I don't know if the vaccuum pump on my 350SD is electric or not - does anyone else know for sure?

Which line is the main vaccuum line? I know the one with the red arrow in my photos has oil in it - is that it? What do you do if there is oil in the line?

Don't think the check valve failure would cause a loss of vacuum to operate the climate control flaps.

You need a Mityvac and start measuring vacuum levels at various points in the system........starting with the main vacuum line. You're not getting vacuum to two critical systems..........leaving me with the suspicion that the pump itself might be failing.

How's the brakes feel?

The brakes feel fine - didn't notice any difference at all.
My next question is - where/how does oil get into the vaccuum lines? That might help me understand what's happening.

You do have an electric vacuum pump in the trunk for the doors......but.......it's not relevant to the discussion.

The main vacuum line is the largest vacuum line under the hood. It goes from the vacuum pump directly to the brake booster. There will be several plastic nipples that divert vacuum to other consumers on the vehicle. These plastic nipples might be clogged with oil.........thereby preventing airflow.........and suggesting that there is a system problem, when, in reality, it's just contamination of the lines.

A barrier between the oil system and the air system is breached. This can occur at the shutoff diaphragm on the IP.........or it can occur in the vacuum pump itself.

Start pulling vacuum lines and check for oil. You need to find the source of the oil and correct that problem first.

I just went out and pulled a few vaccum lines by the brake booster and right under the manifold. The lines near the brake booster look clean, but I found that the lines under the manifold seem to be where the oil is in the vacuum lines. There are two line that merge together into one that looks like it goes into the ALDA - that seems to be the source of the oil contamination. That is where we replaced the new cap in my previous photos. It was soaked with oil and soft when we first examined it.

Sorry I'm not a lot of help, but does that help witht he process of elimination?

Am I doing any damage by driving the car?
 

I just want to confirm - am I, or do I have the potential to, do damage to the car by driving it in its current state? The car seems to run just fine - slightly warmer than usual - about 5-10C higher - but it is also over 100F in Las Vegas right now and most driving is with A/C, so I think that might be the reason for higher engine temps.

I just want to make sure that I'm not doing any harm to the engine by driving it with this vacuum leak/obstruction. Yes, it is annoying to have to pop the hood every time I need to shut off the car, but I can deal with that for a little while until I get it fixed.

I was planning to drive my wife's VW Beetle until the Benz is repaired, but we are having transmission problems with the VW, so it seems there is more potential for serious damage by driving the VW than the Benz now!

[QUOTE=Brian Carlton;1523231]A barrier between the oil system and the air system is breached. This can occur at the shutoff diaphragm on the IP.........or it can occur in the vacuum pump itself.QUOTE]

Since I have no problems with the brakes (confirmed yesterday - they are fully functional and there are no signs of oil in the vacuum lines near the brake booster) might that help establish that the problem is more likely at the shutoff diaphragm on the IP? If so, how difficult/expensive should it be to replace the IP shutoff diaphragm?

I've only worked on a 617 but I assume the system here is similar - someone can correct me if I'm wrong.

If the A/C vents went out at the same time, it COULDN'T be the shutoff diaphragm because there is NO VACUUM to that diaphragm when the car is running. If the A/C vents stop when you try to turn off the car (with the key) it could be the shutoff diaphragm, but if they are dead when the car is running, it's a leak or the pump.

Check the pump - you should be getting 15+ inches at the main line. Since your brakes were fine, it's probably not that.

That leaves another subsystem messing things up.
You said the locks worked? I'm not sure if you have an electric pump that is only for the locks, but if you do - good for you, you have no door lock leak. If not, it was leftover vacuum in the storage tank in the trunk (it lets you operate the door locks 5 times between recharges).

That leaves the climate control as the main suspect for the leak. Try shutting off the ACC completely and waiting about 30 seconds. Then turn off the car with the key. If it works, you know one of the climate control vacuum pods has a bad diaphragm (also possibly a bad vacuum line, but probably a vacuum diaphragm).

