Vacuum woes
 

300D 1983.

I seem to have some vacuum issues and was hoping someone could point me to the right page here. (searching for Vacuum doesn't help).

Is there a simple way in the engine compartment to isolate the various parts of the vacuum system in order to isolate the leak? I know that the climate control, locks, brakes, fuel delivery, and transmission all operate off this system.

Issues:
Door locks worked two days ago, now after letting the car sit for a few hours, all the door locks do not open.

Poor fuel delivery - car surges at low speeds (slow/fast)

Transmission is shifting poorly.


I know when everything is working well on the car, it does none of things and runs really strong.

Thanks
Doug

PS. I thinks its the EGR valve, has a rubber hose that a hard plastic vacuum hose goes into. The rubber hose is falling apart. What can I replace that with?

It sounds like something has just come loose if virtually everything isn't working...

The in built search function is not very good.

Try something like this in google

vacuum door lock site:peachparts.com

Otherwise you'll see many vacuum related threads in the DIY section

PeachPartsWiki: Do It Yourself Articles - Mercedes Vehicles

Do you have a Mity Vac tool?

When you turn the key off, does the engine shut down as it should? (there is a vacuum actuator on the IP)

The fuel filler vacuum pod was the weakest link in the system.

Everything shuts down fine. What is the fuel filler pod?

I would pick up some vacuum hose from the parts store and replace the EGR line. Then do a visual inspection of everything you can see.

I had vacuum woes on my SD and found that this helped me isolate the different circuits:

http://i711.photobucket.com/albums/w...f/SANY0056.jpg

Those little black "spider" deals get old and leaky and they don't improve after manipulating them during troubleshooting.

Good luck! Since everything was working before I'm sure you'll find it's something simple!

Start by measuring the vacuum at the main line with the Mity VAc. If the vacuum is ok at the main line with the engine running, your vacuum pump is ok. You then need to pull a vacuum on the yellow line and then the green line. Yellow is locks, green is climate control. Pull the vacuum and see if it holds. You should get an answer with those three tests because it appears the shut-off system is fine if the engine is shutting down ok.
I'd check the lines that go the Vacuum Control Valve to control the transmission on top of the IP, since if you are getting hard shifts, you have low vacuum in that system.

If I were to put a vacuum gauge on the system, how much vacuum should I see normally?

Around 21 inches at sea level. Lower at higher elevations.

Here is a list of vacuum diagrams.

http://www.peachparts.com/shopforum/diesel-discussion/105297-vacuum-diagrams.html

http://www.peachparts.com/shopforum/diesel-discussion/160169-w123-vacuum-interlock-diagram.html


I doubt your EGR even works, probably plugged solid.
Charlie

For the 83, the best place to start checking is on the engine side of the firewall by the brake booster. Everything branches from there.

Search function here could be better, but isn't that bad if you do an advanced search (I never use the basic search function). The basic search will search the whole content of all posts for the keywords you enter. If you do an advanced search you can narrow your keyword search to just titles, which is what I always start with and usually have success finding what I need (just have to think about how others will title threads related to the topic of interest). You can also tailor you search in other ways as well and sort the result in different ways.

I believe the search here is limited to returning up to 500 results, which is what you get if you search those words. A google search of those criteria returns over 10,000 links. A forum search (titles only) returns 29 results.

The key is picking the most relevant search terms, which sometimes involves thinking like other forum members. Of course, if you've been around long enough, you can also search by member if you know who probably has the answer you need.

Also if you use parentheses to bracket words you can search phrases. Whereas a search of the words "fuel" "hard" and "lines" will return a bunch of threads that just contain those words someplace in the text, a search of "fuel hard lines" will return far fewer threads that actually contain those three words together.

To me, the worst part of the forum search is the 20 second wait between searches, what's the deal with that anyway? Sometimes I want to try a phrase, but if I don't get what I want I would like to go back and try something else . . . . but you end up waiting until it's okay to search again. 15 or 20 seconds doesn't sound like much, but in the age of high-speed information, it is nearly an eternity. :rolleyes:

I built a custom thread with diagrams and pics combined. It may not be exact for your car if it's a Cali model. The diagrams are also for a coupe, so they have an extra line for the seat backs. http://www.peachparts.com/shopforum/diesel-discussion/295616-definitive-83-fed-300cd-vacuum-thread.html

Generically in the engine bay green is climate control, yellow is locks, white (light gray)is the engine. Check valves may/may not isolate these systems depending on whether the engine is running or not.

Uber-basic troubleshooting may be simply playing with the AC controls: do the symptoms go away in OFF, in DEFROST, etc. You may be able to isolate a leak there.

A to Q. from above: Fuel filler pod refers to the vacuum pod that activates the pin in the door over the fuel cap. It's connected to the locking system (yellow lines).

Where did you find the 5 way and the 4 way in the photo? Looks like a neat replacement for the black ones.

Here ya go Joe:

List: Vacuum Connectors - Straight | O'Reilly Auto Parts

I think they were in the "HELP" section near the rubber vacuum caps.

In this pic I vave the vac hooked into the blocked off port (for the gauge) and a vacuum pump made from a breast pump :eek: and some radio shack bits hooked up where the engine vacuum pump supplies vacuum.

http://i711.photobucket.com/albums/w...f/SANY0029.jpg

It works well for troubleshooting vacuum stuff with the engine off. A better option would be a Ford truck electric vacuum pump but they are about $100.

I have dumb question. In the picture on the 4 way vacuum splitter, there are pieces of black hose that accept the Mercedes hard vacuum hoses. What are these black pieces of hose called and where can I get some? My EGR adapter hose is frayed beyond, so that vacuum hose keeps popping off.