read the warnings about run-away engines prior to doing the job so you do it right.
I did a whole thread about this, lots of info here.
My guess is the shutoff valve is toast.

The vac stuff seems normal, no hard brakes, can hear actuators going in response to A.C. settings, pretty sure it's the shutoff. But still confused as to some of the search results where there are concerns about oil coming up the line from the pump, I can see how it would go from the I.P. to the pump, but the other way? Guess I'll be getting a Mityvac, the guy I used to borrow one from at work quit....

When you shut the car off, the pump is done creating vacuum. But there is still vacuum in the system (via checkvalves), that's how your locks still work for awile, ect. This vacuum sucks oil right up to the ignition switch, that's where it goes next if the shutoff valve is leaking oil. First-hand experience here.
I cleaned out the lines with brake cleaner, worked great. Make sure they are dry before reassembling. I also replaced the rubber connectors which had gotten quite soft in several places.
Ensure the shutoff valve goes in correctly (potential run-away engine!!!!!!!) if you find that to be the source of your issue.
Check the top of your radio for oil!

Well that's one less worry, no radio yet! The p.o. took his out when I bought it. And for Jimmy Joe,not that it matters but the locks on an SD work off of a pump in the trunk not residual vacuum, but thanks for the other tips :)

Soy,

Locks only work off the electric vacuum pupmp in the trunk for '81 and newer MB.


P E H

Jimmy Joe,

I always wondered how oil got into the vacuum system from a bad vacuum pump. I could understand how oil would flow toward the vacuum pump from a bad IP shut off valve, but not flow away from the v-pump. You answered my wonderment. Thanks.

P E H

Thank you PEH,
it feels good to add something of value, especially when appreciated by one of the great minds, like yours, here. :)

Jimmy Joe,

Thanks again.

P E H

For P E H, you can just call me Matt, plus, I have an '82 SD right now....funny aftermath to this, hooked it up temporarily with a short vac line coming off the keyswitch with a rubber connecter on it long enough to stick out under the dash to hook to the line going to the shut off so I can hook it up for long enough to shut off the engine, but not too long, until I get the new part, then stopped to talk to a friend in the parking lot, shut off the key but didn't hook the lines up, didn't talk long enough to make it worth shutting down, then proceeded to back out with the steering wheel locked! It's a weird feeling when that wheel won't turn but you're moving....

Matt,

On the older 190D,220D and 240D with the "Gorilla Knob" for start, GP, shut off and run, you could push the knob in and turn off the key and then pullout the knob and the engine would run with the key off even though the electrical system was shut off. It would also run with the key out of the switch but the steering wheel would lock.

P E H

Yeah, I miss my knob from my 240 D, reminded me of starting a boat, and loved the simplicity of seeing the little glow through the holes, who needs a relay.... :rolleyes: