mecca281

Fellas,

For a while now (about a yr) I have been getting a faint rattle/flapping noise at right below 1000rpm. Sometimes it's really low, sometimes is very noticeable.

Sitting in the drivers seat it seems to be coming from the rear passenger side. I don't think it's the exhaust rattling...which is on the other side

When idling close to 500rpm it goes away.

Any ideas?

Thanks in advance.

Rudeney

Do you hear it only when rolling or also when stopped? The fuel pump can makes some tapping noises when you decelerate and it seems to be louder in the cabriolet than the coupe models, and it is normal. If it's only when rolling, then it could be some of the underbody sound insulation running against the driveshaft. I had this on the C240 and chased it for months until I found it at the very rear of the driveshaft.

mecca281

I hear it almost discretely when I am right below 1000rpm, so since that is a little high for an idle it usually happens when I am decelerating. Once in a while I idle a little higher and hear it. It also seems to vary in decibels (louder) rather than frequency. It's always the same rattle/flapping.

mecca281

Hmm... After a little investigation I noticed a ticking/vibration coming from the main brake fluid lines in my hood, close to the resevoir. The line seems like it's pulsing and that may be travelling back towards the rear passenger break... Just another thought (I'm still lost)

Anyways I wonder if it is brake line related would it only happen at right below 1000rpm and even when idle"

Glyn M Ruck

Are you sure that it is not the EECS (Evapourative Emissions Control System) purge valve. They can be noisy & get noisier as they age. Replacement is all that will shut them up.

mecca281

That absolutely is the culprit in the engine compartment. I'll plan to replace it soon.
Do you see that being a problem only during low speeds and idles?

Also what are some symptoms of a failing eecs valve?

Glyn M Ruck

Yes ~ only at low speeds and idle. As revs increase it shuts up or becomes less noticeable.

They seldom actually fail. What starts as a flutter becomes a loud tick but they still operate as designed. Seldom any symptoms at all.

mecca281

Could this in any way cause slight hesitation at that rpm at low speeds?
I have this small jerk once in a while if I rev up (2000rpm) quickly, let off the gas and rev up again, the transition is seldom smooth..
The thing is I live in houston, so pedal footsie is a requirement, unless u want to hit the guy in front of you who just randomly came to a stop. Lol

Glyn M Ruck

If the purge valve is leaking it will have minor effects on mixture. Sometimes a little too rich & sometimes a little too lean.

If you accelerate hard & then jam on the brakes again quickly & the transmission jerks slightly it is usually that you are catching out the torque converter clutch as it is trying to lock up.

mecca281

So... I have disconnected my purge valve and I sprayed CRC electrical cleaner on the contacts, can I also use it to clean inside the valve? If not what can I use and how do I clean it? I've read that cleaning it is the first step before replacement.
Thanks for all your help!

Glyn M Ruck

Electrical cleaner will clean inside the valve pretty well. Cleaning is not a bad idea but I have never found it to silence a noisy purge valve though. In fairness most people only complain when it starts to tick loudly so give it a try.

mecca281

So.. After cleaning the valve, I still hear clicking from the valve, I finally decided to look under the seat where the noise seemed to be originating, and voila!! It's my fuel pump filter assembly.

All sorts of wierd things seem to be going on, first there's all this sticky brown stuff everywhere under the seat cushion (cleaned up before snapping the picture DOH!") 2nd the pump is definitely making the noise, 3rd there is air coming out of the pump area after I removed the panel covering under the seat cushion as seen in picture. What is this air, and the brown stuff..

Plus how in the world do I get the pump out it seems sealed...

Glyn M Ruck

There is supposed to be a metal cover plate over each fuel level sensor. Sounds like fuel has leaked onto some anti drumming spray. You have 2 level sensors with the fuel pump included in one of them.

There are 2 sealing systems to undo the sender units. Older ones have a threaded knurled ring that you unscrew like the metal ring on a glass jar. Newer cars have a large metal clamp that undoes like a hose clamp.

The air is outside air. The saddle tanks hang under the car. See Wiki for diagrams etc.

