zsjad

Guys, I decided to start a new post, because when I first posted regarding my problem I asked the wrong questions and probably just confused everybody.
The car dies when the tank shows 1/2. When exposing the sender units under the back seat the right half is completely empty while the left is filled to the brim
I really tried hard using the forums, but can not find a reply simple enough for me to understand
The Merc agents in my area says that the fuel is pumped by means of an electrical pump inside the tank, while others mention a venturi / suction type device, driven by the return fuel to the tank, being responsible for the transfer.
The latter school of thought suggests that the remedy lies in overhauling the high pressure pump. I ordered a repair kit from the agents according to the vin number, but it is not remotely fitting the pump on my vehicle. When confronting the agents again, they then explained that for my pump there is no kit available
Can somebody please explain the system workings to me as simple as possible please
Your assistance will be appreciated

kajtek1

Your problem is more model/class related so you might get more direct answers in your class section.
I am not familiar with C, but knowing E and ML, Mercedes is using venturi type suction for inside the tank fuel pumping.
Your model is not recognized by US catalogs, but I found picture of the pump for US model, so confirm it is the same?
When those system, having no moving parts are pretty reliable, any small misalignment or kinked hose can make them non-working.
I don't know who you consider Merc agents, but you really need to find mechanic who knows Mercedes.
Post VIN and then I can match the part.

zsjad

Hi
Thank you for assisting
I cannot really confirm that the pic corresponds to my vehicle, although it looks the same. How do I go about seeing the part names to which the numbers refer to?
The Vin is WDC2030162R011700
What I would also like to know is at what stage the pumping starts, because if it starts right from when you begin driving after filling the tank, i.e. keeping the RH side, from where fuel is being drawn to the engine, full all the time, I fail to understand how the fuel gauge can ever move away from "Full" before the vehicle runs out of gas
Hope to hear from you again soon
Regards

kajtek1

I check EPC with your VIN and it is the same assembly with the exception that part #130 doesn't apply.
The 110 is called "Fuel delivery module"
while 120 "Fuel level sensor with pump"
Part diagram is not explaining working principals, but looks like you have separate level sensors on both sides and computer calculate total tank level.
Not seeing more details, I would guess that 110 is electric pump that supply the engine, 120 is venturi pump that transfers fuel from left to right side of the tank.
As you can see this is not a standard tank, so it will take higher level technician to troubleshoot it.

kajtek1

Thinking about it more, when Venturi pump fails, it usually leaves 5 gallons in the tank, while you are saying 1/2 of the tank.
Tanks on different models can be build differently, but i wonder if by any chance somebody did not reverse the hoses on the tank.
Here is drawing showing outside plumbing.
60 is feed, 70 return line.
Notice that they cross over at the tank.
Beside that the main suspect would be pump #120
The part #203 470 31 41
If that is not too expensive, I would consider buying it.

kajtek1

One more find - ebay lists both pumps for $500 ouch.
Anyway, that picture finally shows some connectors. The right pump is 120 on parts drawings.
You seen 2 hoses on it. The one with the strainer should go to the bottom of the tank, when the other should go to other side with electric pump on it.
Can't see how the houses are mounted, but that gives you the idea.

zsjad

Many thanks again for all your trouble. At least now, when taking out my fuel sensors, I am at least able to consider the various scenarios you pointed out. Your guess that the computer calculates the fuel on board makes sens.

At the agents they more or less convinced me that my fuel transfer is done by a pump inside the tank. This seems to be further confirmed by the fact that my vehicle is fitted with a fuel pump relay as well as a 20 Amp fuse for the pump

Regarding the possible switching of hoses, I can confirm that it is not a possibility, because I have had the vehicle for 8 years and it functioned correctly until about a year ago. At first it would die with the fuel gauge showing near empty and later with it indicating 1/4. And so it progressed until now that there is no transfer at all and it dies when the one half is empty

If the agents were not so convincing that my vehicle transfers by pump, I would have believed that the return was not sufficient and that the high pressure pump was the culprit. Apart from the transfer problem the car is absolutely fine and starts normally

Kind regards

kajtek1

I happen to have mechanical and aviation education, what sure helps on the issue as Venturi is widely used in aviation, but the complicated fuel tanks are probably the only place of use in automobiles.
Reading you last report, the thing was getting worse and worse over the time?
So the only logic explanation would be that either the Venturi on #120 got clog, or one of the hoses changed. Knowing what you are looking for, that should be easy to diagnose?

Plutoe

[QUOTE=zsjad;6918287]Hi

The Vin is WDC2030162R011700
What I would also like to know is at what stage the pumping starts, because if it starts right from when you begin driving after filling the tank, i.e. keeping the RH side, from where fuel is being drawn to the engine, full all the time, I fail to understand how the fuel gauge can ever move away from "Full" before the vehicle runs out of gas.

I regret to advise on your confusion, you must be careful,there is so much spam, speculation and misinformation in this thread that I have attached a diagram of the fuel tank function for your 612.692. It is very straight forward and easy to follow and will answer most of your questions od the CDI fuel delivery system. Be watchful

Hopefully this will clear up for you and others all the previous misinformation and non related confusing pictures!!