Mercedes Benz CLK 220 CDI 2003 - Non start, fuel related fault - Fixed #
Posted by Neil Webb on May 1, 2009, 7:44 am
Year of Manufacture *: 2003 Engine Code or Type *: 220cdi
Hi guys, Some of you may have come across this before, if not this is one to remember. Vehicle presented to us as a non runner, previously it had broken down on the road without warning and was then recovered to another garage who fitted a new set of common rail injectors.( that is all i know of their involvement other than seeing their invoice ) We did a low pressure and flow check which revealed no fuel being delivered. Next we checked the tank contents to find one half of the diesel tank full one half empty ( saddle type tank ) no electric pumps on this model just a small gear driven pump on the front of the engine. We examined the pipe work, pick up and return chambers in the tank but could not really see any problem. After some research into how the system worked the problem was revealed.
The fuel is drawn from the side of the tank that was empty through a pipe into a chamber in the (full) side of the tank and on to the low pressure pump on the engine and then to the high pressure pump. The cambox pressure in the high pressure pump returns fuel at a critical pressure to the side of the tank which was full, and through a venturi creating a syphon effect thus drawing fuel from the ( full ) side of the tank and through a pipe and into the ( empty ) side of the tank.
So, after checking the flow in the return line it was obvious that there was not enough pressure and flow to create the syphon effect thus balancing the tank contents. We fitted a new high pressure pump which cured the problem. I should stress that the performance of the vehicle seemed unaffected as we ran the vehicle on an independent fuel supply before fitting the new high pressure pump.
I hope this may save someone some time in future. Please feel free to comment if i have described any thing wrongly as information is difficult to come by and thats the best i can do other than say the car is fixed. Neil.