C220 CDI Fuel tank problems.

[Smokin..o0O]

LastMinute.
I did not realise that site with merc info was well known on here.
I spent the best part of 1 day searching the net and it was a PM on another forum that directed me to the site.
On the main page http://www.detali.ru/cat/oem_mb.asp enter VIN and the model and spec of the car is listed.
Parts 110 and 120 are the 2 units I have been referring to in my posts.

Part 110 A2034703294 AUXILIARYPUMP £116.92
This is the driver side unit which is nothing more than a plastic vessel with inlet and outlet connectors. The fuel pickup hole on this is not visible though.
The description "AUXILIARYPUMP" is very misleading.

Part 120 A2034701341 MOUNTINGPLATE £221.61
This is the passenger side unit. Described as a mounting plate. This unit carries both inlet and outlet fuel line to and from the tank, and also internally to the driver side unit.
Seems just a tad expensive for a "mounting plate"

I am in the process of removing both these units right now. If I am successful, I will take some pictures and hopefully post them here for you to see.

There are no pumps of any kind that I can see inside this tank. The only electrical connections entering the tank are the wires connected to the sender unit.

 

[Smokin..o0O]

Here I am back again with just a little diesel odour surrounding me
Both units and internal connecting pipes have been removed from the tank.

I have some pictures that show all the parts of the fuel delivery system

#1 shows both units connected as they would be in the tank and looking back from the front of the car.
http://homepage.ntlworld.com/smokin/tank/1.JPG

#2 shows merc part number A2034701341 "MOUNTINGPLATE" ,the passenger side unit as it would be seen when looking forward from the back of the car. The fuel out connector on top is connected to the clear pipe which then connects to the driver side unit.
The fuel return connector leads down through the metal pipe inside the spring and into the yellow plastic part which supports the connector for the black pipe.
The white disk at the bottom of this unit which is in line with the connector and black pipe, is where i suspected the valve to be but early inspection has revealed nothing of the sort. I still believe it is there for a reason.
The spring is to keep the yellow part which contains the fuel intake, pressed down on the bottom of the tank
http://homepage.ntlworld.com/smokin/tank/2.JPG

#3 shows merc part number A2034703294 "AUXILIARYPUMP", the driver side unit. The electrical connector is for the sender unit signal.
Only the 2 smaller fuel pipe connectors on this unit are used, top left connects to the clear pipe, and lower right connects to the black pipe.
This unit also emplys spring pressure to keep it located on the bottom of the tank.
http://homepage.ntlworld.com/smokin/tank/3.JPG

ps1 shows the lower end of the passenger side unit where the black pipe connects.
http://homepage.ntlworld.com/smokin/tank/ps1.JPG

ps2 shows the same unit viewed from below with the black pipe disconnected.
The square hole on the bottom of the yellow part is the fuel intake.
http://homepage.ntlworld.com/smokin/tank/ps2.JPG

ps3 shows the connector for the black pipe. Although the pic does not show it very well, all that is inside that yellow connector is a sort of "nipple" affair that mates with a hole in the connector on the black pipe.
http://homepage.ntlworld.com/smokin/tank/ps3.JPG

I am still not any wiser as to how these units decide which side of the tank the fuel should be taken from, and that is my main problem.
My mind just keeps going round in circles now so I think I'll take a break and try to get this diesel smell form my skin.

 

[BlackC55]

It only takes the fuel from the passenger side to the engine. That is definite. I think you have a problem with the venturi on the drivers side sender. I have just read all of your posts and thought about it again.

If, as soon as the drivers side is empty the engine stops the problem will be with the way the senders are distributing the fuel. I think when the passenger side is empty normally the fuel in the drivers side is used (how I don't know)

 

[Dieselman]

The larger unit looks as though it may have a float inside it which allows fuel to be drawn when raised and then shuts of when there is no fuel so fuel is then drawn from the other pickup.

Just a guess.

we need a pic of the other unit.

Found it. You didn't provide the right linky.

http://homepage.ntlworld.com/smokin/tank/3.JPG

So what's inside the canister?

 

[LastMinute]

Mmm, diesel. Try combining it with old engine oil for that extra special aroma...

They really do say a thousand words, don't they? Clearly I was barking up the wrong tree with the pump theory.

Dieselman's suggestion that the issue may be with the right-hand unit sounds much more plausible. If something inside it is jammed it may never try to draw fuel from the left-hand side of the tank.

