I bought this '95 E300 Diesel (124 body) a year ago from a Mercedes Dealer. The car came with a rebuilt engine by Mercedes. Slowly but surly over the last year I fixed all the small things that were obviously defective with this car except for one.

The one thing that still does not work, and I can't figure out why, is the emergency shut-off knob on top of the main fuel filter.

The engine is supposed to shut-off when you turn this knob clockwise, (as per owner's manual and per direction on the knob itself) except when I do that nothing happens. I turn the knob all the way in and the engine keeps on running perfectly. I removed the valve assembly and inspected the valve, its a very simple valve mechanism that is supposed to shut-off the fuel when turned clockwise, it works fine. there is nothing wrong with the valve, yet the engine still does not shut-off.

I tried it by simulating a vacuum leak and shutting off the ignition. Engine kept on running. What can be wrong. How can I shut off the car if I do develop a real vacuum leak.

The fuel filter into which this valve fits is the original Mercedes fuel filter. Could something be wrong with the filter itself?

I am stumped

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'95 E300 Diesel, 264,000 Miles. [Sold it]

If it is before the IP, and ONLY stops fuel flow, then it ought to turn off the car, but it will take a while. Apparently the IP holds quite a bit of fuel in itself. This fuel will partially be returned to the tank, but some of it I suppose will keep on being injected into the engine.

Have you tried turning it the right way and then letting it run for a minute or so?

From your descrioption, I wouldnt say its like the w123 shutoff, and therefore doubt that it would be so instantaneous.

JMH

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

I have not idea what is the wrong with the shut off valve. However, to stop the engine, simply stop air from entering it. I put a new K&N filter on my 409d last week and putting a plastic shopping bag over the filter shuts it down in about 2 seconds.

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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 have run the car for a week with the valve supposedly in the shut-off position. Car still run fine.

I'll try the shopping bag trick. I can't try it however on the inlet to the air filter since the air filter takes its air from the slits in the passenger side fender, and its impossible to create a good air seal there.

I could try however blocking the air between the output of the air filter and the intake manifold by removing the tube connecting the two. I'll have to be careful that the thing does not get sucked into the manifold.

I would however prefer to find out what the real problem is and then fix it.

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'95 E300 Diesel, 264,000 Miles. [Sold it]

I don't know what the slits in the fender look like, but putting a garbage bag over the slits should cause it to be sucked up tight to the fender, sealing itself.

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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

Blocking the slits on the outside of the fender will not work, since there is a 2" gap between the slits and the actual intake for the air filter. Air will still come in through this 2" gap.

By the way, the air slits that I am talking about are actual slits on the outside of the passenger side fender. Only E300 Diesels have those slits in the fender.

Non-Diesel 124 body cars, such as the E320 do not have those slits.

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'95 E300 Diesel, 264,000 Miles. [Sold it]

Not a good idea...
If you are going to do that, use something hard and flat like a phonebook or thick cardboard, don't use a plastic bag post airfilter. It's not worth risking a head-off repair to see if you can asphyxiate your engine.