Clk 270 cdi fuel just in one side of tank?

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alf1956

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Jul 1, 2011
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127
Car
clk270 55 plate diesel
Hi fellow members
I have a 55 plate Clk 270 cdi & I am having problems with the diesel getting to the engine. I recently drained the diesel tank as I had some contaminated fuel in the diesel tank by taking off both of the round cover on the fuel tank & inserting a pipe to suck all the fuel out I then put in 25 litres of clean fuel & ran the car for a while then today the car cut out & would not start & we noticed that the diesel was not getting through & the so we put on a manual inline pump that you press & it pumps the diesel through & the car started but when we took off the manual pump & put the pipes back on the car would not start so we took out the back seat & took off both the round covers on the diesel tank & noticed that the drivers side half of the tank was empty but the passenger side half was full (the diesel tank is like a saddle bag shape with two halves which are connected) so we put some diesel in through the filler which went into the drivers side half of the tank & the car started up & ran no problem but I am now worried about taking the car out in case the same thing happens & the diesel goes from the drivers side & the car cuts out as it seems to be that the diesel feed to the engine is supplied from the drivers side half of the tank but somehow the diesel is not coming over from the passenger side half of the tank? We have had both the sender unit on the passenger side & the drivers side unit out of the tank to see if the connecting pipes were blocked etc but they all seem ok.
 
Is the fuel filter clear?
 
The pump that transfers fuel from one side of the tank to the pickup side has failed.

Are both senders exactly the same?

Is your fuel gauge displaying the correct amount of fuel?
 
The sender was displaying around a quarter of a tank which was correct as I knew there was approx. 20 litres in the tank but my friend who repaired the car did a test run in which he gave it some welly around corners & roundabouts seems to think that with him doing that all the fuel has gone from one half of the tank into the other hence the drivers side tank being nearly empty & the passenger side full but I am now thinking that if that happened surely the venturi pump would pump to make both halves of the tank level, I am right in thinking that?
 
Not sure about the merc set up but had similar problem with a BMW 530d, within the pump sender is a siphon pipe that makes sure that as one side is emptied the other remains level?
 
Hello
The garage has pinpointed the fault as a sticking plunger in the fuel pump which is located on the front of the engine, does anybody know if you can buy the plunger separate from the pump?
 
Sounds more like the dreaded 'Saddletank' syndrome to me. Do a search for this here and on google.
Had the same symptoms on my W203.
Turned out to be the pumps etc in the rear tank were not transferring the fuel across the bridge. Can't remember the exact details but new pumps, syphon thingy venturi spring to mind.
 
I am still having issues with the saddle tank scenario & the car cut out yesterday & when we looked in the tank the drivers side half of the tank was empty. I have had an engine fitted & it came as a bare block with no ancillaries on it so w ehad to take them all off my old engine had problems since then so i am wondering if when replacing all the fuel lines etc they may have got one on the wrong way round, I know the main metal fuel lines from the tank are different sizes so they will be correct but then there are quite a few other fuel line connections on the engine itself & to the high pressure pump & maybe the 2 pipes to the high pressure pump have been fitted the wrong way round as i have had a replacement high pressure pump fitted which was checked out by a local diesel injection specialist prior to fitting
 
I would have thought the only way one side of the tank could be dry is if the connecting pipe is blocked or a pump that does the same has failed
 

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