W203 220Cdi Fuel problem

[paresh]

Hello everyone..

My MY2002 C220 CDi is exhibiting a weird problem - the engine cuts out when the tank gets to about a quarter full. I know that there is diesel in the tank because when I last filled up, I filled it right to the top.

I now carry a gallon of diesel with me in case it decides to cut out before a quarter tank! The last time the engine cut out, I just filled up from my gallon and the car started after a few cranks. Although this has happened only twice it can be quite scary on a fast road when the engine just cuts out - no steering, brakes etc. Basically fuel is not getting to the engine even though there is diesel in the tank. This only happens when the tank gets to about a quarter full (or three quarters empty depending on how you look at it!).

I know that there is still around 20 litres of fuel in the tank because I drove to a filling station straight away and filled up to the brim with around 40 litres and I understand that the W203 fuel tanks hold in the region of 60 litres.

To prevent this happening in future I now make sure that I fill up again when the fuel gauge needle gets just below half full.

I have carried out a search on this forum and can't seem to find an answer.

I wonder if anybody can point me in the right direction as I would like to get this little glitch sorted.

Thanks in advance for your input

 

[kwakdonut]

Fuel filters? I believe there is one in the tank a well as the standard in-line one that is changed every other service or so. Might be getting gunked up....

 

[paresh]

Hi

Thanks for your reply.

I know about the inline fuel filter in the engine bay but I was unaware of the one in the fuel tank. Does anyone know how to access this filter? I've read about the fuel senders at the top of the fuel tank under the rear seat cushion. I may need to remove these to have a look inside the tank. From what I gather, removing the sender units is quite a job in itself.

Can anybody guide me as to where this filter may be?

 

[Stratman]

I've had a look in my Haynes manual for the W203, admittedly it only covers four and five cylinder models, but there is no mention of an in-tank filter, only the one under the bonnet.

 

[paresh]

I've just checked in the Haynes manual as well. I can't find a reference to a filter in the fuel tank either. Maybe we're missing something!!!

 

[paresh]

Does anybody have other ideas as to what else could be causing this?

 

[142 TPL]

Your tank is of a saddle design were your draw fuel from one side up to the engine and then the fuel that the engine don't need goes back to the tank in the other side. This return sets up a flow to the delivery side. For this to work the flow back to the tank should be good with no air in it so the first check should be to look at the clear pipe that returns the fuel for air bubbles. This problem can start after a filter change. Hopefully it will turn out to be something simple but can end up with a faulty high pressure pump as was the case in another thread

 

[paresh]

Thanks for the reply.

From the explanation above, I now understand how the fuel systems from tank to engine andthen back to tank now works.

I too was following the other thread where the owner of a W203 had a similar problem where the engine used to cut out at around half a tankful. The culprit turned out to be the high pressure fuel pump and if I recall correctly, the damage was caused after installing a new fuel filter. The advice when installing a new fuel filter is to make sure that the new filter is flooded/filled with fuel when installing and that the fuel tank is as full as possible.

I have only had the car for a couple of months and haven't changed the fuel filter. The previous owner may have had the filter changed during a service as it looks fairly new.

But I can recall when I took the vehicle for a test drive (before buying it) that the fuel guage was below a quarter of a tank and almost on reserve. I have spoken to the previous owner and he says that he had never had this problem whilst he owned the car. I believe him as I saw the fuel gauge showing less than a quarter tank! It doesn't go below a quarter tank now - the engine cuts out before it gets that low!!

142TPL - I would be grateful if you would help me identify the clear fuel return pipe so that I can check it for air bubbles.

 

[142 TPL]

It's the one that runs along the top of the engine front to back with a black plastic sleeve , on mine there is a join in the sleeve so that you can slde it back and watch the fuel go by it runs along near the fuel rail

 

[paresh]

Thanks for your reply 142TPL

I'll have a look today when I get a few spare minutes.

I've been having a think and was wondering that if there was air in the flow back to the tank then the engine cutting out problem should happen at anytime regardless of the amount of fuel in the tank. The engine only cuts out when there is around a quarter tank of fuel left.

Or maybe when the tank gets to a quarter full then air is being introduced in the fuel system somewhere and this is causing the engine to cut out. But then if this was the case, why would the engine start and run normally when I fill the tank with the gallon of diesel I carry with me? Surely one gallon of fuel introduced into the tank cannot stop air being drawn into the system (assuming that this was the cause of the engine cutting out).

Anybody else have any other suggestions that I could maybe follow?




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[142 TPL]

What can happen is the air is only introduced to the return so that the fuel coming in is fine and the pressure in the rail is fine but the pipe going back draws air and in turn does not create the right flow to get the fuel from one side of the tank to the other. The high pressure pump is infact two pumps one to pressurise the system and one to return the fuel at the correct flow. If you have an air leak on the return this will cause the fuel not to transfer over in the tank and not affect the running until you use up the fuel in the one sideof the tank

 

[paresh]

Hi all

Well I finally had a chance to check the return pipe to see if there were any air bubbles in the fuel being returned back to the tank. I had a good look for a few minutes but could not see any air bubbles. The fuel seemed to be flowing quite consistently.

If there are no bubbles in the return pipe then does this mean that the high pressure fuel pump may be faulty? I suspect that may be.

From reading other posts in this and other forums the evidence points to a faulty high pressure pump.

Any advice would be gratefully received.

 

[advent77]

Hi all

Well I finally had a chance to check the return pipe to see if there were any air bubbles in the fuel being returned back to the tank. I had a good look for a few minutes but could not see any air bubbles. The fuel seemed to be flowing quite consistently.

If there are no bubbles in the return pipe then does this mean that the high pressure fuel pump may be faulty? I suspect that may be.

From reading other posts in this and other forums the evidence points to a faulty high pressure pump.

Any advice would be gratefully received.

Hi paresh
do u perhaps recall how u solved ure issue u had with the fuel system. I'm having the same issue with my cdi270

 

[paresh]

Hi advent77

I did not solve this issue. There were no air bubbles in the the return pipe to the fuel tank so I presumed that it must have been the high pressure pump located at the front of the engine.

I did not replace the high pressure pump as it was working fine - apart from the quarter tank syndrome! There were/are no leaks from the pump so I guessed it would be better to leave it alone and put up with the problem. I carry a can of diesel with me just in case . And I always fill up the tank when it gets to just above a quarter full.

I've had no problems so far and I have never had to use the can of diesel.

Hope this helps but please do post on here if you manage to fix your problem. It would be helpful to others who may be in the same situation.