class280

Hi all, Im new here so please forgive me if this question was asked already. I have a 1999 C280 and Im hearing a high pitched hum. Found the noise by the rear passenger side by gas tank. I don't have a repair manual so not sure if its the fuel Pump Or bad filter. Car starts and runs fine. Any help would be great.

ptcruiser

It is probably the pump that activates the door locks/trunk lock etc.
If you remove the trunk liner on the gas tank side (there are 3, one on the right, one on the left, and also the main trunk floor mat). It's the one on the gas tank side. You have to remove some plastic clips to remove it.
Once it's out, the pump is there, and has several vacuum lines attached.
If it runs continually, you have a problem. If only for 5 or 10 seconds, then your ok.

class280

Thanks for your reply ptcruiser.
I will check it out and post back. I do know that the noise is constantly on when the car is on. Somedays it's loud others its not as loud. The car runs fine except for that noise.

ptcruiser

You probably have a vacuum leak.
The pump builds up a reservoir of air to activate the door locks etc.
If there is a leak, the pump will keep running.
It's tough to pin point the actual location as there are several vacuum lines running to different locations. You can remove each line independently from the pump motor, and block off the nipple on the motor. When the line that has the leak is disconnected, and blocked off. the pump should stop running.
If it is running continually, the pump motor will eventually burn out.
To avoid that, disconnect the pump wire electrical connection, and use your key to open the door.
To check all the lines should take about 30 minutes, and be very CAREFUL removing the connecters from the pump motor, as the vacuum lines become brittle with age.
You can put a tiny drop of oil where the rubber nipple connects to the pump motor and just LIGHTLY twist it side to side to remove it.
Best of luck.

class280

I will give it a go. Thank you very much for your advice. I will post my progress.

ptcruiser

If you have any questions as you proceed, just drop me an email
bfwilson2000@gmail.com

class280

I will. I have to see what tools are needed. Tough keeping stuff in an apartment. Lol

ptcruiser

To do the job, there are no special tools required.
You have to remove the plastic trim that you can see when you open the trunk. There are several small rectangular clips, and in the middle of the clips is an expansion piece. Just pop out the expansion pieces with a small screwdriver, and remove the trim piece, then remove the side trunk liner to see the pump. Be careful removing the clips, as they have a habit of popping out and disappearing. Be sure to put them in a baggie.

class280

Ok, went to do the job and my engine started smoking. Turned out to be a broken hose for the engine coolant. That hose was a son of a gun, because it is one piece with multiple connectors. Well, got it on and now gonna tackle that pump noise this weekend.

ptcruiser

And now the fun begins :-)
Keep me posted, and if you find the leak, let me know if I can be of any further help.
As I live out of the country, I can just send it to the Mercedes shop (not the dealer) and things are so inexpensive, it hardly warrants getting my hands dirty.
I just had it in the shop as I had a check engine light, and for a full analysis on a Mercedes scope, remove and clean the throttle body, replace a crankcase ventilator hose (including the part), replace the air filter, and reset the computer. Total $85.00.

class280

Okay, here is the deal.
Took panel off from inside trunk. Nothing to signify sound. Then, checked underneath the car, saw a small drip. It was gas. Turns out the fuel pump threading was destroyed. Then, the previous person who worked on the car put the wrong clamps on the fuel hoses causing them to puncture.

So, I cannot do any work at my apartment complex so I had to take the car in to a shop. Fortunately for me, I've been doing some research a while back and found a repair shop that specializes in Mercedes.

Long story short and $707.07 later, the noise and leak along with bad gas mileage was solved. I have the breakdown and price if anyone wants to know.
I also got a list of other things that will need to be done. I can post it if anyone wants to know.

ptcruiser

$707.00 big bucks...........
I feel for you, as that is a lot of money.
I hope the car is worth it in the long run.
Tough deal they won't let you work in the apartment parking area.

class280

It hurts but I really like this car. The other stuff is preventative maintainance including two leaking gaskets.

Ahhh! The price of luxury!

taz069

Please post the break down of the shop bill please!!!!! Mine is doing some buzzing also. Did they replace to sending units in the tanks???? Got my pump and filter changed and the sound persists!! Thanks

class280

Hey taz069,

Sorry to hear that you are going through this but hopefully I can help. First, my mechanic showed me where the buzz was coming from. It was actually the fuel filter and the brand name is MANN. He said that this brand is notorious for causing these problems on majority of Mercedes.

Also keep in mind that I had a fuel leak due to the used car dealer incompetent mechanics destroying the threading and putting clamps with teeth on the rubber hoses.

With that said here is the bill breakdown.

Labor Mechanical $126.50

Part# 0004706394 Fuel Pump $383.05

Fuel Hose - 2 pieces $50.00

Hose Clamps - 6 pieces $24.00

Part# 0024773101 Fuel Filter With Pressure Regulator $66.00

Plus $5.00 Hazmat and another $5.00 for supplies and tax of $47.52

Now again, I had to get a new fuel pump but the actual noise was coming from the fuel filter. If this is your problem, consider getting an OEM fuel filter.

Hope this helps.

taz069

Understood Class280Thanks!!!! Will cross that bridge soon, having another issue now. The timing on my lil c280 is going from -7.6 @ 576rpm to -15.1 @ 704rpm. Have replace the cam position sensor and problem persists. After 1000 rpm runs great! Looking for vacum leaks and gonna get some dif gas possible got a bad tank full. Thanks again.

class280

No problem taz069.

After some cheap or low grade gas helped to ruin my previous car (93 Maxima) Now I only use Chevron Premium grade on this car. I checked with majority of mechanics and they said the cheaper gas doesn't have a lot of cleaning agents in it. That's why they sell those fuel cleaning additives. They recommended Chevron, Shell and Mobil, in that order.

Good Luck!

taz069

Bit the bullet on the question on my timing. When online and paid 45$ long story short my timing was 1 tooth off. I didn't realize the intake cam adjuster had to be rotated completly clockwise upon reinstall. Yeah my dowel pins lined up for timing when i did tdc. It runs great now.