c240classic

Hey folks,
I have noticed something odd lately when i park the car i hear knocking sound almost like someone is trapped inside the trunk, very audible. The suspension is sound and tight, checked the muffler hangers. I realized it only does that when my fuel tank is anywhere from 3/4 to 1/4 full. I thought that was coincidence and brushed away the thought but i went to the gas station 2 weeks ago and it took me 20 minutes to fill up my car. It puts like 1/2 a litre in and the neck back fills and shuts of the pump. Then the neck slowly drains itself and then i can put another 1/2 liter in and so on.
I thought maybe just the gas pump was bad but yesterday i filled up again at a different gas station and it did the exact same thing. Its almost like this thing that is in the fuel tank is close to the filler neck input and partially blocking it. The fuel level sensor works fine, what else is inside the tank? I have never heard of such a problem, am i imagining things. Can something come loose inside the tank? Can something break off inside the fuel refilling nozzle at the gas station and go inside my tank? Really confused on this. Please advise !

ctC230K

right, so that sloshing sound inside your fuel tank would be gas......... mine made that sound too. it's normal. unless you actually have a body in the trunk, in which case you should find your nearest patch of forest and dump it!

skittles

i think he has a bigger problem than what you think. 20mins go - stop - go - stop filling up is not normal. something is blocking something. i think..

c240classic

I guess the baffles are common problem, they come loose inside the gas tank and that seems like whats knocking and possibly blocking the nozzle. Anybody ever have their fuel tank replaced? i am guessing its not cheap.

LILBENZ230

I hear a knocking like someone is trapped in my trunk sometimes, too. But only when stopped at redlights, and only in wet conditions, and only sometimes. Very weird but my car has done this for a long time and nothing has ever come of it. So I'm not going to worry about it.

samaritrey

This thread is scaring me. i always go to the same gas station unless i am out visiting my mother. over say the last 4 fillups one time the pump shut off when it was full the other three have been stop and go every two seconds. the one that was fine was a gas station near my mom the other three where at the same station? so either my car is screwed up or the station needs to do some pump maintenance?

Carsy

1.I would try to feed a half inch piece of plastic garden hose down your filler pipe & see if you can feel any restriction & see whether it moves. eg baffles or kinked filler hose.

2.Does your fuelflap lock properly ?. Some idiot may have put an object down there.

3. Find a drawing of your fuel tank & see whether you can access a viewing hole or where the filler enters the tank.
Good luck.

c240classic

Filler hose is not kinked, you can take the rear passenger inner fender off and the hose is right there from the filler neck to the tank inlet. It is in good condition.
It is not a fuel sloshing sound, it is a clunking sound. The clunking happens when the fuel is sloshing. Makes me to believe that whatever it is, it is inside the tank.
I am going to dry feeding something down the filler neck and see how far down the resistance is. I have to make a 2400 kms drive and i am afraid i am going to be out of gas and not be able to put any in!
I do not have any dead bodies in the trunk, or living ones. I make sure i dispose of them in a timely fashion :P . Although the last ones did say that i will haunt you forever !!

Benzben

I wouldn't worry so much about that. I went to a gas station once where they had replaced the nozzle on the pump I tried to use. You could tell the metal (aluminum, I think) was brand new. I went to stick it in my car, and...CLUNK. The piping they used for the nozzle was too big. Just banged against the outside edges of the receptacle. There are a lot of gas stations being run by idiots.

Glyn M Ruck

You have 2 tanks & two floats. The noise is the floats. You most likely have a blocked tank breather.

c240classic

Glyn, you are a wealth of information! what does the float do ? Because my fuel level is reading fine! How do i access the tank to take the float out do i have to remove the seats and go through the trunk ?
Where is the tank breather ? How can i check if it is working!!?

samaritrey

You remove the rear seat to get access to the tanks. the float does fuel level.

c240classic

hmm then it cannot be the float.. because my fuel level is working fine!

what would prevent fuel from going in the tank?

bdgdl08

I think what he's saying is that the floats are making the noise, but not necessarily causing a problem. The shut-off for the gas pump relies on back pressure. If your breather is blocked, then it may be creating enough pressure to trigger the shut-off.

c240classic

Brilliant guys !! and stupidity on my part!

I think i have figured it out. This problem started happening after i took off my charcoal canister to check for leaks. I took apart the shut off valve to see if the oring was leaking like someone else had mentioned!
While i was trying to take the shut off valve apart, the whole thing, fell down and disassembled i put it back together to the best of my knowledge.
I must have put it together the wrong way. I am going to take it apart and see if i can put it back the right way. anybody have any input on whats the right way to put it, it has like a needle actuator and a rubber oring and solenoid and a few other odds and ends.

