Hi,

I have a 1995 C280 which was recently serviced. Before bringing it in, there was a recoccuring noise in the area of the right - rear passenger door or coming right from behind. My mechanic said it was the fuel line or pump and said he fixed and the noise was normal (its still there) and I don't think its normal, and passengers in the rear complain about it because it sound like a pump filling up over and over again. Just a little info about it - the car started doing it about 75,000 miles, and so did my 94 C220 and it still does it. It will make the noise in Park, Drive, Reverse for about 5-10 mintues, and after driving it eventaully stops. also, when the battery is turned on only, it will make the noise. Please help with this issue - is something that can be fixed or is the aging of the car.

Thanks,
Troy

Sounds like the central locking pump is running. MB uses this pump for many duties, including manifold assist. IF there is a vacuum leak in A/C system then this pump will help supply vacuum so that ducts can open & close. The pump is in the trunk on the rt side behind the carpet. LIsten & see if its running. The reason it shuts off after 5-10 minutes is thermal overload protection. NOT good.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

I have the problem in the same area. But a little bit more serious.
One c280 came to me with complaint that central locking isnt working. Pump motor burned- so i replaced it with a different one (motor not the whole PSE). Everything was working fine ntil car left garage. The vacuum pump started working constantly when the throttle was apllied. Here is the interesting part - the more throttle- the faster pump runs. I checked the line from the pump up to vacuum valve block for leaks- none found. I unplugged all the lines from the vac valve block and tested them- everythig fine.
So i concluded that the problem is in vacuum valve block- got the new one- still no change. I plugged the vacuum line from the intake manifold- no problem. What components are there between the vacuum valve block and the pump vacuum line ?
Should there be a one way valve somewhere? As far as i understand the vacuum valve block should not let the vacuum pump to suck the air from manifold, but in this case it does.
Or is the problem in the PSE? It shuts down when there is sufficient vacuum in the line, so may it be going nuts?
Central lock is workig fine.
So, shortly speaking there is a twoway connection between the PSE and the manifold.

Thanks for bearing with me, i am out of ideas and cant find any info on this MVA-SRU system.

I had this same noise in my boot (1994 C180 Euro) last year . It sounded like a buzzing sound every 1 or 2 seconds for about 15 minutes from start of every journey. The sound goes away after a while. It comes back after I restart the car for another journey. Very irritating sound for rear passengers. My indie took down the whole dash and found 2 airflow actuators had torn rubber diaphrams which therefore couldn't hold vacuum. These were replaced and the noise stopped except for just 1 buzz when the engine is switched on. The main problem the leak caused was the rearheadrests refused to come down when the button was depressed with the engine running. Not enough vacuum. This year, recently, my centre a/c vents are working off and on and I think there are more problems with the vacuum system. Can anyone help out on this? Most of the time no or very little comes out from the centre vents, sometimes it works properly for a few kilos then stops blowing completely. The side vents work properly all the time.

The problem in your case probabliy is either in the nozzle's vacuum actuator or in the vacuum line to it. You could get to the nozzle and check if the diaphragm is ok. If it is fine then it is kinda hard to find the leak in the line