The amount of stuff packed into the fuel tank of a W212 is pretty crazy. I don't even know all of what I replaced today. But it doesn't matter, I didn't need to know--just pull and replace the 2 complex assemblies, one on each side of the saddle tank.

I have had a code telling me that the low pressure fuel sensor reading was "implausible" since before I got the car. I had that part on hand and was getting ready to change it out when I smelled fuel occasionally outside the car. I removed the rear seat and the covers on the fuel assemblies and found that the side without the low pressure sensor was also leaking. This is the blue side with no fuel connection running out the top of it. I'm still not sure where the actual leak in the part was, but I still have the part and will do some inspection later to try to figure that out.

This was a really straightforward job and only took about 2 hours. The hardest part was finding fishing line near me. I needed this to pull the new tubes through. Maybe you don't need it, and it's a little bit finicky, but it worked for me.

Then there are a few types of plastic connectors for fuel and for electrical connections that you will need to know how to operate. I'll post pics and some more details once I get all the pics offloaded from my phone.

I managed to only break one unnecessary piece of plastic which holds an electrical butt connector to the top of the blue module. And I didn't spill any fuel outside the recessed tops of the ports. Overall a win.

Another symptom that I think was related: a couple days ago when accelerating slowly and then suddenly starting to get on the throttle, it felt like the engine cut fuel for a fraction of a second before accelerating again. This didn't result in any codes. I think the low pressure fuel circuit couldn't keep up. Whether or not the sensor reading was plausible or not, the filter was probably heavily loaded. I intend to open the filter to inspect it as well in the next few days.

 

Congrats on fixing your tank issues. Hoping it's all right now.

There may be electrical issues playing against you there.

> NOISY HARNESS:
Last time I dealt with that I found the small signal sensor wiring was mixed up with the pump noisy harness. So I split the noisy run apart.


> FIXED VOLTAGE:
There's a new 5mn fix for lean/weak accelerations: self-regulated stable voltage!

When Bosch "dynamic voltage" is in use, engine accelerations causes the ECU to limit serpentine drag by lowering ALT voltage... ouch!

Try using fixed stable voltage by disconnecting ALT LIN, you may realize every chassis module works far better under stable condition.

Specifically during accelerations when mixtures must be enriched, not leaned out.

1. reset all faults to clear soft-crashes
2. reboot chassis to relearn networking
3. unplug ALT LIN to get self-regulated 14v
4. monitor Batt on IC Displays 14v/ low Amps

Enjoy throttle + shifts improvements!

 

Nice work. I'm looking forward to the pics.

Amazing! It seems as if I'm always breaking something when doing almost anything on my W212

 

Might be electrical issues indeed. The fuel cuts are back today. I haven't unplugged the alt LIN yet, but I did have the headlights manually switched on when the cuts occurred.... I'll start another thread about this.

 

OK, so here are the details of what I did:

First, disconnect the main battery. I was wondering if I should also disconnect the aux battery, but nobody else did, so I decided to skip it.

Anyone know what the pros/cons of disconnecting the aux battery are?

Also, the clips that hold the plastic box above the battery are absolutely terrible. Atrocious. You can carefully slide everything around to get it so it looks like it lines up correctly, but as soon as you start the engine it all falls down and there are gaps everywhere...





Next, pop off the bottom of the back seat. There are 2 snap-in clips at the front of the bench and 2 hooks at the back. Lift at the front of the seat on each side until it snaps out. It's very easy. Then lift the front edge of the seat up uniformly on both sides so that the hooks at the back disengage, then slide it out.

Here is where to pull on each side:




You are disengaging these metal loops that are on the seat side from the plastic pockets on the car side:

Metal clips:


Plastic pockets (red circles):




The blue circles show the location of the hooks. I don't think they really have much engagement with the soft seat, but they can hang you up a bit if you aren't aware they are there.

Then pull the recycled matted material off the top of the metal.

Now you will see the tops of the ports that give you access to the tank (this is from a W203, I think, but mine looks the same. I have seen other different styles on W212s, I'm not sure if that's a pre-facelift thing or a different engine type):



Each of those gray covers (mine were black) have several 8mm nuts. Just use a hand tool to loosen and remove. Power tools should be avoided in case you have leaking fuel underneath, since they can make sparks. The sealing system for these covers is kind of dumb. There is a bead of some soft material going around the edge to seal, but there are wires going through that are protected by some kind of felt that acts like a flap to hold the covers on. The little flaps broke right away during the job, but I don't think it matters at all. I just don't like the way the wires are pinched and they break the seal as well... Lift those covers out of the way and try not to break the flaps if you want...

