Details and organised: petrol tank is 1/4 full and pump is empty.

[keithmerc220]

Fits all Mercedes-Benzes equipped with a saddle tank.
If you've ever been in the same boat as me and noticed that your gasoline gauge reads just 1/4 full, then this is for you:
The gasoline supply lines within the tank have likely grown brittle or broken, allowing air to enter the fuel pipes.

It is only necessary to repair the "fuel level sensor" on the left hand side of the saddle tank, not the pump. This set includes all three gasoline pipes that are needed.
Make it yourself is possible. Tool for removing gasoline tank lock rings, which has a rather long 1/2" bar:

[keithmerc220]

[keithmerc220]

To begin, fill the tank to a level of around 20 litres. You must still drain the left side of the saddle to a level of around 20 litres even if all the fuel is in the left saddle.
Take off the two covers (found beneath the back seat) using the four bolt head screws on each.
Turn the lock rings using the removal tool to unlock them. The top connections (on the left side of the saddle) may likely leak, so you'll need to use clean rags to wipe them up.

Undo the fuel pump connectors on the right side of the saddle and tie a string around one of them. (unlock connection with two push clips and one gasoline supply button—yellow)
While keeping an eye out for the fuel level float, remove the fuel level sensor assembly from the left hand side.
Now secure the ends of the three new pipes with the string. Carefully insert the LHS fuel level sensor assembly into the LHS saddle, wiggle the pipes through the saddle's hole that connects both sides, and last, bring the ends of the pipes into the RHS saddle.
Before you connect the pipes to the gasoline pump on the right side of the vehicle, make sure the fuel sensor assembly on the left side is situated appropriately.
Prior to installing the lock ring, ensure that the spherical washer is snugly positioned around the plastic housings.(The ring should have a blue mark; line it up with the attachment point's blue mark.)
Turn the ring (pushing down on the washer) with the tool until it snaps into position.
Be sure to fill the tank halfway.
Turn the key to the second position and keep it there until the gasoline pump stops; do this many times.
Make sure there are no leaks or tears around the lock rings by running the engine for a while.
When the water is clear, fill the tank to the top and check for leaks once more.
Put the covers back on after that. (I reinforced the entry locations with more rubber to avoid wire chafing.)

Things that go wrong:
1) You can't actually get the gasoline connectors to go to the wrong lugs, but the big one with the yellow button connector at the top of the fuel pump. One with a black rubber ring or gland goes to the one below it, and the one below that gets the one without.
2) If there is any gasoline leaking around the lock ring, remove it, turn the circular washer around by, say, 90 degrees, and then lock it again.
3) As the air is being pumped out of the tank, you may hear gurgling sounds coming from it.

Here is my clumsy description of how the saddle tank works:
The high-pressure fuel pump and fuel quantity control valve are located on the left side of the engine, and the fuel pump transfers gasoline from there to the engine through the big yellow button connector on the top. No problem.
To make sure the petrol pump gets the most fuel possible, empty the left side saddle in preference of the right side.
In order to do this, the gasoline is pushed to the left side fuel level sensor assembly via an additional pipe. From there, it flows via a nozzle submerged in fuel at the base of the assembly, which forces fuel into a pipe that recirculates to the right side saddle.
It will not be noticeable until the gasoline level drops, at which point the leak will become apparent and air will be able to enter the fuel circulation pipes, therefore a leak in these latter two pipes is actually not a problem. In such case, air is sent to the right-hand tank and the nozzle stops working.
In this scenario, there is petrol remaining in the left side saddle, according to your fuel gauge, but there is no fuel in the right side pump.

[ianwh4]

excellent article. Are you asking which part—the left side seder or the one with the floats—has failed? I'm having the same problem. Tell me how you determined which one was defective.

[ML350_Colin]

Every morning before I turn on the ignition, I hear a gurgling sound coming from the tank. I really hope I don't have to deal with this problem, because it seems rather complex.
I have been pursuing this for the past three months, and chatgpt has sent me on a diagnostic house tour.

[CyberNinja]

Chatgpt isn't perfect, that's why. Make sure you don't put all your eggs in the basket.

[Rashman4u]

it has never happened to me before!

[ML350_Colin]

Yeah, I got that figured out now.
It turned out to be a nicked o ring on a leaky pipe after it warned me it may be a lift pump.