Won't shut off..........W115.... - PeachParts Mercedes-Benz Forum

KylePavao · #1 01-12-2008, 09:38 PM

Hey guys,

The 300D has started to not shut off again. I replaced the switch under the dash, and replaced vacuum lines. Worked great. For awhile...

I think it is the shutoff valve. However, here is my question: For the W115 chassis, no part is listed on Fast Lane. Is it the same part as a W123 300D non turbo? Also, I don't see any bolts for removal on my parts car. Anyone know any W115 specific information for this problem?

My hypothesis is this: I replaced vacuum lines, and the switch under dash with clean new lines. The shut off valve slowly continued to allow blowby oil to enter, and eventually gummed it up again. Hence the reason it does not work again. Any thoughts?

I read the DIY for replacement, and it looks easy. Just curious on any specific W115 info.

KylePavao · #2 01-12-2008, 11:50 PM

Bump?

kerry · #3 01-13-2008, 12:39 AM

Put a Mity Vac on the thing and pull a vacuum to get the answer to your question.

KylePavao · #4 01-13-2008, 06:26 PM

It seems the shutoff valve on the pump isn't working. But where to get the part? Same as W123 300D/NA?

Also, it seems to shut off when I rev the engine a little bit.

I attached a vacuum pump directly to the shut off valve on the injection pump, it works. However, when I go through the underdash switch using the vacuum pump, it doesn't work. So you know, the switch is a used one from amother car. Any thoughts?

LUVMBDiesels · #5 01-13-2008, 06:49 PM

Quote:

Originally Posted by KylePavao

It seems the shutoff valve on the pump isn't working. But where to get the part? Same as W123 300D/NA?

Also, it seems to shut off when I rev the engine a little bit.

I attached a vacuum pump directly to the shut off valve on the injection pump, it works. However, when I go through the underdash switch using the vacuum pump, it doesn't work. So you know, the switch is a used one from amother car. Any thoughts?

Put the pump on the line from the switch to the valve and see if it works when you bypass the switch. then put the gauge on the line from the vacuum pump to the switch and see if you are getting vacuum. If the engine shuts off when you bypass the switch and you have vacuum from the engine bay the switch is bad. You can get the switch from Phil for $25.

KylePavao · #6 01-14-2008, 05:00 PM

I replaced the underdash switch to try to alleviate my no shut off problem...to no avail. My next thought is the vacuum pump. I am going to order the repair kit for the diaphragm and the valve. My question is this: can the vacuum pump simply not being creating enough vacuum, while the brakes and vacuum controlled AC components still work properly? I'd imagine if the pump needed to be rebuilt, then my brakes would require much more effort to operate properly. Check valve also has been pointed to as a possible problem.

#7 01-14-2008, 05:03 PM

I very much doubt the vacuum pump is the issue if all the other vacuum devices (especially the brakes) are working correctly. Does it shut off if you apply vacuum directly to the shut-off valve?

kerry · #8 01-14-2008, 05:07 PM

I'm pretty sure he said in the other thread that it did. Before ordering any parts, I'd start taking vacuum measurements at various points in the system to determine what is going on. Measure at the shut off, at the main line, at the branches for the door and climate control etc.

KylePavao · #9 01-14-2008, 06:24 PM

Umm it does shut off if I apply vacuum to it directly via a compressor driven vacuum pump. However, when I route my compressor driven pump through the switch, I cannot shut it off. Yet, all my systems work. I need to think this out further. It used to shut off when I revved the engine slightly before shutdown, but now this technique only works sometimes.

I am inches from running a cord from the shutoff lever to the inside of my car

tangofox007 · #10 01-14-2008, 06:30 PM

Do you have any idea how much vacuum is required to actuate your shut-down valve?

KylePavao · #11 01-14-2008, 06:40 PM

25mm/hg...pretty sure

Also, when I apply vacuum to the green line going to the shut off at the injection pump, with the engine off, I can hear sounds coming from the vacuum pump. Should air be going through here, or are the valves inside supposes to stop it

JimmyL · #12 01-14-2008, 06:45 PM

I'm going to have to assume your late W115 is the same as a W123. {Don't know this, just guessing from info above.}
If you apply vac straight to the shutoff valve and it shuts off, the valve is fine.
If you remove all other vac destinations and run it only to the switch, then from the switch to the shutoff valve, then either the switch is bad or there is a leak in that part of the vac circuit.
You simply HAVE to have a Mityvac if you own these cars, and it is a very modest investment too. That way you can trouble shoot and won't have all the guess work.

***
BTW, I think the shutoff valve works with just a shade under 10 {insert vac units here}
Why would you be supplying vac to the injection pump with the car off? Doesn't tell you much as this doesn't happen during normal operation.

**********
Another BTW, looked at your car in your gallery, and that is a beautiful W115!!

kerry · #13 01-14-2008, 07:21 PM

On a 123, the vacuum line going to the shut off valve is brown, not green. Not sure whether this observation has any relevance at all to a 115 but it would seem odd for MB to switch standard colors from model to model.

tangofox007 · #14 01-14-2008, 07:34 PM

Quote:

Originally Posted by JimmyL

If you apply vac straight to the shutoff valve and it shuts off, the valve is fine.

If it is taking 25" Hg to actuate the valve, something is wrong. The vacuum system on the car typically can't produce that much vacuum.

KylePavao · #15 01-14-2008, 08:53 PM

Alright, here are my vac gauge readings:

At the T from the vacuum pump, I am reading 55 CM of Mercury. Thats what the gauge says. I am not ****ting you.

From the green line running from the switch to the shutoff valve on the pump, with the ignition in off position, I am reading 48-50 cm of mercury. I have a ton of vacuum.

Here is the problem: with the mityvac, running directly to the pump, it shuts down with only 25 cm of Mercury. With 50 cm of mercury it shuts down.

However, when I attach the line from the switch (which I KNOW is pulling 50 cm of mercury), the stupid car will not shut off! The car ONLY wants to shut off using the mityvac. Bypassing the switch it will not shutdown, unless I rev the car lightly.

So I have a working vacuum system, I am producing vacuum, and the switch works. In the on position, the lin to the shutoff from the switch reads zero. When I turn off, the line is reading 50 cm of mercury.

This is the most bizarre problem ever, and doesn't make sense to me whatsoever. The car does not want to shut off under it's own vacuum.

Any input? It baffles me. Especially when my system is producing more vacuum than the mityvac needs to shut the stupid car down.

Thoughts?