pa-hawk

I am not sure if this is the right place to be asking this question. This is my first post and not too familiar with the site layout yet. My question is this, I have a 2007 C280 4Matic and when I changed oil the other day and removed the cover to access the oil filter, I noticed a hose that goes from the front of the air filter to what looks like a pump (although it is not driven by the belt) was not hooked to the air filter. I had it to the dealer for some service 2400 miles ago and they did not hook it back up. What device is the hose hooked to and is there any chance any damage was done by it being off for that long? I am still trying to find out why my fuel milage had dropped from 26 to 24 at best. Through last winter and through this summer I was usually getting right at 26 for what is mostly highway driving. Thanks in advance for any help. I would like to know about the hose before I call the dealer. By the way, my milage dropped before I had it in for service and has not gone up even after I re-connected the hose. The milage drop seems to coincide with putting new tires on. I went with Michelin Primacy MXV4. From what the tire people have been telling me it is normal to lose fuel milage with new tires but usually only one at the most and of course you will recoup that as the tread wears down.

pcy

I think you are talking about the hose that connects the secondary air pump. Please take a pic and post here.

Mileage variation may have lot to do with [many factors, including] tires, tire pressure, driving style, etc.

pcy

Is this the hose you are referring to?
If so, that is the hose that connects the secondary air pump to the air filter assembly. That pump is run during the first couple of minutes of starting the car (when the engine is cold).

pa-hawk

Thanks for the reply, yes it appears to be what I am referring to. Mine actually connects to a nipple on the front of the air cleaner housing, not the way the one in the picture is set up. What runs it and what is it’s' purpose? Is it vacuum driven by chance? As to the gas mileage, I did add two psi front and rear to see if that helps. My driving habits haven't changed so that is out. The drop did happen when I had the new tires installed so I guess I'll just wait and see if it creeps back up as they wear. Thanks again for the info.

pa-hawk

Sorry, I just looked at the picture again and the hose that (appears) to be connected to something under the air cleaner is not. My mistake, I didn't look close enough.

pcy

As you realized, that hose is not connected to anything [in the picture]. That hose connects to the air filter housing. That hose is there to direct the [filtered] air from the air filter housing in to the secondary pump. Without that hose being connected to the air filter housing, the air pump is getting the unfiltered air into that air pump. Just reconnect it, and you are good to go.