S211 Air Suspension Compressor noise

[Paulo1967]

Today I became aware for the first time of a buzzing noise from the rear of my 08 S211. It seems to originate from the rear left, which leads me to assume it is the air suspension compressor. It runs noisily from when I switch the ignition on, until the engine is switched off. The car is not sitting low, and seems to ride normally. Anybody have any idea what the issue could indicate?
Thanks.

 

[zipdip]

Well it is strange that you say that the noise from the compressor is happening all the time,whats suppose to happen is that when you start the car it might kick in to top up the air tank,then it should stop until some air is used out of the tank,I suggest that you might have a leak on the system.

 

[Paulo1967]

Well it is strange that you say that the noise from the compressor is happening all the time,whats suppose to happen is that when you start the car it might kick in to top up the air tank,then it should stop until some air is used out of the tank,I suggest that you might have a leak on the system.

Thanks for the reply. I just tried it again on the drive, switched on the ignition but not the engine. As you say, it ran for maybe 30-40 seconds then stopped, but I don’t recall it being noisy before.
I’ll monitor this and see if it persists - earlier when driving it was buzzing all the time for about 30 minutes.

 

[mersum1es]

There is a 30 seconds time limit when compressor is switched off in safety reason (not burning electric motor), usally such behavior is due to leak somewhere, or too worn compressor unit (pump cannot reach required pressure). Even pressure is not high enough, it can still be enough to maintain car height. Reservoir pressure is around 15bar when struts need ~under 5 bar to keep car in balance,

 

[zipdip]

If you go to a MB indy they can run a test scan on the compressor they empty the air tank and then start the compressor it has a set time to fill the tank,that shows if the compressor is worn and needs replacing,but that fault nearly always puts a fault up on the dash,because you say the car is at the right level,my bet is that there is a leak between the compressor and the tank,it could just be a connection leaking,but the longer you leave it will wear out the compressor.

 

[Wearsthefoxhat]

The compressor for the Airmatic on my S211 is in front of the passenger side front wheel behind the bumper…

 

[zipdip]

The compressor for the Airmatic on my S211 is in front of the passenger side front wheel behind the bumper…

The fact that the op said the noise was from the rear,I assumed he has a estate S211.

 

[Wearsthefoxhat]

Fuel pump perhaps..

 

[Paulo1967]

There is a 30 seconds time limit when compressor is switched off in safety reason (not burning electric motor), usally such behavior is due to leak somewhere, or too worn compressor unit (pump cannot reach required pressure). Even pressure is not high enough, it can still be enough to maintain car height. Reservoir pressure is around 15bar when struts need ~under 5 bar to keep car in balance,

Thanks. Reading the replies I am beginning to think a leak in the system or a failing compressor is likely. It obviously tops up the tank when the ignition is turned on,

 

[Paulo1967]

Thanks everyone for your advice. I will get it booked in to be looked at, hopefully it’s just a connection, but who knows what world of pain I could be facing

 

[zipdip]

Thanks everyone for your advice. I will get it booked in to be looked at, hopefully it’s just a connection, but who knows what world of pain I could be facing

Well at least your car is level and showing no sign of dropping,if it is a leak between the compressor and the tank then it will only be a small pipe fitting to mend it,as always share your pain with us we like to hear what you did to fix this fault.

 

[Paulo1967]

Well at least your car is level and showing no sign of dropping,if it is a leak between the compressor and the tank then it will only be a small pipe fitting to mend it,as always share your pain with us we like to hear what you did to fix this fault.

I’ll let you know. Booked in for visual inspection Friday.

 

[Paulo1967]

An update on this for those of you are interested.
I took the car to my local specialist on Friday. It is indeed the fuel pump unit in the tank that is playing up.
Interestingly there is no detriment to the running of the engine, suggesting that the fuel pump is still functioning correctly at the moment.
We replaced the fuel filter just in case, but it is clearly the pump that is at fault.
It runs very loud and the noise is continuous, and obviously from the rear of the car.

In one sense I am greatly relieved as the air suspension is in perfect working order, however fuel pumps are not cheap either it seems.

I’ve ordered the correct part and it should be fitted next week, which should solve this problem.

To be fair, I have had the car over three years now and this is the only problem I have had requiring me to spend money, over and above servicing and tyres.

So mystery solved!

 

[AntMB]

Air suspension, the triggers broom of these cars! But glad you got it sorted.

 

[zipdip]

Pleased you found the fault and are getting it fixed.

 

[Wearsthefoxhat]

Thank you for taking the time to report back….

 

[Paulo1967]

For anybody who is interested, this adventure is (touch wood) now concluded.
the price for the MB genuine fuel pump part came in at £580 inc vat, exclusive of Labour to fit it. This caused a sharp intake of breath. So I went onto eBay and picked up the same part number but manufactured by Delphi for £160. It finally arrived yesterday, just in the nick of time for the car to go in this morning for the work to be done. Needless to say, the drive to the garage, which takes about 30 minutes, was rather tense as I was willing the old pump to keep going until I arrived!
The pump is now replaced, and I am hopeful that there won’t be any more strange noises for quite some time!!!