Occasional vac issue-a symptom of something? - Page 2 - PeachParts Mercedes-Benz Forum

Maroon 300D · #16 06-13-2006, 12:27 PM

Well, once again I seemed to have a vac leak while driving this morning. The tranny was thumpy like it wasn't getting full vac and while the car shut off quickly, it seemed a little different than normal.

Back to the drawing board, I guess. Oh well, it's really not as bad as the frowny face I put on this post would indicate. At least it's not a serious problem (yet) and it's kinda fun to seek out the problem with my vacuum gauge in one hand and a cold beverage in the other.

SD Blue · #17 06-13-2006, 01:42 PM

[QUOTE=Maroon 300D]Well, once again I seemed to have a vac leak while driving this morning. The tranny was thumpy like it wasn't getting full vac and while the car shut off quickly, it seemed a little different than normal............QUOTE]

It might be a good idea to inspect that check valve again. If it is slightly gunked up, you may be drawing oil into it from somewhere. If I recall, a likely source and maybe a sign the vacuum shut-off is on its way out.

Maroon 300D · #18 06-13-2006, 02:02 PM

Good idea. I may as well take another look as it's pretty easy to get on/off. I wasn't too alarmed at the gunk that was there since the line to my transmission was disconnected for a long time and was plugged up with the same oily gunk.

On second thought, though, maybe what was happening this morning wasn't a vacuum issue at all, since the door locks were all fine. Maybe it was just a matter of getting the trans. fluid up to temp. I do have an 18 mile commute, so it's not as if it wouldn't have time to get warm, but who knows. I do have the first-thing-in-the-morning hard shift issue, but is normally goes away after a few miles.

If it is the shut-off valve, I will learn from the experiences of others and read the posts about installing it very carefully, as I know improper installation can cause the dreaded run-away engine.

Maroon 300D · #19 06-21-2006, 05:26 PM

Well it seems my issues were partly related to the dirty check valve and partly related to something that has yet to be determined. Since cleaning the check valve, the intermittency has gone away. I now have less vacuum when the ambient temp. is ~50 F or less, though. The shifting is a bit rough and the shutdown takes a couple extra seconds.

I figured I must have a leaky connector or something (to the guy who suggested that - I guess I dismissed your theory a little too quickly!) and I saw that the 4-way connector next to the oil filter housing was in pretty bad shape, after all. It definitely had a slight leak but even after replacing it my 'problems' persist. I put the word in quotes because I know how bad it can be to have real problems.

Anyway, I guess I will endeavor to check all the systems and look at the check valve again for oil, just in case my shut-off valve is going, though I doubt it is. I think I will start with the EGR. I'm not sure if it's connected or not...I'm guessing not because I get 25 mpg and it's a CA car.

My EGR connections are not on the valve cover, BTW. The CA vac system is a little different.

I don't suspect the booster hose or the valve on it because they are practically brand-new. I don't suspect the door lock system because the locks all work fine when the car shuts down normally.

I should be able to figure this out and I will post the results when there are results to post!

Maroon 300D · #20 06-22-2006, 10:49 PM

That's kind of odd, isn't it? I thought it was supposed to be 15hg...and at full throttle it only goes down to 13hg.

I wonder if a the CA cars with the blue transducer are different in that respect for some reason? I wouldn't think so, and so far I haven't been able to find anything that confirms that...

SD Blue · #21 06-23-2006, 10:12 AM

That high of vacuum, makes me wonder if the restrictor is missing. There should be a small restrictor in the vacuum line leading to the tranny.

Maroon 300D · #22 06-23-2006, 11:14 AM

I didn't know there was supposed to be a restrictor. I believe there is no restrictor in my line.

The '85 vac system is different than the other cars, though. I'm not sure but I think the CA cars are even more different. It seems that uncharacteristically, there's not a lot of info. about the vac system I have here...it's evidently kind of a mystery.

I wouldn't be surprised if the blue transducer, where the line to the tranny originates (well it doesn't 'originate' there, but that is the last stop before the tranny), is supposed to serve as the restrictor on my car.

On a positive note, I seemed to have normal vac this morning. Funny, A few days ago I replaced a leaky part and no difference...Two days ago I plugged the EGR line, as the EGR wasn't holding vacuum, still no difference...and yesterday I replaced nothing, all I did was test, and this morning it works as it should!

Actually it shifted a bit clunky at one point, when I had the heat on...but previously I had run the climate control in all difference modes and it seemed to make no difference in how the car ran.

to be continued...

my123ca · #23 06-23-2006, 11:51 AM

[QUOTE=Maroon 300D]Well it seems my issues were partly related to the dirty check valve and partly related to something that has yet to be determined. Since cleaning the check valve, the intermittency has gone away. I now have less vacuum when the ambient temp. is ~50 F or less, though. The shifting is a bit rough and the shutdown takes a couple extra seconds.

You might want to check your vacuum transducer switchover valve. It could be dirty and getting stuck. This valve is controlled by one of the coolant temp. sensor. It is found behind the brake booster in the firewall. You would also want to check the three way check valve, leaks sometimes even if looks new.

Maroon 300D · #24 06-23-2006, 12:17 PM

Quote:

Originally Posted by my123ca

You might want to check your vacuum transducer switchover valve. It could be dirty and getting stuck. This valve is controlled by one of the coolant temp. sensor. It is found behind the brake booster in the firewall. You would also want to check the three way check valve, leaks sometimes even if looks new.

Yes, the electric switch over valve...do you know how to test this? I guess I could see if it holds vacuum if nothing else.

I was wondering what the heck those things (there are two of them, the other one is next to the gizmo that sends a line to the EGR) do. I was thinking they weren't connected to the coolant in any way as the non-vacuum lines that attach to them both appear to run through the firewall near the fuse box, but I don't doubt your description, either. Certianly, it makes sense and I thought there was some sort of vacuum/temp. device.

For those who aren't 'in the know,' the valve 123ca is describing has three vacuum lines attached to it. If memory serves correct, two of them come from the line that heads toward the green damper that sits in front of the white vacuum control valve and one runs to the transducer.

As for the three-way check valve, I assume you're talking about the yellow valve that holds vac in the door lock system; I tested it and the lock/unlock systems yesterday and found no leaks. I tested the modulator, too, and it only lost 1" hg in five minutes (16.5-15.5), so I would think that's acceptable.

By the way, thanks for the info.! Like I said, vac. info. for this specific car is a little harder to find.

SD Blue · #25 06-24-2006, 01:08 AM

Quote:

Originally Posted by Maroon 300D

..............
By the way, thanks for the info.! Like I said, vac. info. for this specific car is a little harder to find.

Try here:http://www.peterschmid.com/vacuum/1977_1985/617_95/1985_cal.jpg

Maroon 300D · #26 06-24-2006, 05:19 PM

Thanks for the link. I do have that already, though. The lack of info. I was referring to was more about the exact functions of some of the gizmos, particularly the electrtic switch over valves, the transducer, and the thing that sends a line to the EGR.

It looks like on cars with the transducers, the tranny vac can maybe be adjusted on the transducer instead of at the modulator. If true that is one nice feature, at least.

SD Blue · #27 06-26-2006, 11:23 AM

http://mb.braingears.com has 17 pages on the operation of the EGR system. Does it not cover this?
(I know, the site can be a little difficult to access at times. Especially if you are using dial-up.)

Maroon 300D · #28 06-26-2006, 12:07 PM

I have that on CD. Maybe I'll have to look at it a little more closely - some of the info. can be hard to find as the heading things are under isn't always obvious. I don't remember seeing much about the nature of the various vacuum components, though.