Glyn M Ruck

Aha! - You got it. The tank has a breather via the charcoal filter & if you look at the diagram of the tank system you will see the pipes - one from the top of each tank that connect together & then run up the side of the filler neck.

When you are putting gas in - air must come out. If air can't come out then gas backs up the filler tube & shuts off the pump nozzle. For the EECS (evapourative emissions control system) to meet emissions specs this goes via the charcoal filter. Most American fuel pumps have vapour recovery systems on them as well. That corrugated plastic sheath that goes over the nozzle & your filler neck. As a result the breathers are a little slow on these cars - If I fill mine too quickly I can trigger the nozzle even with a fully operating breather. So - fix your charcoal cannister. It's not breathing correctly. Wheeze !!!!!!!!!!

The integrated fuel pump & sensing modules (with floats) are accessed from under the back seat. The floats bob up & down as the fuel sloshes around & can get a bit noisy with age. Your gas gauge has a damper on it or it too would wave up & down. Even with the damper you have probably noticed that it shows a different level if you are going up or down hill or cornering hard. Don't replace the modules unless the pump or gas gauge fails. They cost about $450 for both. The pump side is more expensive.

Here - The fuel pump on American cars is on the drivers side

c240classic

Glyn, humour me on this one

The fat tube going into the charcoal tank at the top is gas tank vent. What if i just unplugged it from the canister, it means that vapors can escape into the air at any time. I can put a small generic inline charcoal filter on it and leave it unplugged.

Now this means that the there will be no vaccumm in the canister but what i can do with that part is put a vaccumm hose to the top and put a one way valve in it, flowing into the charcoal tank. So when the purge wants to draw, it will open it, otherwise its holding vaccum.

Now i know the consequences, if i over fill the fuel tank, instead of fuel coming out into the canister , it will drip down. What do you experts think ?

Glyn M Ruck

Don't mind humouring you - Legalities aside - I would maintain the standard Benz configuration. If you don't you stand an excellent chance of triggering endless codes of the following nature.

P0440 Evaporative Emission Control System Malfunction
P0441 Evaporative Emission Control System Incorrect Purge
Flow
P0442 Evaporative Emission Control System Leak Detected
(small leak)
P0443 Evaporative Emission Control System Purge Control
Valve Circuit Malfunction
P0444 Evaporative Emission Control System Purge Control
Valve Circuit Open
P0445 Evaporative Emission Control System Purge Control
Valve Circuit Shorted
P0446 Evaporative Emission Control System Vent Control
Circuit Malfunction
P0447 Evaporative Emission Control System Vent Control
Circuit Open
P0448 Evaporative Emission Control System Vent Control
Circuit Shorted
P0449 Evaporative Emission Control System Vent Valve/
Solenoid Circuit Malfunction
P0450 Evaporative Emission Control System Pressure Sensor
Malfunction
P0451 Evaporative Emission Control System Pressure Sensor
Range/Performance
P0452 Evaporative Emission Control System Pressure Sensor
Low Input
P0453 Evaporative Emission Control System Pressure Sensor
High Input
P0454 Evaporative Emission Control System Pressure Sensor
Intermittent
P0455 Evaporative Emission Control System Leak Detected
(gross leak)
P0456 Evaporative Emission Control System Leak Detected
(very small leak)
P0457 Evaporative Emission Control System Leak Detected
(fuel cap loose/off)

c240classic

Problem fixed! I had the shutoff solenoid valve assembled the wrong way. Only two possible ways to place the spring in it, always open or always close. I had it set on always close. Now i can put gas in my tank :P
However my P0442 is still there, i might have to bite the bullet and take it in to the dealer to get it fixed, not sure they really have a handle on it either, probably will start replacing the canister and purge and different parts till the problem goes away and i go into debt!
Thanks again for all the expert advice folks

Glyn M Ruck

Did you cancel the code?

Jbell

can anyone explain how this dual tank system works?

does the pump feed from both tanks evenly? does one tank feed the other?
how exactly does it flow?

C230V6

Glyn M Ruck & Guys.

I have a 2006 W203 C230 V6 Sport Sedan Avantgarde. The Fuel Level Sender has a metal pipe, covered with a spring, that some how bents inside of the tank. I checked the inside of the tank as the under side of it. There is no impact damage or deformation of the tank. The FLS I had to replace twice now.
I also experienced the same problem with fueling up as you did O/T. I'm just not sure if the way to fix my problem will be the same as O/T's model? Please: nix:

Regards