If it doesn't work, use a mityvac to see if the climate control system main line (on my 300D with a 617 it is green) holds a vacuum with the ACC off. If it doesn't you have a bad ACC switchover valve that is leaking in the off position. Not sure where those are in your car.

Hope this helps, it takes quite some time to firmly grasp the logic behind vacuum troubleshooting. If I was unclear, let me know, I'll try to repost.

Also, this is how things would work on a 617. I have noted all the places I think the 603 could be different - let me know if I missed anything.

EDIT:
This would help you find your leak if it's not the engine, and while I believe this is useless because it is definitely engine related (because of the oil in the lines), I'll leave it.

I'll have to check on the specifics with the A/C, and I will try what you said about turning off the ACC completely, then waiting to shut off. I have been driving in 'Econ' mode - just fresh air, no A/C - and the car still fails to shut off with the key.

However, I now realize that perhaps I have left out some important details...

When using the key to shut off, the car does act as if it is trying to shut off. It definitely slows down and spins down as if it is trying to shut off, but just does not finally stop running. Also, for the last several months my shut off has been longer than it should have been - it would take 2-3 seconds for the motor to spin down and shut off.

Test the shutoff diaphragm with a Mityvac. It should shut right down if the diaphragm is working properly. If it doesn't, then you know the diaphragm is NG.

About the EC mode - in terms of vacuum, it's the same as normal. You're still using the same flaps, just no compressor and A/C.

I may be right or wrong with my post, but even if there is an ACC leak, it won't account for the oil. I'm with Brian, get the line to the shutoff and pull a vacuum on it directly with a MityVac (you do have one, right?). It should shut right off and not leak.

If it's not the shutoff, procede with that ACC test I outlined.

There is a third possibility I didn't mention that seems like it may apply.
If you get to the ACC tests and it doesn't turn off with the ACC off, and the ACC main line is not leaking, it may be a clogged restrictor.
There are restrictors on the main vacuum line where the other systems branch off. These are basically plastic circles with tiny pinholes in the center, the idea being to severely restrict airflow to the accessories. The air can compress enough and flow enough that you still can get good vacuum pressure, but when an accessory leaks, the restrictors keep it from interfering with the brake booster.
Occasionally a restrictor can become clogged. When this happens, you will find that nothing leaks but your engine still will not stop and the A/C flaps either don't operate that you can see or operate very very slowly.
The solution is simply to take the accessories off of the main vacuum line (with the engine off) and use a MityVac to pull air out and blow air in, alternating several times. This will free any dirt that cold be clogging the restrictor and will allow for better air flow.


This would fit with the fact that you have had a 2-3 second shutoff for a few months, but that could be either this or the diaphragm going bad.


Test the diaphragm. If it's good, you know how to procede. If it's bad, you have the problem right there.

Okay - first I have to get a MityVac and then determine which exact line is the one for the shutoff diaphragm. Any suggestions where to get a MityVac? I have read on other threads that a similar vacuum tester is available from Harbor Freight - is it any good? And which vac line goes to the shutoff diaphragm?

On a future preventative note, is there any predominant cause for the IP shutoff diphragm to fail? Any typical cause for it? Does it ever come into contact with fuel? I am just wondering if my hot WVO could have caused it to fail.

Pretty sure it never comes in contact with fuel.
It's just a fairly normal failure as the car ages. Most vacuum diaphragms are that way.

You can get a MityVac at most auto parts stores (I think so anyway) for $200 and below... Wait for another member to confirm that though, I may be completely wrong.
Once you get a MityVac though, you are basically set for forever because it's very solid and when it fails to hold a vacuum, there are cheap rebuild kits with the check valves and seals included.

http://www.tooltopia.com/index.asp?PageAction=VIEWPROD&ProdID=8121&ysmchn=BIZ&ysmcpn=Shopzilla&ysmgrp=Shopzilla&ysmtrm=MIT400 0&ysmtac=CMP&utm_source=Shopzilla&utm_campaign=Shopzilla&utm_term=MIT4000&utm_medium=CMP