ENgine will not shut off on my 1984 Mercedes 300D turbo

In that article that Richard linked to it mentions sucking on that line. If ti takes 15 to 20 pounds to get it to operate, I don't think that you can do that with your lungs. but I might be wrong. Either way, I'd suggest getting a short section of rubber hose and sliding that over the end of the hard plastic line and sucking on that instead. I use an old syringe like you get with epoxy to troubleshoot vacuum systems. On my 300D the vacuum line was actually at fault. The rubber connections will start to leak once they get old. Although that might also be aggravated by exposure to various things. I just put new rubber connections everywhere I could find and everythign started working better. The vacuum system does everything in that car.

I've been meaning to ask; if I hook a vacuum pump to the shutoff valve and give it a squeeze, the car shuts right off. When connected "normally", shutting off the key results in the car stopping after a couple of seconds, so it seems the vacuum eventually gets there when left to its own devices. What parts in the system might I start looking at? Richard's article says that the vacuum hose goes to the ignition switch, is that relatively easy to access if the kick panel has been removed under the dash?

thanks,

-tom!

Pounds of vacuum?!?

In the USA, vacuum is measured in inches of mercury.

If you can do 7 pounds with your lungs, then you can suck a golf ball thru a garden hose :)

This is really hard to do without a vacuum tester. You can get a "Mighty Vac" (or some silly name like that) from any half-decent car parts store. There's two versions, the plastic one and the metal one. The plastic one is to be considered disposable; get the metal one.

What you'd do it test the system bit by bit. There's not really a lot to it and what you're most likely going to find is a black rubber connector that has an almost imnpercevable crack and that's letting air in.

You CAN test this without a tester but it involves sticking tubing in your mouth and sucking. Hope you like the taste of oil :-(

garden hose :)

I don't remember details, whether it was pounds of mm or Hg.

Yeah, that's what I meant when I said "vacuum pump" above. ;)

Ok, I'll dig in. Ugh good times. My day under the passenger carpet was not fun, but that was 'cause I didn't know what went where (and was disappointed to find that the vacuum parts all worked, but there were other things that have cause the automatic locks to not function). I suppose it could be worth it just to get a bunch of those junctions and go through and replace 'em all as I come across them, huh?

-tom!

It probably is. Look around under the hood and pay special attention to all the rubber connector. Take each one off, examine it throuroughly and put it back on.

The cynical view has it that the mere act of taking them off and putting them back on will cause them to fail. But the connectors are cheap at the dealer. It really wouldn't hurt just to replace them all.

Be aware you cannot get color coded vacuum lines any more, just black. Also, the tubing sometimes fails at the juction of the connector so sometimes you have to cut it back half an inch or so.

If your door locka aren't working anyway you probably ought to just plug up that branch of the vacuum circuit with a screw (don't use a golf tee, they fall out)

Dollars to donuts though it's under the hood and easily fixed.

K, thanks.

I'm of that mind also, especially considering they've been there for almost 30 years.

Yeah, I've wondered about this; are there different diameters at play in this car, or are they all the same size? Autohaus has different colors available, it seems, but I haven't bothered measuring the ones on my car to make sure they'll work. Certainly, if I can at least get almost the right color, I'd prefer that to black.

I intend to fabricate the springs. One of these days. ;)

Excellent, I'll take a peek. First stab will be to put the vacuum tester on the vacuum hose and shut the car off. Somehow I didn't even think of doing that when I was fiddling with it last time...

thanks for your insight,

-tom!