Just a heads up for those of you who haven't done their filters yet, do not delay.

My car has under 100k miles on it and I noticed the power beginning to slowly deteriorate, then one day the wideband started showing AFR's in high 16's when in boost and power was down substantially(normal AFR's were in the high 11's at full load). I went ahead and ordered new sending units/ pumps for both sides. Upon removing them I realized that I caught it just in time. As soon as I touched the driver side fuel line clamp, the fitting immediately broke off despite having the metal sleeve inside. The fuel pump connector started to melt into the passenger side fuel pump basket, indicating an excessive current draw from the pumps. After replacing both sides, I went for a drive and the difference in power was amazing. I decided to dismantle the driver's side sending unit and look at the filter. What I found was rather alarming. The filter started to collapse on itself and all the surrounding fuel in the filter basket was black. I took the filter out and my gloves were BLACK from all the crap that was built up inside. Here are some pics of the cut apart filter. The element is completely plugged solid. The black residue is all the dirt falling out of it.

**PARTS LIST**
211-470-51-94 - Driver side sending unit assembly(includes fuel filter, sending unit, pressure regulator, siphon pump etc)
211-470-17-94 - Fuel pump basket (passenger side)
211-471-05-79 x 2- updated green sending unit seals
"125" size MB fuel line clamp(1 time use) or equivalent size fuel injection clamp(DO NOT USE
generic worm clamps)
If you do not have the special "claw" type tool to remove the sending unit retaining rings,then also order the retaining rings.
For those of you looking to do the job yourself here are a few tips.
The job is a little tricky mainly because the 2 sides(driver and passenger side) of the sending units are linked inside, and have to be assembled inside the tank.

-MAKE SURE the tank is below 1/4 before you start, the less fuel the better
-Clean any dirt around the fuel pumps BEFORE you open the tank to avoid dirt falling into the bottom of the tank.
-cover the interior of the car around the working area since fuel will spill
-BEFORE YOU open anything, disconnect the fuel pump connector on the passenger side and make sure it is not melted/damaged. If it is, STOP, and go order a connector repair kit from the dealer.
-Depressurize the fuel system via the pressure port on the fuel rail.
- gently loosen the fuel line clamp on the driver's side.
-Fuel hose might be seized on the sending unit, DO NOT PULL ON IT. Gently get in between the hose and the plastic fitting with a small 90* pick and work your way around untill you can twist the rubber hose off.
-*This is important*, before you take anything apart, assemble the new unit( both sides) on the bench to get an idea of how everything fits together. The driver's side sending unit will be linked to the passenger side fuel pump basket with 4 fuel lines total +1 electrical connector.
The fuel pump basket is made of two pieces which will need to be disassembled, dropped in the tank, and then assembled inside the tank which is why it is best to figure out where everything goes outside the car.

-Undo the passenger side first, LOOK, take pictures, do whatever you need to memorize how everything sits in place. If you do not feel comfortable doing the job submerged in gas, just stop. Disconnect the Driver side sending unit lines from the basket (looking at the new unit for reference) ** then separate the basket and take out the fuel pump halves.
-Remove the sending unit on the driver side , install new sending unit, you will need to route the lines to the passenger side.
- make sure to remember which way the top caps face, driver's side will be indexed with an arrow on the sending unit and a line on the fuel tank. The sending unit caps will be spring loaded so they will require some force to compress and to install the retaining rings. Lubricate the green sealing rings with some silicone to make installation easier.
- refit everything in place. If you are lost, reassemble the old parts on the floor and use them for reference.
-Do not forget to clip in the large fuel line coming from the sending unit into the fuel pump basket.
-Some lines/electrical connectors will have very little slack so they will need to be routed in a specific way. (which is why it is important to see how everything is routed BEFORE you disconnect everything).
-Reassemble everything, leave the service covers off leaving the sending units exposed, clean up the top of the tank.
-First, turn the ignition on, and watch the fuel line closely, if you have any leaks, stop and retighten/change the clamp.
-Drive to the gas station with the sending units exposed, begin filling the tank, watching the top of the tank for any leakage.

 

I've long suspected that clogged filters were responsible for the melted wiring that people had reported.

Personally, I think there might also be a few "blown motor" threads that were the result of a car with big HP and old fuel pumps/filters where the engine simply starved for fuel and went super-lean.

Larger 550cc injectors might be a temporary way to mask a fuel delivery problem, but ultimately it seems important to get those pumps/filters swapped out at the correct interval (Which I believe is something like 60K)???

Great info and photos!



-G

 

Thanks for sharing, how had was the change, could you write up a quick DIY?

 

I agree and thanks! A DIY would be great!

 

Part numbers and a quick DIY would be awesome!

 

Yes, please. How do you change the fuel filter.

 

By installing a new pump.

 

According to the pic, it looks like you can seperate the filter from the pump, to change to a new filter. Am I wrong?

 

it is one assembly

 

Updated with a couple of pointers and part numbers. The fuel filter is not replaceable. It is part of the sending unit on the driver's side

 

Had the melting/fuel leak issue on mine, and ended up having to replace both sending units. Luckily I'm covered on this now. On to more maintenance!

 

Thanks for sharing.

 

Strange ... I distinctly remember mine twisting off. Perhaps design changed.

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Wonder what it would cost to have a shop do this ? Looks more involved than I want to get.

 

Just looked up those parts ........ over $1500 parts alone ?!

 

Yup! That is why I wanted to know if we could just replace the fuel filter.

Some say no, that you have to replace the entire fuel pump assembly that also has the filter.

Some say yes, but I have not seen proof of that being done or how its done.

 

Separating the basket would be the biggest problem. The plastic gets very brittle after being submerged in gas for a few years. I was not able to separate my old one without breaking.

I would be inclined to bypass the filter completely, and run a high flow unit mounted externally for easy servicing

 

That would be the only other real solution if you didn't want to replace the pumps. However replacing the pumps in these cars after 60K is never a bad idea, just don't replace them with someone elses used pumps.

 

it a good DIY but the unit is expensive
Im sure fuel injector cleaner and other product help to clean up the filter a bit.

 

The fuel pump connector started to melt into the passenger side fuel pump basket, indicating an excessive current draw from the pumps is exactly what happened to mine too:

 

That's exactly what happened to mine, except it was so bad you could actually hold it up and see THROUGH the part.

 

My pumps went bad at only 67K miles. Replaced them so I guess I am all good now.

 

Stuff like this pi$$es me off. I was all set to put this behind me and just put it down to routine maintenance to replace pumps/sender every 60 to 70K (if I keep the car that long), but this is downright dangerous - heat melting stuff and exposed/leaking fuel. Mercedes really should do something here.

 

Lelix... Thanks a bunch! Exellent. When I do mine I will try more pictures.

Coming up on 130k and I have the fuel smell at fill up so I need to get this done.

I will probably make my own tool to remove the retaining rings. Saw that on another thread.

EDIT - Why do you need to replace the passenger side basket?

 

Wait a minute, I was told by Mercedes that the fuel filter/pump is an integrated unit of the fuel tank. Is that not true?

I would like to replace my fuel filter rather than rely on fuel system cleaner, etc. Soo, what's the actual story on that?