WUR Vacuum lines - Mercedes-Benz Forum
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post #1 of 16 (permalink) Old 08-11-2019, 05:29 AM Thread Starter
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Date registered: Apr 2019
Vehicle: 1978 C107 280
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Hi
Quick question about the vacuum lines coming from the WUR, the car is not running right at start up so I am hoping it is this. One of the vacuum lines is disconnected and I cannot for the life of me work out where it should be connected ( does not help that the WUR is horribly placed)

My car is a 78 Euro 280, the vin being WDB10702222005099.

In the attached diagram it is the line labelled 794 and is disconnected at the Y junction. The problem is I think this diagram is incorrect for my model, my car has no holes in the AAV to attach a vacuum. If anyone has access to the EPC would be amazing
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post #2 of 16 (permalink) Old 08-11-2019, 06:08 AM
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My AAV doesn't have any direct vacuum line connections, the lines connect to the rubber hose either side of the AAV.

This is my 450 so may not be directly applicable but may help with your search, I have highlighted the WUR connections to either side of the AAV.

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post #3 of 16 (permalink) Old 08-11-2019, 06:16 AM Thread Starter
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Okay I think I may have located it, will try and reconnect then report back
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post #4 of 16 (permalink) Old 08-11-2019, 07:47 AM
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FYI. The posted diagram is the same as the EPC. There are a few on line versions of the EPC. The first is what I remember the new EPC format looked like. https://nemigaparts.com/cat_spares/epc/mercedes/
https://mercedes.7zap.com/en/eu/fg/car/
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post #5 of 16 (permalink) Old 08-11-2019, 12:55 PM Thread Starter
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Okay update, found the place for the vacuum line and plugged it in. Car starts a lot easier but has been idling very high though. I assume this is because I had previously adjusted the idle to compensate the rough cold running, I have turn it down and seems to better now.

Weird thing is that the vacuum hoses are quite different to that diagram, completely missing one part.

Thanks for your help, will update after a long trip!
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post #6 of 16 (permalink) Old 08-11-2019, 01:20 PM
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That diagram is for several model years so not all parts will apply.
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post #7 of 16 (permalink) Old 08-12-2019, 09:07 AM
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Race Diagnostics,I'm going to hi jack here for a moment. In your picture, the forward hose leading to AAV has two lines connected. One to the WUR, where does the other one terminate??? Thanks
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post #8 of 16 (permalink) Old 08-12-2019, 09:22 AM
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No problem, it goes to the lower port on the advance/retard diaphragm on the distributor.

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post #9 of 16 (permalink) Old 08-12-2019, 09:56 AM
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Thanks,very interesting. I'll have to check my distributor.Right now that port on the hose is plugged??? Okay,checked mine and that line from the lower point on the distributor goes all the way over to the dual vacuum connection next to the coolant overflow jug. I also have a "79, but of course USA model so may be different. I have been trying to sort out all the vacuum connections since I got this car last year. It had the wrong WUR on it and everything was bastardized.I've got it running a lot better but still not perfect. Thanks for your info, I may try moving a few lines around and see how it goes. Thanks..
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post #10 of 16 (permalink) Old 08-12-2019, 10:21 AM
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That means that you have a car with AC, when the AC clutch activates at idle it can stall the engine so the timing is either advanced or retarded a bit to stop this happening.

My car originally had AC but I swapped the engine for one from a non AC car.

On the old engine the tube went from the distributor to here, the AC switchover valve.



But the striped tube wasn't connected to anything, I changed the engine before I needed to work out where it should have gone to.

Last edited by RaceDiagnostics; 08-12-2019 at 11:05 AM.
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