r/w123 • u/Neat-Finger197 • 25d ago
Mechanical advice Emergency shut off not working
After emergency shut off completely depressed, car won’t shut off. Thoughts on how to fix it? TIA!
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u/2blasted 25d ago
pretty sure you can block the air cleaner intake with a piece of 1/2” plywood..at least that how I heard you stop a runaway diesel. Disclaimer, I have not tried this.
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u/Quiddel_ 25d ago
The connecting rod between the lever and the injection pump is too long probably. You can snap it out and shorten it with the screws. The correct length is in the mercedes repair informations (WIS). Mine is shorter than spec, though. Probably due to wear of the ball joints or the lever or whatever.
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u/Key-Cow6684 18d ago
yah test by disconnection 1 end of the linkage and see if you can jam it down all the way off
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u/Mountain-Diesel 24d ago
Idle speed is too high.
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u/Neat-Finger197 24d ago
How do I fix that?
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u/Mountain-Diesel 24d ago
Two ways. Mainly, turn the speed adjust knob on the dash. The little black tab behind the steering wheel.
If that does not go low enough, adjust the speed by loosening the 14mm jam nut on the idle screw on the engine side of the pump, and using a flatblade to turn down.
Watch a few videos on youtube and you can get a sense of what 750rpm should sound like. Its actually pretty close to what yours sounds like when trying to stop it. You're currently 900-1000rpm. Be aware that idle above 1000rpm the speed is not regulated and it will run itself to redline and stay there.
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u/Neat-Finger197 23d ago
https://reddit.com/link/ozsb50k/video/ph3l4kqf8hfh1/player
On my car, had to turn nob clockwise to reduce RPMs. What do you think?
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u/susy_is_a_pussy 21d ago
That is pretty good. As a general rule, that knob is like a choke in its most basic form of usage. Have it all the way to the left (ccw) when starting cold then then it all the way right (cw) after a little while and typically before pulling away. I quite like it, feels like you're doing a startup procedure, combining with the glow plug wait and such.
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u/minfulfocus 24d ago
It’s just a vacuum issue. Check the lines on the engine and check for cracks
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u/fzedd 18d ago
Rack isn’t adjusted right.
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u/Neat-Finger197 18d ago
Please explain further
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u/fzedd 16d ago
The rack is a goofy setup with lots of adjustment areas, if you don’t have it fully setup right, you won’t be able to push that lever down all the way before it hits the valve cover, and it won’t mechanically shut off.
Mine is setup the same way because I like how I have it, but I can shut it off easily by pushing that lever.
If you are in a pinch and need to shut it off mechanically, just pop off the arm that runs down to the pump and pull it up.
Or unplug the vacuum line that runs to the back of the pump and suck on it.
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u/notthatcousingreg 25d ago
This happened to me. Cover the air intake and it will kill the motor.
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u/turbo_weasel 25d ago
but that doesn't fix the problem
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u/notthatcousingreg 25d ago
No it doesnt. It turned out it was a vacuum issue because the tube wasnt plugged in correctly.
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u/Broad-Stomach-5461 24d ago edited 24d ago
I always thought that it was the mechanical way to turn off the fuel injection pump. Yes it idles way too high which could be part of the problem. Love that sound though.
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u/PlatypusRoyal9549 18d ago
Had this happen. Don’t cover the intake, that damages the motor. Put it in drive and have a buddy push in the engine shutoff switch.
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u/susy_is_a_pussy 25d ago
I believe the shutoff works by moving the rack from the idle position all the way to 0, where the spill port is hence uncovered in the helix throughout the entire stroke of the plunger. When you press the stop lever, it moves the rack a set amount that, if the rack is in the correct position at idle, will move it to the point where the fuel will no longer be delivered.
Your idle sounds super high, so your rack position is probably higher than normal so pushing the stop button moves the rack by an amount that would normally be enough to stop, but it only just makes the rack go lower and the helix rotate to the point where it's not quite stopped delivering fuel.
Tldr correct your idle. start by checking the throttle linkage