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Old 02-16-2001, 03:23 PM
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I regularly inspect my '76 230 (4 cyl gas) engine for anything odd, because my mechanic is really a VW specialist and I had him install my engine. I have found a hose coming from the bottom of the engine block (on the side of the coil and brake cylinder) and it seems to be plugged up with a bolt. I cant seem to find out what it's for as my Chilton's manual doesn't have a complete map of my particular engine.

Is anyone familiar with this 115.951 engine and what this hose could be for ? I'm wondering if it has to do with all the idling problems I've been having lately ?



1976 230.4 W115

P.S. The black hose is about 3/4" in diameter.
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Old 02-16-2001, 04:58 PM
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Join Date: Jul 2000
Location: Toronto, CANADA
Posts: 1,193
I have an idea, and this may be way off base as I have no knowledge of your model. On my 1986 420SEL I have the same set up as you. There is a secondary air pump under the alternator. It has two hoses going to it. One goes up to the air filter housing to get fresh air, the other goes from the pump to the engine block. I'm not tech expert, but I understand that this pumps fresh oyxgen into the exhaust gases to help them burn better in the cat converter. I am pretty sure your car has a cat. as most did from 73 or 74. The air pump is only susposed to work until the temp is up and the mixture has leaned it self out. I would suspect that this is supposed to go to your air pump. These air pumps are very expensive (1200 for my car). Maybe this pump failed in past and a previous owner could not or would not afford to fix it. So someone removed the air pump and since it was easier to plug up the hose going to the engine block than to plug up the hole in the engine block they did that.

Please remember that this is just an guess, but I think it is reasonable. Please get this confirmed before you do anything about it. If you do need an new air pump, I would recommend you search Benz recyclers. That's what I did and I got a great used one for 350 instead of a new one for 1200.

Good luck.
Jason Priest
1999 E430
1995 E420 - retired
1986 420SEL - retired
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Old 02-19-2001, 04:45 PM
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Thanks, I'll check it out. As I recall, there is nothing below my alternator, however, there is something that looks like it could be an air pump, beneath the power steering pump on the driver's side. There is a short hose going from it to what looks like a converter of some sort and then a small vacuum line coming out of it. Ill check and see if there is a receptacle for another hose or not. If not, I'll have my mechanic check it out for me.


1976 230.4
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Old 02-20-2001, 01:26 PM
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Ah hah ! I think I've found it !

As for the air pump, mine seems to be in O.K. shape, but what I did find is that my model 1976 230, is supposed to have a vacuum pump (located over top of the power steering pump) and mine seems to be missing or gone! This could be why I've been having all these idling problems since I bought the darn thing.

Thanks, for pointing me in the right direction !


1976 230.4 W115
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Old 02-22-2001, 11:39 AM
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Actually, false alarm, upon talking with my parts supplier, my model doesn't have a vacuum pump(only 1977 and later) so the search is still on.

I have since looked under the engine block and noticed that this hose comes out from the bottom of a converter of sorts that originates from the air pump and a hose runs from the air pump to this vacuum valve (or whatever it is) This hose then comes out of the bottom of this valve and is plugged up with a bolt.

Any other ideas as to what it's purpose is ?


1976 230.4 W115
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