MIL on. Fault code stored:
P008B – Low Pressure Fuel Circuit: Fuel Pressure Higher than the Reference Value
The fuel low-pressure can be checked via the engine control unit parameter measurements but to rule out that the low-pressure measures incorrectly, it is a good idea to simultaneously fit a manometer on the low-pressure circuit.
Please note: The pressure shown in parameter measurements is displayed including atmospheric pressure. This means that if 5 bars are displayed in parameter measurements, it is equivalent to 4 bars on the manometer.
In case of a flawless low-pressure circuit, parameter measurements will show approx. 5 bars in fuel low-pressure and a PWM signal of approx. 27% to control of the low-pressure pump (measured at idle).
To determine whether the too high fuel low-pressure is caused by the low-pressure or the high-pressure pump, check the fuel return flow circuit.
• Attach a container to the return hose connector in the engine compartment (pos. 1 in the photo below)
• Start the engine and let it idle for 30 exactly seconds
In a flawless engine, the return flow will be approx. 500 ml.
If the return flow is significantly under 500 ml, the fault is often due to the fact that the mechanical return flow control valve of the high-pressure pump is stuck in closed position. This valve is located internally in the high-pressure pump and cannot be replaced separately. If the return flow is approx. 500 ml or more, it is often due to a faulty low-pressure pump.