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Old 09-09-1999, 02:18 PM
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Join Date: Jul 1999
Posts: 239
Is the vaccuum control valve on the injector pump a regular replacement item ?
Can a defective unit be a source of many strange symptoms such as rough shifting and sluggish acceleration ?
It looks like a white plastic piece that could get clogged or weaken over time after high heat and vibration.

Is the EGR valve common to all diesels or was this intalled in only certain models ?
Wondering if this should be replaced or serviced periodically.


Old 09-09-1999, 03:22 PM
Posts: n/a
Hi again... :^)

I haven't heard that the vacuum valve is a regular replacement item. My car was shifting very roughly and it turned out to be vacuum leaks and misrouting of vacuum lines. Has your car always been this way?

The EGR valve is not a regular replacement item but should be checked periodically. There is a hole on the top of it through which you can see the plunger go up and down if you pull on the cruise control arm. I use a flashlight to see better. Besides, that thing is really expensive...

Hoping this helps.


1982 300D -

Old 09-09-1999, 03:45 PM
Posts: n/a

I know of one very M-B knowledgeable individual who recommends that the vacuum modulator valve on top of a diesel's injection pump be replaced around 120,000 miles. I have replaced the one on my '83 300CD-T (at approximately 220,000 miles) and did so after following the testing procedure for this component as documented in the 617.952 shop engine manual. I consider it an expensive part at approximately US $120.00.

As far as the EGR valve is concerned, the one on my '83 did eventually fail (at about 200,000 miles) and I did replace it. Very expensive, around US $400.00. Like the vacuum modulator valve, I think it is best to diagnose the component before replacing to avoid unnecessary expense and work.

Good luck-

Old 09-10-1999, 10:53 PM
Posts: n/a
The white vacuum control valve atop the injection pump bleeds off the vacuum that controls the transmission modulator valve. They do wear out from time to time, or get clogged. The adjustment of this valve plus the bowden cable, plus all of linkages work together to simulate engine vacuum that the diesel does not have. Everything works together or it just doesn't shift right.

Old 09-13-1999, 08:39 AM
Posts: n/a
Silly question: what is the bowden cable, where is it and how is all that adjusted?

Third one could be a long answer, I'd take the first two... :^)


1982 300D -

Old 09-13-1999, 09:46 PM
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Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
The bowden cable is the cable that is attached to the throttle linkage on top of the valve cover. It is used to control the length of the shifts in correlation with the modulator vacuum.

1987 16V

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