1981 300SD No shutoff - how do I find vac leak?
 

Beginning today I have to lift the hood and use the shutoff to stop the engine. A steady look inside did not show me a likely vac leak. I have a Mityvac. What is the easiest way to track down the leak?

Thx.

First, find the shutoff actuator and trace the vacuum line (usually brown with blue stripe) up to a point where it connects to a coupler. Plug your mityvac into it, and carefully pump it up to ~15 inches. If it does not hold vacuum or it leaks down quickly, the shutoff actuator itself is bad.

If not, the next thing up the line is the valve behind the key inside the dash. When in the on position the vacuum from the vac pump is blocked, and the shutoff actuator is vented go atmosphere. Make sure that it true. Next after that is vacuum from the vac pump. If the actuator, valve, and vacuum pump are all OK, you'll have to begin plugging and testing individual vac lines to be sure they are sealed and not cracked. Finally, if all the shutoff lines are intact, you'll have to branch off and see if there are other components that draw vacuum off the shutoff supply line (brake booster hose or the 4 way small line connector) that could possibly be leaking enough to render the shutoff inoperable. The most likely thing is that the actuator itself has a tear in the diaphragm and no longer holds vacuum.

Manny - thanks. Good info. Falcons play tomorrow otherwise should be time to give it a look. Started all of a sudden with no warning. First time in
35 years. I also think it is a large leak because the engine runs strong, is not just barely running and wanting to die with key off.

This would be a good time to check the vacuum pump as well. Disconnect the small vacuum lines from the main line between the pump and brake booster. Plug your mighty vac into one of the lines (making sure any unused lines are capped off). You should show 20 in-hg or so at idle. If it's way less disconnect the brake booster and recheck.

Mach4 - good idea. It was strong about 3-4 years ago when I replaced the tranny but you never know.

Thanks.

You bet. :)

Yes, when my sister drove the 85 190D she called me one day and told me the key did not shut the engine off. It was the original actuator and it did not hold vacuum. I replaced it with the new one and it shut off perfectly. It had no problems prior, and the issue was sudden. If your brake pedal feels like it has power assist, and other vacuum things work OK, the actuator probably has a hole in it and won't hold pressure.

Thanks. Will give it a try.

no engine shut-off
 

Does the door lock system still function perfectly? Is the shifting still right? Is the HVAC still perfectly operational? If any of those is at all weird start with it. The lack of engine shut-off can easily be a symptom of a vacuum leak elsewhere.

Exactly, which is why you test the actuator first and see if it's bad or not.

Will - in the 300SD the vac system for the engine and for the door locks are separate systems - so one will not affect the other.

Manny - is this what you are calling the actuator? Only thing I can find on Pelican.

http://www.pelicanparts.com/catalog/...600284-M22.jpg
http://www.pelicanparts.com/graphics...at_Stars50.gif (1 customer review) Brand: Genuine Mercedes Rating: http://www.pelicanparts.com/graphics/Thumbs5_2014.gif (1981 Mercedes-Benz 300SD Sedan) http://www.pelicanparts.com/graphics/free_shipping7.gif 000-460-02-84-M22 Steering Column Lock
[view in catalog] $19.75 http://www.pelicanparts.com/graphics...art_2014_2.png

The actuator is on the back of the injection pump, here

http://www.peachparts.com/shopforum/...icture767b.jpg

Mach4 - thanks for that. Looks like it also has a rubber hose on it which gives me hope that may be the problem. What is this actuator called on Pelican - how do I find it?

Interestingly enough the SD has all original rubber hoses.

Thx.

1984 Mercedes-Benz 300SD Base Sedan - Fuel Injection - Page 2

Diesel Shutoff Valve http://www.pelicanparts.com/catalog/...702053-M14.jpg

Diesel Shutoff Valve Part #: 000-070-20-53-M14
[ More Info ] Note: Also use- (Qty.) (2) 001-074-20-80 Gasket
http://www.peachparts.com/shopforum/ http://www.pelicanparts.com/graphics...m_supplier.jpg http://www.pelicanparts.com/more_inf...015/SSF/14.jpg http://www.pelicanparts.com/graphics...luestars_A.jpg
Brand Rating http://www.pelicanparts.com/graphics..._shipping8.png $182.50 http://www.pelicanparts.com/graphics...ocart_alt2.png http://www.pelicanparts.com/graphics...ocart_alt1.png

Click for More Info



http://www.pelicanparts.com/catalog/...02053-mini.jpg

Diesel Shutoff Valve Part #: 000-070-20-53-MBZ
[ More Info ]
http://www.peachparts.com/shopforum/ http://www.pelicanparts.com/more_inf...M/MERCEDES.gif http://www.pelicanparts.com/graphics...luestars_A.jpg
Brand Rating http://www.pelicanparts.com/graphics..._shipping8.png $167.50 http://www.pelicanparts.com/graphics...ocart_alt2.png http://www.pelicanparts.com/graphics...ocart_alt1.png

Click for More Info



Pricy little things aren`t they? This is why you grab parts at PNP. Very easy to remove.

If pelican raised the price to $179, you would get free shipping.


Charlie

Wow. Expensive. Hope this is not my problem. Hoping it is just a rubber hose.

Thx.

Yeah, that item has increased in price considerably.

The down side, if you need it, you need it.

Maybe a junk yard item will work, for a while.