Mercedes-Benz W203 CDI starts poorly when cold
Mercedes-Benz W203 CDI: why does it start poorly when cold or crank for a long time?
The most common causes are air getting into the fuel line and too large an injector return leak. Air gets in through hardened O-rings and connectors, and the fault often shows as long cranking and the engine dying right after it starts.
Mercedes-Benz W203 CDI: how do you find an air leak in the fuel system?
Check the O-rings and connectors of the fuel hoses and lines: leak points are often wet or smell of diesel. If bubbles are visible in a clear hose, air is getting into the line. Old hoses and connectors can fall apart when removed, so renew the sealing rings at the same time.
Mercedes-Benz W203 CDI: how do you check the injector return leak?
The return leak is measured on a cold engine for about a minute into measuring hoses, which shows the differences between injectors. According to the instructions, more than 20 ml/min is a fault. A worn injector leaks too much and the injection pressure stays low, which makes cold starting difficult.
Mercedes-Benz W203 CDI: what else should be checked when the CDI will not start in frost?
Check the fuel filter, because a clogged or old filter can prevent sufficient flow in frost. The high-pressure pump seals can also leak when cold. The glow indicator lighting up alone does not tell you the glow plugs are fine, so measure them if needed.