Help !

Greetings all. I was sent here from the Mercedes SLK Forum.

I have a 2003 Mercedes SLK 230. Very similar to the Crossfire.

The problem I have is that there is fuel in the charcoal canister.

There is a ¼ tank of fuel and there is no vent line near the top of the fuel neck so I don’t think topping off the tank is a concern.

The fuel warning light was blinking indicating an EVAP issue. After a visual inspection. The cap is fine. All the connecting lines appear to be in good condition.

I used a small bore scope to look in the fuel tank neck and the vent hose no blockage found.

I bench tested the canister shut off valve and the purge control valve. They work flawlessly. I have a 5V reference signal at the fuel tank pressure sensor ( part of the sending unit).

The purge control valve is wet with fuel and is sucking fuel out of the fuel filter MOT port or canister and into the intake causing a rich condition and misfires. (New Mann Fuel filter).

The car is equipped with a four-port fuel filter TANK / PUMP on one end and CAN / MOT on the other as well as a rats nest of hoses and some sort of what appears to be a small in line diaphragm

Part # A0004760055 WAHLER 02W30

I have replaced the fuel rail damper and have 58 Lbs of fuel pressure at the rail.

So … What is the function of the four outlets on the fuel filter?

And ….. Why / How am I getting fuel in the canister ?

Electrically it appears to be functioning….

Any help or advice would be mush appreciated.

Thank you

 

Maybe the hoses to the filter are incorrectly fitted if you have just changed the filter.
Or the filter is faulty.
there is only one line going to the evap valve so the fuel must come down it.
You do not say when the the new gas filter was fitted.

 

onehundred80
I have been enjoying the car taking trips etc.

I serviced the car 10 months ago including the new fuel filter.
All of the connections were inspected. All seem to be ok.
It happened all of a sudden. Just a few days ago.
The low fuel light started flashing and it was running rough.
My first thought was to put gas in it and the
one thing I failed to mention is that I cant put fuel in the tank. ??
I never seen anything like this before.

 

onehundred80 If your suggesting the fuel filter is / may be bad we will cut that thing open. new fuel filter on order.
I seen the other post with the leaking canister.
thanks for the tip.

 

I just had a similar situation with my 2006 base roadster. It turned out to be the gas cap. I had replaced it with an aftermarket cap. I had 3/4 of a tank and the gas light flashed. I reseated the cap and all was good for a weak.
Then it flashed again and the Check Engine light came on. I put the original cap back on and no trouble. You might want to try a new original Mercedes cap. It would be cheaper than the filter.

 

Thank you for your response Driver,
But if the gas cap was faulty then why cant I put Gas in the tank?
It appears to be a sealed system so something else is causing this condition.
I think a bad gas cap would only throw a P0457 code indicating a loose or missing gas cap or leak in the system
open to the atmosphere.
I think I'm ruling out a faulty cap

 

fuel in the charcoal canister is usually from overfilling the gas tank at some point, dont go past the gas pump shut off click.

TANK = return to tank
PUMP = in from fuel pump
CAN = vent and pressure reference to charcoal canister
MOT = outlet feed to motor

 

.



Only thing I can suggest (since I have not heard of this before) is to remove and replace the charcoal canister and find the reason fuel is feeding into it. That system should never have fuel in it so IF you never 'topped off' the fuel and overfilled the fuel tank, there is something that failed in the system allowing fuel to return or being sent down the 'vent' line. I know, it sounds obvious, and what I say here sounds overly simplistic, but there is no other way for this to happen given the information presented. Good luck in fixing this issue!


.

 

Thank you Wings for the input. I cant say that I have overfilled the tank.
After some research I did find three type of filler necks. The one on my car has no vent tube as opposed to the other type that has a vent tube at the filler opening.
So Im not sure if this could be the problem. But Certainly could be a consideration.
I don't believe i did. This happened with a 1/4 tank. If I over filled it I would think I would be having issues almost immediately.
Not that it couldn't happen .....
Shown below is the New style Tank



Old style tank

 

Ghost thank you for the response.
In more inclined to agree that there is something that failed in the system allowing fuel to return or being sent down the 'vent' line.
There's not much to it. I did order a new filter.......its a good suspect.