Rudeney

The tapping noise from the fuel pump is actually normal in the cabriolet. The weak seal rings can make it louder, but even with new ones it will still make some noise.

mecca281

Normal?? Do you mean it happens a lot, lol...I'm not sure that makes it normal behavior.
Anyways I took it to my Indy and he definitely says it's a concern. He says "that's a wierd sound for a fuel pump to make"

I'm also noticing a drop in performance. My Indy had done some work on the fuel reservoir before.. Every time I filled up at the gas station I would smell gas until the level went down a little bit.(quarter tank)

He told me there was something broken and that it was usually due to pressure flux in the gas tank.
He "fixed" it and the smell of gas went away after filling up.. Now I'm getting pump issues from the same area about a year later.

Glyn M Ruck

He probably replaced one of the rubber seals.

Check your fuel pressure at the Schrader valve on the front fuel rail that connects the injectors. s/b > 3.8 bar or 55 psi.

Fuel pump should make a low buzzing noise while running. It is sometimes audible if you really listen for it.

mecca281

Here is video of the sound. Turn up speakers to hear. I don't think this is anyway normal.

Glyn M Ruck

No. That is ridiculous. I have never heard a Benz pump make that noise.

Glyn M Ruck

This is the purge system & fuel system. This is for M112 V6. M272 is the same. The only thing that changed on newer cars was that the fuel filter moved from outside the tank to inside the LHS sender unit.

I almost wonder whether the purge system is transmitting that noise to the rear. These cars use a rotary fuel pump not a diaphragm unit.

mecca281

thanks for the diagram!

Hmm... so from looking at this, it seems like the fuel pump is actually on the rear driver side?? Interesting, i remember opening that panel once and only seeing the parking brake tensioner, i guess the pump is below?

Also, the sound and vibration sounds like its definitely coming from the rear passenger... what is housed there?

ps. in response to your statement, if it was the purge valve i think it would be constant with the vibration in the engine compartment... this seems to be doing its own thing, and i think my indy agrees.

question: what components of this system would i be able to maintain in my car since the pump and filter are intank? the activated charcoal canister?

Glyn M Ruck

You should have 3 hatches under the seat. A square one at center with the parking brake adjuster & two round ones on either side each with a fuel level sender underneath it. One sender contains the fuel pump (and on newer cars the filter).

There is nothing you can really maintain other than the fuel filter. Senders have to be replaced as a whole including fuel pump if necessary. Carbon canister requires no maintenance.

The US rear passenger side should just have a fuel level sensor but we have seen cars on the W203 forum with the sensors & pump reversed.

Disconnect the purge valve & see if it has any effect on the noise at the rear. Then we have the purge system out of the equation.

You could also have a piece of Cat honeycomb that has broken off & is stuck in the silencer.

mecca281

Hey thanks for all your help! I was worried about disconnecting the valve and driving with it because I wasn't sure if it would cause damage.

I tried it anyways as you suggested and the sound went away, I plugged it back in and it returned, so it seems it is the valve.

Does this valve have an N/O or N/C fail position? I'm assume N/O since it's a purge? Also how long can I drive with it unplugged.

Glyn M Ruck

I would not drive too far with it unplugged. Rather reconnect it until you decide what to do about it. If you overfill the tank & saturate the carbon canister you need it to bleed raw fuel into the inlet manifold in a controlled fashion.

I find it interesting that the purge circuit is transmitting the noise. I wonder if all is in order. There is no such noise on a Coupe & I don't understand why the Cab should be any different but NVH issues can be elusive.

I guess you can see what a new purge valve achieves.

I don't know whether the purge valve typically fails open or closed.

Rudeney

I have heard this in many cars (W203, W209 and W211) - most every one I have driven. Like I said, it's more noticeable in the cabriolets. I believe the sound is a relief valve that clicks as pump pressure is equalized between the two tank halves. It's usually heard more often when slowing down and may last 10-20 seconds after returning to idle, then it stops. It should not make this sound constantly. It can usually only be heard when it's very quiet in the cabin - no radio or conversation, AC fan off, etc.

Glyn M Ruck

Never heard anything other than the typical pump buzz. On my C240 you could not even hear the pump buzz inside the car.

In the case of mecca's car I think we have proved its the EECS purge system that is making the noise. Nothing to do with the pump which is rotary.

I've had many car's seats out & opened up & running. None has made the noise in mecca's clip. Only fuel pump buzz.