Step 1: use the decoder to read the fault code. The fault code is p01e8: the rail pressure is lower than the first limit under the condition of small opening of the metering unit. Since the report is a fault in the measurement unit, it is natural to check the measurement unit first.
Step 2: check the fuel metering unit and harness. Unplug the wire of fuel metering unit, and the resistance of A04 and A05 is 3 ohms; The voltage of key door at no, A04 terminal is 25V, and the voltage of harness at A05 terminal is 3V; After connecting the upper harness, the measured voltage at A04 terminal is 25V and that at A05 terminal is 24V Data Flow.
Through inspection, the voltage value and resistance value of the fuel metering unit are normal. And check the fuel metering unit and find that there is no jamming, wear and other phenomena Data Flow!
Step 3: since there is no problem with the fuel metering unit, it should be the fault of low rail pressure. Therefore, the decoder is used to read the data stream of rail pressure. When taking a taxi, the actual rail pressure can only reach 170bar, and the rail pressure is unstable. In addition, the engine can only reach 200. Then there is no doubt that it is the fault of low rail pressure Data Flow.
Step 4: DC the low-pressure oil circuit, disconnect the oil-water separator and diesel filter, DC the oil inlet and return of the low-pressure oil circuit with a transparent tube, start the engine, and the engine still doesn’t start. Check the fuel return volume of the fuel injector and the whole vehicle. The fuel return volume of the fuel injector is 0, while the fuel return volume of the oil pump is very large.
Step 5: it is preliminarily suspected that the overflow valve of the oil pump is damaged. Check that the fuel injection pump has little oil output. Block the return oil of the oil pump and the engine can start. It is considered that the overflow valve is damaged. Replace the overflow valve and the problem is solved Data Flow.
The car obviously took a detour during maintenance. Although there is a fuel metering unit in the fault code, it actually refers to rail pressure. Although it is also necessary to check the metering unit, it is actually the fault of low rail pressure. You should directly check the data flow to see whether there is a problem in the oil circuit. So when we check the fault code, we must make a good analysis and think about it ourselves, which can save a lot of effort.