I have and old friend ww2 vet that just bought a 77 240d straight stick.The engine will not shut off with the key.I unhooked the two brown lines under the hood and there was no trace of vacum.Would someone send me some instructions so I can fix it for him.Thanks Michael

michael rybikowsky,

You are correct to conclude you most likely have a vacuum leak as the vacuum line running to the top of the rear of the injection pump has a vacuum operated fuel shut off valve. There is a manual method of operating this (so you don't have to stall the engine to stop it) on the injection pump - a lever with a red decal that says "STOP" on it. You just push it down to shut the fuel off.

Since you did not mention that at idle the car smokes excessively, or that the brake assist does not seem to be working I will assume there is at least some function of the vacuum pump left. You should examine the line that runs from the vacuum pump (a kind of bulbous protrusion on the front of the engine, half way down the block on the driver's side with one line leading to air intake manifold on older models (like my '75 and '72) and the other is routed up to the brake booster) to make sure there is no black oil in them. They are normally a translucent white colored plastic. If there is a leak you can still clean the outside, which can get normal grime from the engine on it, but the inside stays black. A leak is an indication that the vacuum pump diaphragm has ruptured and must be replaced. You can also check the function of the brake assist when the car is running and after you shut it off. If there is no vacuum the pedal will be hard to push down enough to make the brakes work.

As is documented in many other threads here, Diesels have no manifold vacuum. Since the brakes and many other functions are run using vacuum in Mercedes cars, like the door locks, as it is free in gas powered vehicles, to use the same gadgets in Diesels you need a vacuum pump.

If your central locks or the brake assist system works, meaning if you lock the driver door (push the driver door button down with the door closed and the car running), the buttons on the other doors should go down and lock the other doors, or the brake assist allows you to get the brakes to work with a normal force appied to the brake, then your vacuum pump is fine. Or at least working. Since the doorlocks work fine using fingers to push them down and pull them up, you may have assumed you did not have central locking. This was standard on all US Mercedes vehicles of your car's vintage, but it was optional on European models. So, if your locks or brake assist system works, the vacuum pump is probably ok, or even if just a few locks work, the vacuum pump is probably ok. By this point in time the vacuum lines and fittings likely have cracks and flaws from age and vibration, so not all of them are likely to work.

Assuming your pump is still ok, then you have some leaks. This will be evident if the locks work with car running but do not work when you shut it off. In some cases the check valve bodies for the vacuum storage system get cracks and leak. If that is the case you cannot store vacuum to do anything once the engine is shut off. These things are little black and green or black and yellow cylinders in the driver side corner of the engine compartment, near the firewall, I believe. My 1982 240D is not here right now or I would check this stuff out before writing this note.

The check valves are pretty expensive from Mercedes-Benz, and the ones from Fords, which are dirt cheap, fit and work fine. Check these by taking them out and

You can check if this is the leak by removing the suction side connection coming from the vacuum pump line and putting your finger over the end. If it draws suction, put the fitting back on, and take the other side off. If the suction is less, the valve body is at fault.

The next thing to do is to selectively block off the various paths to see if the function is restored. This is kind of tedious and the rubber connectors should be considered suspect. Bending them around usually helps to make small cracks visible. These are not really too expensive so any doubt about them and you should just replace them.

The line coming from the vacuum pump is metal as it wraps up around the fuel filter, and I had that unit get corrosion pits that caused it to leak. I wrapped it in electrical tape to temporarily restore the function of the system and then ordered a new part and replaced it.

The last two problems I have had solving this problem dealt with the little actuator on the injection pump, and the connections at the key in the dash. I had some oil in the lines from a ruptured diaphragm in the actuator on the injection pump, which caused the fittings on the ignition key module to swell and fall off. I also got oil leaking into the area under the dash which ran down to the console and onto the carpeting that goes up the side of the footwell to the center console. Over time other vacuum stuff has failed and I just plug the lines now as the little actuators are not cheap and most of the functions the vacuum stuff handles when it works can be performed manually. Even shutting off the engine, but I have not given up on that function yet.

Taking the car to the dealer will likely cost less than a couple hundred dollars to trouble shoot and fix, so if you do not have the tools mentioned above, or the patience to dope this out yourself, it may be worth the fee to have someone check it out and fix it.

Good Luck, Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

Michael:

My brother had the same problem in his 75 300D. We replaced a bad T fitting (not MB) and got the correct line hooked up to the ignition, and it works fine now. Power locks are bad -- broken lines and "amateur" repairs, but the engine shutoff is fine.

The brown with blue stripe plastic line goes to the vacuum source, the brown one goes to the fuel pump actuator.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

I had problems with the plastic vacuum lines that are connected with the short pieces of rubber lines that have gotten old, hard and are not sealing properly.repaced all connecting pieces made big difference.I have also had the drivers side door locking mechanism leak and replaced for engine would not shut down with key.Passenger side door lock was bad and if I remember correctly I could turn key off and lock driverside door and engine would slowly stop. But I would also look at the rubber. All the other post are excellent and should help you get through this.

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83 300 tdt wagon 230,000 mi
85 380 se 31,000 mi
85300 tdt wagon 90,000 mi
84 380 sl 57,000 mi
84 380 se 41,000 mi

sportkar1@hotmail.com
Fairbanks, Alaska

There was another thread addressing this problem. The author suggested diconnecting the vacuum line at the injector and under the dash at the key switch, then using an air hose to blow out accumulated debris in the line.

Remember the debris is going to go samewhere and could make quite a mess under the dash if not properly contained.

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69 220D not running
79 240D parts car
80 240D Beater runs everyday
81 300TD temp disabled cooling problem
82 300SD sweet