You will be presented with something like this (note I already removed the driver's side lock ring when I took this photo):




I had a code related to my low pressure fuel sensor which is on the driver's side, and I also had fuel leaking from the other module with the blue top which is on the passenger side, so I decided to replace both at the same time since they both need to come out to do the pressure sensor. Since each of these modules has many functions and Mercedes calls them something like "fuel handler" or "fuel delivery module" and I really don't know what to call them, I'm going to refer to them here as the "white module" and the "blue module".

Before doing anything else, clean the hell out of the area around the wires and fuel lines that are on top of the modules. I first shop vac'd them, then used a cloth, then shop vac'd again. As I started disconnecting things and getting ready to lift the modules, I did a few more cleanings and shop vac'ings. I wanted to make sure that any debris kicked up was removed and that I could access every area to do a proper clean before I exposed the inside of the tank.

Definitely have a bunch of disposable rags on hand for cleaning and to soak up any fuel that leaks out. I managed to not get any fuel outside the top of the ports which was not the case in a lot of videos I watched.

Looks like my blue module is from a C218:




Here you must remove the 7-pin connector which has 6 pins in use. There is a tab on the left side that you must press in. The entire connector including the black surround comes out. At first I thought the inside pulls out of the black part, but that isn't so.

Now is a good time to mention that, of course, S-Prihadi has a much better thread addressing some of these steps, you can find it here:

Low and High Pressure Fuel System

And I have stolen one of his pics to show a few things about the blue module:




Here you can get a better view of the tab you need to press to remove the big connector. And you can also see how the butt connector which joins the two harnesses is "slid" onto the top of the module. I was trying to disconnect the wires when I broke one of the tabs that holds the connector to the module when I realized I don't need to disconnect the connectors, I just needed to slide the whole thing out of the way.

On the other side, you have this, or something like it (also stolen from S-Prihadi):



There are 2 3-pin electrical connectors, one of which uses 2 of the 3 pins. They are both Hirschmann style connectors without the extra locking tab. It's pretty difficult to press the tab fully with a finger, so I used the tip of a seal pulling tool (like a tiny metal spatula). I backed it with my thumb so I had maximum control of pressure and angle so I didn't break anything, then just wiggled the connectors off. I don't know if the connectors can accidentally interchange, but I noted which connector had 3 wires and which had 2 (shown in the above pic, mine was the same).

The fuel fitting is very easy to remove, but note, if you didn't de-pressurize the fuel system from under the hood, it will spray out about 50mL of fuel. The fitting is disconnected by pressing it down. You will feel it move about 3mm. With it held down, press the side of the fitting away from the side the fuel line comes out. There is a piece there that slides in. With it held in, slowly lift the fitting up off the module. It's kind of like slowly releasing the pressure in a shaken bottle of soda. Put some rags down around the base of the fitting and hold it in a position where the fuel leaks out slowly until it stops. Then clean up the rest of the spilled fuel and toss the rags.

At this point, you have everything disconnected.

Now you need to remove the lock rings. I used this tool which someone else suggested in another thread:




It's probably not the best tool. It's a bit finnicky and I couldn't use it with the arms locked in any position, I had to leave them a bit loose. I thought there was a danger of stripping something out because of this, but I was able to make it work. There is probably a tool which is sized better for these particular lock rings.

Get the tool situated in 3 of the cutouts in the lock ring, attach a 1/2" breaker bar, double check that the tool is still seated as you apply pressure, and give it a ton of torque until the ring pops off. Do this on both sides. Then clean again because you're about to expose the fuel system. Also make sure you don't have any loose sockets or tools lying nearby that could fall in.

Get the lock rings out of the way.

If you're only replacing the blue side, your job is a bit easier. The white side has the crossover fuel lines attached to it which need to be fished across. The blue module is a standalone thing that will just hook to the hoses which are already there.

Since I was doing both, I first got the blue module out of the way. As you start to lift the top of it, you will be pulling a spring loaded "hat":



It might disconnect from the base. This is fine at this point. It won't go too far because of the electrical connections holding the two halves together. The bottom part is attached to two fuel lines from the white module:

At this point, I realize I need to take some more photos, so this thread will be continued...

 

This is what the electrical connections holding the two parts together look like:



They're a pain to unclip with the limited space and you don't need to, so I left mine attached.

You just need to unhook the 2 fuel lines. One of them is snapped into a plastic clip and doesn't go anywhere, it just dumps fuel into this module from the other one presumably (or is sucks out fuel when the level gets high? I don't know, but would like to):



The other hose has a quick disconnect like the top of the white module. This is what the tab looks like that you need to depress:




Same as the other one: push the fitting down, press the tab, then lift. The unterminated line can just be pulled out of the clip. Then remove both parts of the blue module.

