W123 300D won't shut off--vacuum leak? HELP! - PeachParts Mercedes-Benz Forum

herring · #1 12-12-2007, 01:25 PM

Ok, thanks. I am feeling much better about this. I'm not much of a mechanic but can follow directions and part of the reason I am interested in a W123 is the famed ease of working on them. So long as I've got another car to get to work in in case I screw up I'm not afraid to dig in.

Question: While I'm working on the vacuum system is there any chance of putting the car into a runaway state as discussed here (skip halfway down the page to get to the Mercedes part

http://www.motorwatch.com/automotivebible/mechanics_nightmares/mnmDiesel.htm

Quote:

You're probably wondering why MBZ diesels run away. First, they rarely throw off their flywheels and seldom explode. But, it can happen in one of two ways. The first is when the throttle linkage sticks. This isn't much of a problem as long as you keep the ball-sockets properly lubricated. MBZ fits the engine with a shut-down lever that looks like a choke knob. Also, located right above the injection pump, is a manual fuel cut-off device. But, modem MBZ diesel engines use a shutdown system that's operated by the ignition key. A small vacuum motor mounted on the rear of the injection pump performs the shut down.

The second way is when the vacuum motor diaphragm ruptures. The owner find that the only way to shut down the engine is to get out, open the hood, and press the manual shut down lever. Not the sort of thing that MBZ owners could be likely to do, huh? Well, the replacement of the vacuum motor can be tricky. It has a small tang on it that must catch in a notch on the injection pump rack. If it doesn't, it'll jamb the rack in a wide-open-throttle position and bingo, "Runaway Diesel."

kerry · #2 12-12-2007, 01:37 PM

Yes, replacing a vacuum shut off diaphragm incorrectly can cause the engine to runaway. It is a simple problem to avoid. All you need is a readily available method of stopping the engine should you make the mistake.

Jordan G · #3 12-12-2007, 01:42 PM

Quote:

Originally Posted by herring

Ok, thanks. I am feeling much better about this. I'm not much of a mechanic but can follow directions and part of the reason I am interested in a W123 is the famed ease of working on them. So long as I've got another car to get to work in in case I screw up I'm not afraid to dig in.

seriously, you've come to right place.....as for having another car in case something goes wrong? Well, I can't help you there....for I'm but a foolish boy.

bad morning

See post 32

nate300d · #4 12-12-2007, 01:57 PM

My three experiences were always door lock actuators. A quick way to test this is to start the car shut it off (assuming that it will not) and then lock the doors. If it then shuts off (slowly) then you likey have a bad door lock line or actuator.