New to mercedes. Just purchased my first, a 87 300SDL. I hope someone can help me with a vacuum leak at the plastic valve that operates the EGR valve. If I use my had vacuum pump I can hear air entering the top of the plastic valve. I can operate and stop the leak by manually applying ground to the electrical connector. Per my info, this missing ground should come from pin 7 of the EDS unit in the passenger compartment. I've checked at this point with engine running and the wire is good but there is no ground?? Anyone know what might inhibit the ground? Based on what I've read, I plan to remove the EGR, but am concerned that there may be a problem that I may be overlooking.... Also I've got a shutoff problem that I figured was part of the above issue. However, I tested my shutoff valve directly with a vacuum device and found I could shut it down if I pumped it briskly, but once shutdown the valve will not hold a vacuum. Is that normal or do I have a faulty shutoff valve?
Thanks - nat

if you have trouble shutting down then you have a vac leak. As you said the plastic valve that operates the EGR. Plug the line and see if you can shut your car down. if you can then thats your problem

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hum.....
1987 300TD 311,000M Stolen. Presumed destroyed

I do not think the shut off holds a vacuum. It has to return to the run position for the next start.

No need to waste time with the EGR and ARV systems. The two vacuum lines going to them can be removed and the tee at the vacuum pump plugged where they were connected. The air meter box can be removed and replaced with a adjustable metal duct pipe.

EGR does not operate continuously so you might not get a ground signal from the EDS module under the condition you're testing.

The shutoff lever should stay down for days after you turn the key to OFF. It should pop back to vertical when you turn the key to glow. If I follow your description, you say you can stop the engine with a vacuum pump but the actuator doesn't hold a vacuum. It should hold at least 15"Hg.

Although EGR and engine shutoff draw vacuum from the same pump, there are separate lines feeding each system. EGR draws vacuum from the circuit that serves ARV, transmission and ACC. Engine shutoff draws from the big line to the brake booster. A healthy vacuum pump will suck the chrome off a trailer hitch so a loose EGR line will not make a much difference. At most you might notice just slightly stiffer shifts.

Sixto
87 300D

Thanks for the helpful information. Using a vacuum pump, my shut-off valve doesn't hold any vaccuum. With the shut-off valve disconnected, I measure 23gh on the line. The shut off problem seemed to get progressively worse over a couple of days. I guess that was the symtom of a dying diaphram. Ordered a new valve this evening. Hope that fixes me up. My transmission was shifting a hard and hopefully pluging off the EGR and associated hardware will make a difference. Just curious, can anyone shed light on what the vacuum connection on the botttom of the 5 way connnector (the one that fed the EGR) does? My drawing says "filter"???

Thanks Again!

It's the line that goes to the pump. I guess the filter is there so the pump doesn't ingest something it ought not to, and it ought to ingest only air.

Sixto
87 300D

Oldblue85!

Exact same problem with mine. Tell me, did the new shutoff valve do the trick? Need to fix, driving me crazy.

Thanks,
James

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1986 300SDL ~300,000 mi.
1989 560SEL ~175,000 mi.
2011 F-150 ~37,000 mi.
1953 M38A1