mtlapinski

Hello,
My 2002 C230 (119k miles) runs out of fuel when the gauge indicates half full. From reading around I have come to the conclusion that the sending unit is faulty. Which side is the sending unit on and which side is the fuel pump on? I dont want to take apart the wrong side and order the wrong part. Also, if anyone has access to the WIS for this procedure I would greatly appreciate it.


-thanks
-mtl

samaritrey

Actually there are two sensor units with the fuel pump built into one.

mtlapinski

Great, which is which? I am guessing the one that is broken is the one without the fuel pump.

-thanks
-mtl

johnand

Like Trey said there are 2 sending units, one on each side of the tank, and your car should have the pump/sending unit on the drivers side. So, if you are having fuel level sensing problems, you need to replace BOTH sending units. Do a search under my name, and I have posted all the WIS documents in several threads.

mtlapinski

The way I understood it, one sending unit sends fuel to the side with the pump.

I am assuming that my fuel pump is OK as the car runs fine, just runs out of fuel with the gauge at half. So the assumption is that the passenger side sending unit is bad and the passenger side saddle tank is full of fuel that cant be pulled out of it.

Why do you recommend replacing both of them? Im questioning it because the units arent cheap.

-thanks
-mtl

Glyn M Ruck

The car takes readings from both sender units & averages the input from both saddle tanks to the gauge. They are indeed expensive. Benz recommends changing both at the same time. You might get away with just one if you can identify the faulty unit. Take both out under the rear seat plates & measure them. You have an early car. Pump side is not consistent from my experience on this board so have a look. Most older cars have the pump on the drivers side (US). That said my own car is opposite.

Here is WIS document for older cars:

https://mbworld.org/forums/attachmen...vel-sensor.pdf

mtlapinski

So I pulled it all apart after waiting for the guage to show 1/2 a tank. The side with the fuel pump(passenger) is almost empty and the side with the fuel level sensor (driver side)is full.

Does the fuel level sensor have a pump built in that sends the fuel to the fuel pump side? (from driver to passenger)

OR

Does the fuel pump sump the fuel out of the driver side and I should start looking for a clogged or kinked line?

Thanks for the help, I think I'm close to fixing this one.

-mtl

Glyn M Ruck

There is only one pump. Your car has the pump where mine does. You are going to have to check all the lines & the filter.

mtlapinski

Hmm ok, So how does the fuel get from the sensor side (drivers side) to the fuel pump side (passenger)?

Also, isnt the fuel filter after the fuel pump? or does the pump suck the fuel through the filter before it sends it on its way?

-thanks
-mtl

Glyn M Ruck

The filter is after the pump & contains the fuel pressure regulator. The system is self balancing between the two saddle tanks with pipes & breathers.

As you can see this is not a straight in and out filter.



https://mbworld.org/forums/attachmen...uel-filter.pdf

mtlapinski

Ok, Looks like I will be taking it all apart this weekend to see what is clogged in the balancing system.

MB///HRV

I assume the above wis covers my 03 c230k sedan? I'm having a fuel leak in the rear of the car. Noticed it after filling up and car sitting. Have been noticing a fuel smell after filling up lately but goes away. always outside car never smells inside.

mb of cherry hill is telling me it is the left sending unit at $1,040 but they recommend doing both sides for something like $1,490 +tax total.

by the looks of the wis, i would assume the sealing ring could be purchase seperately, no? but with 155k does it make sense to replace it? whats the avg life expectancy on the sending unit? dont want to just replace the seal only to have to be back in there in another 10-20k miles.

mtlapinski

For $1490 I will:

- drive to NJ from Boston
- supply both the sending unit and fuel pump
- throw in a fuel filter
- do the job
- test drive and top off the gas tank
- mow your lawn
- do the weedwacking
- empty the dishwasher
- go home

serious as a heart attack =)

-mtl

MB///HRV

Lol nice. What does mb estimate the hours of labor on this? Thinking of just ordering the seal and doing it myself without the changing the unit. Getting more clarification from them in the AM as to where EXACTLY the fuel leak is.

samaritrey

^ lol so true get the parts from rmeuropean if needed also if you have a fuel leak I doubt they pump could cause that since it is inside the tank?? I would check around the fuel filter and filler if i were you

Glyn M Ruck

Yes it covers your sedan. I would replace the sealing rubber. I would not replace senders until they fail. They are expensive & can last a very long time.

MB///HRV

Nice. Thanks Glyn! Would you happen to have a part # for the seal/rubber?

Russell Ormerod

if your fuel delivery is not in spec, it will not transfer to the right side of the tank, and you will run out of fuel when you still have fuel in tank. possibly your pump is failing

Glyn M Ruck

^ Agreed!

MB///HRV

Car runs fine. Fuel gauge works fine. Issue is that gas was leaking on ground under driver rear seat. Dealer traced back and says it's sending unit.

Glyn M Ruck

Fuel pressure s/b 3.8 bar. A lazy pump usually causes starting & driveability problems. But as the whole system is dependent on the integrity of the pump it can cause what you have.

You need to check everything.

MB///HRV

Turns out the top of driver side sending unit is cracked and the seal is not the culprit. Wasn't this an issue on the e-classes ?

Glyn M Ruck

I don't know.

Russell Ormerod

I was posting about mtlapinski problem not yours MB///HRV, sorry for confusion

mtlapinski

Gentlemen, I have disassembled the system and checked for any clogs. Nothing is clogged, I can easily blow through both hoses leading to the fuel pump.


The fuel is definitely not being pulled from the non-pump side of the tank.

I do have one more piece of information. When gs into the tank I cant pump it in fast. The fuel backs up and clicks the pump off as if the tank were full.

This leads me to believe that some other breather is clogged or kinked.

Im close to giving up because I dont see any other hoses inside the tank that I can check or look at.

Any ideas would be appreciated.

-thank you
-mtl