Vaccuum thingy question? - PeachParts Mercedes-Benz Forum

cewyattjr · #1 08-31-2008, 10:42 AM

See photos below. I'm looking at troubleshooting a rough transmission shift. The levers seem in good shape though they are probably original so will replace. I noticed that one line from the lever assembly goes over to this valve which I wasn't able to identify in the sticky-posted vac diagrams.

What is it? Is it a problem/leak that there seem to be no line going out the other side. It is simply supposed to go to the EGR valve? I have no line on that, and would that account for enough vac lost for rough shifting?

Thanks,

Chuck

Diesel911 · #2 08-31-2008, 10:59 AM

I replace the ones (2/3 Way Valves) on my car to the tune of over $40. Later on; on this Forum I learned that those valves are there to control the EGR system. Meaning that except for being a possible source of a vacuum leak they do not effect the transmission.
This is not a recommendation but people disconnect their EGR vacuum supply and remove those valves.

As for checking the Vacuum part of the transmission control there are quite a few Threads on that subject and also harsh shifting. The Vacuum part involves the white plastic valve on top of the rear of the Fuel Injection Pump and the Vacuum Modulator on the side of the transmission it self.
Internal wear inside of the transmission can also cause harsh shifting. I my case I had 2-3 harsh shifting and I put in some Lucas transmission sealer/conditioner when I did the ATF/Filter change. This helped about 85%.

Brian Carlton · #3 08-31-2008, 11:02 AM

The "thingy" is a temperature vacuum switch for the EGR and you can ignore it.

However, one of the three lines that lead into the black plug on the black box is the supply vacuum. You should pull this line and put a short piece of hose on the line and then plug the line. Your transmission issues are likely caused by some leaks in the switches in the black box..........and you're not using the switches anyway because you've got no vacuum to the EGR.

Also, for future posts, kindly post the year and model of the vehicle. I've made the assumption from the photos that it's the '82 in your sig. If this is not the situation, none of my advice applies.

LuckyEddie · #4 08-31-2008, 11:07 AM

It is a thermo vacuum switch and it should be connected to the EGR valve. It delay es the EGR function till the engine comes up to temperature. I block my EGR valve and the vacuum switches on top of the valve cover. After all these years the valves leak. Block the plastic line in the Y connector that is uppermost at the injection pump, the lower Y connector is just a vent and it goes in under the dash.

Hope this helps
Robert

cewyattjr · #5 08-31-2008, 11:08 AM

Sorry, yes, 82 MB W123. I think I see what you mean, Brian... that vac line in the upper right hand corner of the black plug is just "hanging out in the wind" so to speak, right?

Brian Carlton · #6 08-31-2008, 11:13 AM

Quote:

Originally Posted by cewyattjr

Sorry, yes, 82 MB W123. I think I see what you mean, Brian... that vac line in the upper right hand corner of the black plug is just "hanging out in the wind" so to speak, right?

Only one of the three lines matters. I can't remember which one.

Start the engine. Pull all the vacuum lines from the plug. Feel each one for suction (vacuum). Only one of them will have it. Add a short piece of hose, if necessary, and plug that line. The others are irrelevant.

JHZR2 · #7 10-31-2009, 10:48 PM

So let me get this straight...

The 2/3 valves which connect on the top of the valve cover have three lines. The lines are vacuum, vent (open to atmosphere) and vacuum to the EGR, right?

The 2/3 "switchover" valves take constant engine vacuum, and either allow it to be presented to the thermo valve and ultimately the EGR for actuation, or else force it to vent to the atmosphere by a leak.

Now, I can understand the route for vacuum via this diagram, on post 31:
EGR Delete/Remove

I can see that vacuum comes in and goes to the EGR, but just to be sure Im accurate, there is also an "atmospheric" vent line which connects to other vents via some lines connected to the IP? So the IP gets some vacuum and has a line which is open to the atmosphere?

It seems that all "vent" lines share a common open to the atmosphere final line. Is that correct?

Thanks!

Brian Carlton · #8 11-01-2009, 07:59 PM

Quote:

Originally Posted by JHZR2

So let me get this straight...

The 2/3 valves which connect on the top of the valve cover have three lines. The lines are vacuum, vent (open to atmosphere) and vacuum to the EGR, right?

The 2/3 "switchover" valves take constant engine vacuum, and either allow it to be presented to the thermo valve and ultimately the EGR for actuation, or else force it to vent to the atmosphere by a leak.

Now, I can understand the route for vacuum via this diagram, on post 31:
EGR Delete/Remove

I can see that vacuum comes in and goes to the EGR, but just to be sure Im accurate, there is also an "atmospheric" vent line which connects to other vents via some lines connected to the IP? So the IP gets some vacuum and has a line which is open to the atmosphere?

It seems that all "vent" lines share a common open to the atmosphere final line. Is that correct?

Thanks!

Are you asking general questions regarding a 617 turbo.......or are you asking questions about one of the vehicles in your signature?

The answers depend on the vehicle.

tangofox007 · #9 11-01-2009, 08:16 PM

Quote:

Originally Posted by JHZR2

The 2/3 "switchover" valves take constant engine vacuum, and either allow it to be presented to the thermo valve and ultimately the EGR for actuation, or else force it to vent to the atmosphere by a leak.

Now, I can understand the route for vacuum via this diagram, on post 31:
EGR Delete/Remove

I can see that vacuum comes in and goes to the EGR, but just to be sure Im accurate, there is also an "atmospheric" vent line which connects to other vents via some lines connected to the IP? So the IP gets some vacuum and has a line which is open to the atmosphere?

It seems that all "vent" lines share a common open to the atmosphere final line. Is that correct?

There are three options for vacuum routing to the EGR valve. At idle, vacuum to the valve is "blocked." Above idle and below WOT, vacuum is routed to actuate the EGR valve (subject to the thermal switch.) At WOT, the vacuum routed to the EGR valve is vented to prevent EGR actuation.

JHZR2 · #10 11-01-2009, 07:52 PM

bump

JHZR2 · #11 11-01-2009, 08:03 PM

Sorry, 617.952 would be the engine in question. I assume it is similar for a federal OM616?

Brian Carlton · #12 11-01-2009, 08:21 PM

Quote:

Originally Posted by JHZR2

Sorry, 617.952 would be the engine in question. I assume it is similar for a federal OM616?

As TF mentioned above for the 617.952. The 616 is not the same. That valve will operate the modulator on many 616 versions and it cannot be disconnected. This would typically be engines without the Bowden cable.

JHZR2 · #13 11-01-2009, 08:22 PM

So it is "vented", i.e. sucking in atmospheric air then...

I noted it shares the ultimate vent tube with some other things coming off the IP, is that accurate?