 

There is an overfill valve at the bottom of the fill tube, this causes the gas pump to shut off when this valve rises and closes the fill tube.
If it was jammed open who knows how much you could overfill the tank.
If it was jammed shut you would not be able too put much, if any, fuel into the tank
The OP says he cannot add fuel to the tank.
This gas filled charcoal filter has occurred before but I cannot find the thread.

 

Your system is different than ours. We do not have dampers in the fuel lines. We also have check/roller over valves in the fuel tank to prevent fuel from leaking out the gasoline tank should the car be inverted in an accident or over filing the tank.
One possibly reason you can not put fuel in the tank is because your canister is full of gasoline and thus there is no way for air to vent out as you displace the air in the gasoline tank with fuel when refueling. Remove the canister, start the car. If you do not get a puddle of gas forming from a leak, drive the car to nearest filling station and try to put additional fuel ( just a few gallons, don't completely fill it) and see if that works: Yes, then check valves in the filler neck are ok; No, then trouble internal to to the filler neck check valves.
REPLACE THE GAS CAP WITH A NEW ONE WITH THE SAME PART NUMBER AS THAT WHICH IS ON THE CAR NOW! No excuse, just replace it with the exact same part number.
Try to get a new unused canister as a replacement or a used one which has not been soaked in gasoline. You can reuse the one you have if you thoroughly dry it out, but it will not have the capacity, nor work as well as a new one.
If you find a small value in the vent line that runs from the canister back to the fuel tank (small white plastic?) get the part number on it and get a new one. It is a two way pressure relief valve. If it is stuck because of dirt from the canister and it probably will be, as the dirt flushed into the value from the saturated canister.
You say you have a good shut off valve on the canister per your test. I'm not convinced of that, but it's your call.
Good Luck!

 

Thank you for the response Zip.
I have a new cap on order.
As for the functionality of the three electrical components they do function as designed. Each one are activated by the ECU. The ECU would indicate a malfunction by setting a code. However there are none.
Im waiting for parts. As soon as I can reassemble everything. I will check the
Three Electronic Components by back probing each device when the EVAP system is on.
12 volts power, 5 volts reference signal and the pressure switch to see if it has electrical continuity.
I did use a small bore scope to inspect inside the lines and found nothing.

 

If you find a new canister, post from where. They are impossable to find.

 

CAREFUL. Do not assume what I put in bold text unless you fully understand how the ECU determines there is a fault in this particular application.
One of the mistakes made during diagnostics is to not do diagnostics and instead, just trust codes without thinking things thru.

I admit that I do not fully understand the sequences involved in the EVAP system. If you fully understand it, fine. If not, be careful making conclusions, as once you turn your mind off to a possibility, you can waste a lot of time chasing your tail.

 

All,
Just looking at the wiring diagram there's not much to it. The ECU get a signal that there is a build up of pressure in the tank. The ECU sends 12 volts to the canister Causing it to close. (INCORRECT: shut off valve causing it to open) The Purge control valve
gets a signal and will scavenge off the excess vapor by pulsating and allowing engine vacuum to burn off the vapors. Then there is the fuel filter There is a check valve or a mechanical device inside that is part of the EVAP circuit. I plan on an autopsy
as soon as the new one arrives. I need to know its function. I have a Leak tester / smoke machine that I will connect as soon as I am sure everything is assembled correctly to check for any leaks.
It seems to me that its a mechanical malfunction and not electrical. I've been wrong before.

 

Anthony C ----- "The ECU sends 12 volts to the canister shut off valve causing it to open" That is not correct.

The canister's shut off value normal position is open. The PCM sends a signal to close the shut off value when it tests the system by opening the purge value so the engine can suck (creates a vacuum) in the system while testing. There is a pressure sensor in the gasoline tank that senses the vacuum during the test.

PS a bad shut off value or clogged vent line often makes it difficult to fill the car with gas. I'm guessing you have one or the other. 1 Bad shut off value. 2 clogged vent line.

 

Zip....
So your saying the PCM sends 12 V to close the valve. That makes more sense. The valve is laying on the bench ......... Yep you are correct my bad .....there is a small spring that holds it open.
See Below.
It seems the shutoff valve is working I tested it again normally open 12v closed. Thank you for correcting me. I'm getting more senile by the minute.
So now where is the vent line? Im asking me that question too.

 

Here is a rough diagram of my EVAP system.
Comments and suggestions are welcome.