Mercedes-Benz W212 low fuel pressure and the fuel metering valve
The W212 CDI fuel pressure is too low or a fault code points to pressure, what can be the cause?
The cause can be the high-pressure pump's fuel metering valve, the filter or the injectors. The fault is often in the injectors, which leak pressure into the return line. The injectors' correction values and return leakage should be checked before replacing parts.
How are leaking injectors told apart from the fuel metering valve?
Injector return leakage is measured with a diagnostic tool and measuring hoses; not all workshops can do it. Bubbling in the tank can indicate that the injectors let pressure back. The fault may only show on a road test, not at idle.
What is involved in a fuel metering valve fault?
A faulty valve can prevent starting or cause a warning light and limited power. The valve is in the high-pressure pump. Check the wires and connectors first, because poor contact causes the same symptoms. Replacement needs several seals, so have a workshop do it.
What should be done if the fuel is contaminated or the system has air in it?
Water or sludge in the tank requires draining and cleaning the tank, and the lines, pump, rail, injectors and filter are checked or replaced. Replacing only the filter is not enough. After the service the system is bled according to the instructions.