I have a 1984 300D Turbodiesel with a vacuum leak nightmare! I have conventionally tested all lines coming from the firewall. Tested the green line which goes to the climate control- held vacuum. Tested the fuel shut-off valve directly where the brown line goes- holds vacuum. Tested both yellow lines that go to the doors- both held vacuum.

However, there are two black lines that go into the firewall. One comes form the Vacuum Control Valve (VCV) into the firewall, but is not connected to anything under the steering column inside where firewall is found.

The other black line going into the firewall comes from the Vacuum Converter, but it is not connected to anything inside under the steering column. I understand one of the black lines going into the firewall is an air vent that is not connected to anything, but i don't think the car has two vent lines.

I also recently replaced the vacuum pump and tested it which generates proper vacuum to the hose that is connected to the brake foster. This line was also replaced with new one. In addition, I have also replaced the VCV and have replaced all rubber connections any Y rubber connectors!

In spite all efforts, vehicle still does not shut off! Well it shut offs immediately when it feels like it. Meaning on occasions it shuts off, while others it does not.....:-(

Can anyone share any light to the vacuum nightmare?

Is the shut-off valve itself good? When you apply vacuum to it, does the car shut off?

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 157k miles
06 E320 CDI "Rutherford", Black on Tan, 175k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 144k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 70k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

Thank you for responding!

shut off valve works! tested it by plugging in vacuum pump directly to valve, turned on car and pump vacuum to it...and immediately shut off. Hence, shutoff valve is in good standing. Do you know anything about the two black lines that go into the firewall, they are not connected to anything inside.

You need to T a vacuum gauge into the system and monitor it to see what is going on when it doesn't shut off. It could be that you tested the green climate control line when the climate control was in a certain condition and then when the climate control goes into another condition a vacuum pod leaks. I'd simply block off the yellow and green for a while and see if everything works fine. If it does, then hook one up and test it, then the other.

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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

If you connect the brown line and nothing else to your vacuum source the car should shut off. The brown & yellow(?) line goes from the shutoff valve in the car to the pod on the IP.

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'70 F100 shortbed
'82 Diesel Westy
'83 Euro 300TD
Curtlo Viper
Yeti ARC
Surly long haul trucker

thank you kerry and fattyman!! I will block off the green and yellow lines tomorrow and cruise it for a while and see what happens. Also, do any of you
know where the two black lines that go into the firewall are connected to? They are disconnected and don't know where they go? I understand one is a air vent, but the other? my cruise control is not vacuum as I see its electric as I checked the steering column and didnt see a vacuum line for it. It's a 1984 300d W123 chasis turbo diesel.

I would begin by measuring vacuumed at pump.if that is good,then block off each line one at a time ,yellow green etc with golf tee and see if car shuts down.isolate the system that leaks,then try to find leak.

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95 e320,87 sdl,79 300sd

thank you all for your responses....
After all efforts of checking each vacuum line and plug a few to determine where the leaks was located...i could not locate the leak, hence called a local mechanic. In a few minutes the mechanic was able to locate the leak! As it appears there is a fuel filler door vacuum element and is not properly working. I did not even know the fuel door also closes with vacuum, as i just thought the fuel door was never locked and was normal. Apparently the fuel door locks with a vacuum element as to secure the fuel tank. Therefore, I will have to replace such part to solve the nightmare door leak! Also, the two black lines that go into the firewall that are located under the steering wheel are vacuum vents that are not connected to anything.

thank you all for the support and guidance....

one

mecatli