The last fuel system I looked at in any detail had, IIRC, 13 tanks, 20-odd pumps, about 40 shut-off valves and umpteen level sensors, with four engines to feed and four computers to control it all. That didn't work properly, either...

 

[Dieselman]

The last fuel system I looked at in any detail had, IIRC, 13 tanks, 20-odd pumps, about 40 shut-off valves and umpteen level sensors, with four engines to feed and four computers to control it all. That didn't work properly, either...

Apart from the four engines it sounds just like a Jaguar.

 

[LastMinute]

LOL
Actually, it was a Rolls-Royce.

 

[Smokin..o0O]

Hi all.
Thanks for all the input and suggestions.
Sorry for the wrong link

The driver side unit seen at http://homepage.ntlworld.com/smokin/tank/3.JPG
does not seem to contain any moving parts.
It does have various chambers within as I discovered when I removed it from the tank.
The unit was full of fuel and it took about 5 minutes to get the fuel to pour out.
It was a case of twisting, turning spinning and shaking to get the fuel into the chamber nearest the outlet.

So it is more than possible that this unit does control the take up of fuel from the passenger unit, but I can think why this would have happened, maybe just a glitch, an airlock or something silly.
Now that both units have been out, and theres no obvious reason for the problem, I think as soon as weather permits, I'll put them all back in and give them another chance to behave.

I still can't get my head round the prices quoted for the 2 parts. If anything I would expect the driver side unit to be the more expensive of the 2.
Oh well, I'll sit here a while and listen to the rain on my roof hoping the skies clear soon

 

[Nicksmith_75]

hi there. just spent 2 days on a c220 cdi with the exact same problem. the fuel filter is supplied via the transparent pipe on driver's side, through the nearside. now the return goes in the nearside and into the mysterious black pipe to the driver's side. there is a small opening at the bottom in the passenger side, which creates a suction and pulls the fuel from the passenger side to the driver's side. on idle the driver's side runs dry, but on revs it's fine. contacted everybody i know, and mercs have told me to replace both sender units at a costs of £450. i personally can't see what can go wrong on them as i've had both units out and there is nothing mechanical or electrical that can go wrong. tried a second hand supply pump on engine. thinking if fuel delivery not sufficient, won't be enough return to create sufficient vacuum to draw fuel from passenger side to driver side. no different. mercs say common problem. senders rectify. not changing it. sending customer to mercs.

 

[ace8800]

HI, im new to this, just been reading this tread, i have the same problem with my car, what i wanted to know was if Smokin..000 managed to get the car running again, if you did, what was it?? was it the pump at the end and did u end up replacing it?

thanks

 

[banihwah]

Hi there, I seem to have exactly the same problem as Smokin oOo. How did you resolve this? Was it the senders in the end? I've just had a rather large quote to fix the problem, are there really no options for the parts?

 

[E270 Owner]

What was you told is the problem ?

 

[JonBuck]

Saddle tank fuel supply

Just been through this nightmare! The problem in my case was with the high pressure pump, this returns fuel to the passenger side of the tank and then a proportion is sent via the venturi to the drivers side. The fuel from the high pressure pump must be sent at a high pressure in order for the venturi to work. There is a plunger of some kind in the pump that fails. Hope that this is of some help.

 

[E270 Owner]

A weak HP pump can/will give the 1/2 tank indicated but no diesel to engine syndrome.

I have also seen this at @ 1/4 tank as well due to HP pump fault.

The venturi is too weak to move the fuel across the saddle tank system, one sides dry as a bone the other side full.

The left tank stays full as this is the return, the right side is dry the HP pump feed.

What happens is you fill up as the fuel nozzle fills the right side tank (its on that side),
then runs out again when that tanks dry with 1/2 a tank indicated.

There's not enough pressure for the venturi effect to be created.

The yellow highlighted 40 in the image is the fuel tank electric pump,
this pressurizes the fuel system up to the fuel filter and HP pump.

The HP pump returns fuel on the low pressure side if this is too weak it cannot create a "venturi"

"The Venturi effect is the reduction in fluid pressure that results when a fluid flows through a constricted section of pipe"

 

[JonBuck]

Saddle tank fuel supply

On my C220 cdi, item 40 is there to prevent the effects of cornering on the fuel supply. Its like a mini baffle plate. Fuel is drawn from within. There is a low pressure fuel pump mounted above the high pressure pump, at the front of the engine, which draws fuel from the filter, and supplies the hpp.