1. Contaminated fuel: Verify engine operation with clean fuel in a temporary tank.
2. There is air in the fuel: drain the fuel and check for leaks.
3. Fuel leakage: Check the fuel pipeline, fuel connector and fuel filter for leakage.
4. The overflow valve of the fuel pump is faulty: check the overflow valve. Replace if necessary.

Fuel pump failure:

1. Check whether the fuel pump works normally.
2. Check the output pressure of the pump.
3. Replace the fuel pump if necessary.
4. Excessive valve clearance: Adjust the valve to ensure that the push rod is not bent and/or the rocker is not severely worn.
5. Incorrect timing of fuel injector pump: check the fuel injector. Replace if necessary.
6. Fuel injection pump failure: 1. Put the engine at top dead center 2. Check and adjust the fuel injection timing.