W123 diesel run-on - PeachParts Mercedes-Benz Forum

The Swede · #1 08-20-2007, 03:34 PM

When the car is shut off, most of the time she'll run on. I hooked up a Mity Vac to the fuel shut off valve, barely 2 pumps and she shuts down.

A Russian mechanic I know (used to work on the oldies back in Mother Russia) told me in broken English that there's something vacuum related in the ignition switch (??)

My guess was a vac leak somewhere else. All the line, splitters etc. look good in the engine compartment. So it's a matter of testing each branch, etc. PIA!!

Johnhef · #2 08-20-2007, 03:47 PM

plug off the green (climate) vac line and the yellow (locks) ones. although now that I think of it, you said yours is a 79(?) I'm not too familiar with how the vac system works for climate unit on cars with the big servo.

anyways with those lines plugged, try to shut off the car and see what you get, if it works, try adding one then the other back in to see if you can isolate which system(s) has the leak.

if it doesnt work, with the engine running, plug the line to the shutoff valve directly into the main line and it should cut off almost immediatly. if not, you may have a weak vacuum pump.

John Schroader · #3 08-20-2007, 03:48 PM

I'm pretty sure that the problem could well be vacuum related. Mine would sometimes fail to shut down. Could shut it off with the kill switch next to the IP. As time went by, I learned that I could rev up the engine (therefore increasing the vacuum) and it might shut down. Finally even that wouldn't work. I replaced the vacuum shutoff solenoid (this is probably not the proper name for it) and it works great. Learned how to do that on this forum. If I am correct, when the ignition switch is on, the vacuum pump draws a vacuum through (among other thing) the ignition switch. When you turn the switch off, the vacuum is routed through the switch to another line to the vacuum shutoff solenoid. If there are lots of leaks, or the ignition switch is bad, or if the shutoff soldnoid is bad, then the engine will not shut off. If a couple of pumps with a mighty vac will do the trick, then I would guess that the shutoff solenoid is good and the problem lies in one of the other areas. I surely am a weak link in the advice area, but I think I have a clue on this one.

mistergood · #4 08-20-2007, 03:50 PM

Someone correct me if I'm wrong... There def is vacuum that runs from the ignition switch, which will feed that vacuum through to the shut off valve when the ignition is cut off. The vac line in the engine compartment is brown (at least on mine it is). If there is a bad connection there... or no connection at all then the car will remain running until you shut it off manually. If this line is connected and it all looks ok in the engine compartment, one way to try to shut your car down is to try locking the doors after you turn the ignition off. This will pretty much always shut mine down if she is slow to do so with just the ignition. And if that works *fingers crossed* then you have limted the vac leak to somewhere inside the car! Maybe under the dash, maybe under the carpet, maybe in the trunk! Time and a mityvac will tell. Good luck. Hope this helps at all.

SwampYankee · #5 08-20-2007, 03:57 PM

Quote:

Originally Posted by The Swede

When the car is shut off, most of the time she'll run on. I hooked up a Mity Vac to the fuel shut off valve, barely 2 pumps and she shuts down.

A Russian mechanic I know (used to work on the oldies back in Mother Russia) told me in broken English that there's something vacuum related in the ignition switch (??)

My guess was a vac leak somewhere else. All the line, splitters etc. look good in the engine compartment. So it's a matter of testing each branch, etc. PIA!!

Definitely vacuum related since you mentioned the lock/unlock issue after sitting. Take the PO up on his offer to check out that rear door. Since he mentioned it, that's probably a good place to start. Bring him a beer, put him to work!

The Swede · #6 08-20-2007, 04:48 PM

Thanks for the replys.

I'm sure it's not the fuel shut off valve, since I shut that off with 1.5 squeezes from the Mity Vac. And yes, it's the brown line that connects to the valve.

Rubber lines/connectors look good in engine comp't, so I guess it's time to start isolating all the vacuum circuits with a Mity Vac as Johnhef wrote. A good project to do outside in in the sun. It's been raining here the last few days, so hopefully next weekend will be nice.

Also as I mentioned, the rear pass door lock doesn't always actuate (all the others do) so there's something awry, PO had issues with it.

This is a good resource, if/when vacuum issues arise (Nice write-up by Andrew)
http://www.schumanautomotive.com/forums/showthread.php?t=2755

The Swede · #7 08-20-2007, 06:57 PM

After futzing under the hood this morning, the car is shutting off as normal. Weird.

Also, a product note. I ran a bottle of Sea Foam in a 1/4 tank.

Previously, the car smoked (not a lot) at start and under throttle. No longer. I just filled her up w/o any additive, so I'll see how it goes. I've read that Redline's Diesel Catalyst works well, but Sea Foam seemed to do the trick.

JimmyL · #8 08-20-2007, 07:16 PM

Quote:

Originally Posted by The Swede

After futzing under the hood this morning, the car is shutting off as normal. Weird.

I'm with John. I don't know a whole lot about the vac system on cars with the Evil Servo, but I know on my wagon when my climate control is set a certain way it won't shut off. I think it is when I have the temp dial set to heat. Also I had an issue with a door lock vac pod, and when i turned the key off, I could lock the doors and the car would shut down.
So, you might try different climate control settings while turning off the car. {never mind if it is always on the same setting and you haven't changed it}

You've had very good advice above, and from the old Russian.....

Dieseldoofus · #9 08-20-2007, 07:59 PM

Jimmy-

That reminds me of a guy I read about having to hit the defrost button for his 126 to shift smoothly.

The Swede · #10 08-20-2007, 08:04 PM

Locking the doors won't shut it off, not sure about the HVAC, kinda doubt it. That's been re-done.

The cruise control is disconnected, so if you put your finger over the nipple on the vacuum pump, she'll shut down.