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  #1  
Old 09-03-2016, 08:10 PM
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I know this has been addressed a lot...300D won't shut off

Hello all,

I'm pretty sure my monkeying with my '84 300D turbo diesel vacuum lines has made things worse...

My vacuum door locks have never worked quite right and I tried digging into them just a few days ago. Now the engine won't shut off from the key. The way I DO stop it is by putting my finger over the inlets on the yellow check valve that goes to the reservoir and I believe master door switch.

Since it stops when I do that (and my main question here before I tear into the door) could the hose have become disconnected behind the door panel? I don't know enough about what air goes where to figure it out. I feel my brown and brown/blue lines going to the switch are tight.

Thanks for any help!
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  #2  
Old 09-03-2016, 08:29 PM
dieseldan44's Avatar
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Location: Boston
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any number of things could be going wrong - but you have a large vacuum leak behind the yellow check valve in the locking system.

if you are dedicated to solving this mystery your going to need a MityVac.

search terms:
vacuum reservoir
master vacuum switch
vacuum lock pod rebuild
vacuum trunk lock
fuel tank vacuum lock

the strategy is isolating each door and lock one at a time and checking them. it's not that bad - people make way more of it than it is. take time to understand the system before tearing it down:

this thread, in particular post #5:
W123 Vacuum InterLock Diagram

good luck -
dd
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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car
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  #3  
Old 09-03-2016, 08:39 PM
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Well, it is good you did find a way to stop the engine. You possibly are not familiar with the "red" painted lever on top of the injection pump is there to stop the engine, but you do have to open the hood to get at that. Typically in your problem one of the brown vacuum lines that control this is off. The brown line comes off the main vacuum line just in front of the brake booster and from there it goes to the ignition switch (valve) which is built into the back of the ignition switch. When you turn the ignition switch off, the vacuum switch is open and allows vacuum to pull the rack to stop the fuel. So, since you have a problem in the system, there is I think only two take off points before the vacuum brake. These are the two small out let tips quite close together. If you use one for the vacuum shut off and stop the other with a small piece of hose with something like a golf tee or any thing you can get into it so it doesn't leak, (suck in air) then your engine stop should work. It should function even if the other small tube is open - it should. But these cars are getting older and I don't know how good your vacuum pump is working. If it is working correctly there is ample vacuum to do that and more. So isolate the one nipple and work only on the engine stop. It goes from the main line to the ignition switch, then from the switch to the shut off valve. It is really quite simple. Make sure there is nothing else tied into that dark brown/blue line.
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1983 Mercedes W123 240D 4 Speed 285,000 on the road with a 617 turbo, beautiful butter yellow, license plate # 83 240D INDIANA

2003 Jaguar Type X, AWD. beautiful, good mileage,
Mom's car, but I won't let her drive it!
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  #4  
Old 09-03-2016, 10:57 PM
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Thanks for the help! Just to test it, I took the yellow check valve out and put a golf tee in its place and the car now shuts off correctly. Barring door locks, is it safe to drive the vehicle like this? Really don't want to tear anything up, but plan on checking the door locks soon.

BTW, I tried killing the engine from the red "stop" switch and it sounds like the engine is trying to stop, but never stops dieseling. Is there an adjustment or do I need to check vacuum?
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  #5  
Old 09-03-2016, 11:10 PM
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Location: central Texas
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That red stop lever should be the direct mechanical link to the fuel shut off... not something which activates something else which requires vacuum to work... so yes, I think an adjustment of that is in order... that IS the emergency , if nothing else works, shut off..
I have looked at my 616 FSM but can not find exactly that information..
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  #6  
Old 09-03-2016, 11:12 PM
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Quote:
Originally Posted by Amphiduck View Post
Thanks for the help! Just to test it, I took the yellow check valve out and put a golf tee in its place and the car now shuts off correctly. Barring door locks, is it safe to drive the vehicle like this? Really don't want to tear anything up, but plan on checking the door locks soon.

BTW, I tried killing the engine from the red "stop" switch and it sounds like the engine is trying to stop, but never stops dieseling. Is there an adjustment or do I need to check vacuum?
It is safe to drive without the locks, but definitely not safe to drive without to stop level functional!

you need to adjust the accelerator rack system to allow the stop lever to have enough travel to cut fuel to the engine. id take the time to adjust all of the throttle levers to the correct lengths as specified in the factory service manual. i believe the Haynes manual has a diagram as well.
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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car
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  #7  
Old 09-09-2016, 07:51 PM
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Location: Philadelphia PA metro area
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I don't know your history and plans with that car, but shortly after I got my 240D the lock actuator inside the left rear door developed a leak, which of course prevented engine shut off. After tracking it down and fixing it I thought about it a while and decided power locks just didn't mean that much to me so I capped off the vacuum line to the body (which addresses the door locks and trunk lock). Simply disconnect it and stick a golf tee in each end of the line (to prevent a vacuum leak on one side, and to keep dirt and fluids out on the other side). Your preferences may be different, I was looking for the fewest possible mechanical issues on a 25-year-old car (now almost 35 years old).
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