OnTheCase

I have an 84 300 turbo Diesel. When I turn the ignition off and remove the key,the engine stays running and I must open the hood and press the "stop" button to kill the engine. HELP

sosh

The electric fuel cut off solinoid is not working, Your dealer can fix this easily

OnTheCase

Why can't I fix it myself? is it a matter of a part swap out. Could the solenoid be stuck or not be getting proper voltage?
I just had a cut off solenoid problem on my toyota. Holly left the o-ring off of the tip of the solenoid. thx, Lee

sosh

You can fix it yourself if you are prepared to troubleshoot the wiring, switch, solinoid and fuse/relays and have the proper equipment/tools to do so. You must also be prepared to purge all air from the fuel system if necessary.

mbtech208

Mercedes diesel engines have a key switch controlled/vacuum actuated shut-down system. A vacuum actuator on the injection pump is connected to the control rack by a linkage. When the key is turned to "off", a cam in the key switch actuates a valve and vacuum is applied to the vacuum unit. This pulls the control rack to the "stop" position, shutting down the engine. My guess is either you have a bad key switch, leaky vacuum control unit on the injection pump, or a bad vacuum pump itself.

lowvolt

I'm having similar problems in my daughter's 78 300D. Related symptoms are:

Fuel cutoff solenoid appears to not be energizing, which keeps the engine from starting.

Solenoid sticking, may be just the solenoid, but maybe the key switch itself.

Glow plug light not coming on as switch is engaged, but only as switch is beginning to be disengaged.

It really feels like a bad switch, and also seems to be related to steering wheel posiiton.

Is it difficult to replace the key switches on these 25 year old models? I'm a pretty good sized guy, and it's hard to fit under the dash to work on most smaller cars. Must it be a factory key switch, or can the cutoff functions be put on separate switches?

This seems to fit in with the thread, so I didn't start another.

flippurr

I would agree with Dave's post but want to add some more possibilities before you go buying new stuff. On the drivers side in the engine compartment, near where a bunch a wires come through the firewall from the cab there are some vacuum lines that meet and tee off to several places. Look for any of these to be unplugged, one of which goes to the ing. switch and when in the off position shut down the engine. Do your door locks work? If not then look in the same spot for that vacuum line too! In some models like mine 83 300d there one in the same, if the line is undone, I have no door locks and no shut down. This woudl be a good place to start. Another way to check if the shut off diaphram is good is to put a good external source off vacuum to the ing. switch and turn off the switch to see if it stops the engine because it should. As long as you get the right one still left on the ing. try both if you are not sure.

flippurr

sph17

You have been given very good informtyion all ready. I want to stongly suggest you check for a vacuum leak first. If this happened suddenly, especially if you just changed your oil, most likely it is a vacuum leak as discribed in the previous post by where the vacuum tubes and electrical wires go though the firewall. In changing the oil it is very easy to pull one of the vacuum lines from the plastic connectors. Some silicone cement on the plastic tube helps seal the connections.

Other places for problems are the hard plastic tube that runs from the front of the engine (from the vacuum pump) to the brake booster on the fire wall. The plastic can crack and break, and the two plastic nib that come off to supply vacuum to the rest of the car can crack and break off.

Good luck, I have delt with this problem a number of times with my 300D, 300TD & 240D. Had a vacuum pump go bad, the black plastic tube from the pump to the brake booster go bad and any number of broken, connections over the years. It is alwayse an adventure tracking this problem down.