At this point, I attached long pieces of nylon fishing line to the ends of each of these tubes and tied the other ends temporarily to one of the locking rings so the ends didn't fall in.





The other side just pulls out with the hoses. For reference, here is roughly what the whole system looks like inside your fuel tank:




Those lines were originally white.

By pulling out the white module, I then pulled the fishing line across the tank and out the side with the white module.

I removed the fishing line from the ends of the old tubes and tied them securely to the ends of the new tubes. I made up some knots and they seemed to work. Keep in mind you'll need to remove the lines on the other side with limited space without dropping any pieces of cut line into the tank.

On the white module side, feed the lines through the space in the middle of the tank and try to feel them through as far as you can. In my case, they went all the way and I didn't need to pull very far with the fishing line--just about 6".

Now you can take your new blue module and clip the quick disconnect fuel line to it, and place the other line in the clip. Here's how the quick disconnect looks installed.



Then clip the wires from the new blue module into the hat piece. There are two connectors of different sizes and you can't mess them up. Place the spring loaded rods into the bottom half and press the whole thing down.

Now you do the reverse of removal. Hold the top of the blue module down while you start the lock ring in the notches and turn it a little bit to hold everything in place. Then get the same tool you used to remove the lock ring and put an ungodly amount of torque until the ring snaps fully in place. Fully in place means this:





The raised red sections of the locking ring should end up under the bumps in the tabs on the tank side (blue).

Once you get both modules back in and locked, just snap all the connectors back where they were, replace the covers and the recycled mat, and clip the seat back in.

It's way easier than I thought it would be.

 

Here is the video that taught me how to remove those quick disconnect fuel fittings:

 

I finally got around to opening up the fuel filter. I can't say it was very enlightening. I was not able to find the source of the leak in the module cover and the filter itself did not seem clogged, though I don't have a new filter to compare to. Possibly the flow rate through the filter is greatly reduced from new due to the buildup of a thin film clogging the pores, rather than a mass of particulates.

The filter itself has a part number on it but I couldn't find a picture of it online. A 2C5 316 42 72 Made by Mahle.

 

That is already considered very dirty fuel filter element, if for gasoline use.
Good that u replaced it

 

I've inspected lots of oil and diesel filters, but this is my first time doing forensics on a gasoline filter!

 

Diesel usually are dirtier, due to its habit of growing baby algae.
However gasoline can produce varnish like coating.

Below is my outboard engine Fuel Vapor Separator.
See the reddish coating, that is some kind of varnish. This is a 15 years old unit.


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.


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My filter system is super duper clean & robust....but it can't filter out chemicals in the fuel which will eventually produce varnish if
engine is not being used often enough.

Boat used to have twin 275HP diesel engines. So I maintained its old filter system. 10 microns>>>2 microcn Racor . Turbine seriesd 900, 4 units serving 3 x 250HP outboards ( re-powered )
https://www.yachtboatparts.com/racor...040-3553-p.asp
Supposedly not for gasoline, due to its plastic bottom cup, in US gasoline version need steel bottom cup.



This unit mechanical water separator is very good.
Its media filter element also has aquablock to not allow water to pass thru.

 

Yeah, it seemed like there could be a decent amount of varnish, but it was hard to say without seeing what a new filter looked like.

That's a cool setup. What kind of engines does it have now?

I would like to see the whole boat

 

It has been repowered and lenghtened by 1.6 meter the boat.
Re-powered with Suzuki DF250 x 3 units

It is a very old boat, 1995 production. US made. Now the company already chapter 11 in 2008 I believed.

Its handling is a piece-of-shi-eet
Thus I modified it and now it handle so well.

This is how originally is before modification : Sister boat in USA


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This is mine ( co-owned )




Re-arrange weight distribution and improve center of gravity and yada yada, plus add a 1.6 meters hull length



The garbage 500 hours short lived engine. US made, this is a GM based diesel engine 6.5L V8 turbocharged aftercooled, Hummer used to use this engine if I remember right.
So it was inboard diesel with regular shaft and propeller, not sterndrive.


Here is the engine details : https://www.ebay.com/itm/176777088922


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After completion of hull extension and tripple outboard re-powering. Was 29 knots max, now it can hit 39 knots max.



This is a 2006 photo.






Now we never used it anymore, since the kids have grown up and are out of country.
Engine need to be thrown all away and get new one. Too much money, not worth it since the use is under 20 hours a year.


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