Car is an 81 300 TD. About two weeks ago it quit shutting off with ignition. I found if I held key in door in lock position, it would choke out the engine. I have all four door panels off now trying to find the vacuum leak.

I have narrowed it down to the yellow and 'green' vacuum tube, because if I shut off ignition and crimp any green tube connector the engine will shut off.

Here are my questions. Where do the door vacuum tubes start from? Do they come through the firewall or is there some other starting point inside the cabin.

How can I isolate this leak? I really don't know where to begin tracking down the leak. Thanks
John

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1981 300TD
1985 300TD

Yellow line exiting the firewall to the right of the brake booster. There are diagrams of the vacuum systems on here. You should be able to access all the lines under the floor mats. In the meantime, disconnect that yellow line under the hood and plug the vacuum system so everything else will work apart from the doors and fuel door.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Okay, so here's what I've got. If I plug the yellow and green line under the drivers floor that goes out to the drivers' side door and turn off the ignition, the car stops.
Is this any help as to tracking down my leak? I'm not sure what this means. I have had the door off, nd the vacuum pod does not seem to leak. Any help is appreciated.

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1981 300TD
1985 300TD

Leak is in the door lock system somewhere. Look at the vacuum diagrrams on here and start pulling vacuums on the various open/close lines under the floor mats in the front seats.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

I thought these vehicles had a separate vacuum pump in the trunk for the door locks? I guess yours does not.

Would anyone know if my 1994 S350D has a separate vac pump in the trunk or is there only one main vac pump?

Yours is a totaly different chassis model. the OP has a W123, and does not have a seperate vac pump for the doors. the W123 uses the engine driven vac pump for all the various vac operated systems.
The W124 & W201 have a electric driven vac pump under the rear seat , & the W126 has it in the trunk.
I assume your model has the pump in one of those locations.

MAINCEDES, be good if you have a Mity Vac to chase down the vac leaks.
You will see a yellow plastic pod next to the firewall, this is the vac check valve. there is one line going into it off the large black vac line going to the Brake booster. then 2 yellow lines going into the firewall from the check valve. one line goes to the drivers door, and the other goes to a vac storage tank. the sedans have it over the fuel tank in the trunk. not sure about the TD.

The drivers door is just the master switch to divert vac for lock and unlock for the L/R, R/F & R/R doors and the fuel door and trunk. the storage tank is only for the operation of these doors etc... when the engine is off.

If this part of the system has a leak, then it causes problems with eng shut off and trans shifting.

Lift the carpet on the drivers side, and under a black plastic cover are yellow lines with a red or green stripe, red = lock, and green = unlock side of the system. unplug the lines going to the L/R door, and using the mity-vac, you will be able to see if the door actuator in this door is working, if it is then work your way to the R/F and so on until you locate the leak.

As kerry said, the Vac to the yellow check valve can be unpluged, and then plugging the line to it will cut that part off so the eng will shut off until you locate the problem.

The Mity-Vac is your friend to keep these systems working.

Charlie

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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

Thanks for the help. I have temporarily plugged the door lock line, and engine is shutting off. How nice.
I do need to invest in a mighty vac, but in the meantime, I used my mighty lungs on Sunday and traced the problem to the drivers' door. It seems to be the master switch. Not sure if I will try and replace or just live with the lack of door locks. I never lock anyway.

I have one more question. While I was messing around with everything, starting the car quite a few times to try and find the source of the leak, I found that the shutoff switch under the hood would not shut the car dow. It would start to choke, and then just knock pretty bad but keep running. Is this a bad sign??

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1981 300TD
1985 300TD

Yellow w/ green stripe is the unlock line. Before disabling or completely isolating it, I'd make sure the trunk was in the manual position so you're not stuck. Likewise with the fuel flap.

You may have a leak in one of the other locations, since the master switch distributes vacuum; IN to the switch via yellow, OUT via yellow/green and yellow/red