In most cases, the starting difficulties of diesel engines are generally soft faults (faults caused by non mechanical component damage, while faults caused by mechanical component damage are relatively easy to determine). Therefore, when a diesel engine experiences a difficult to start fault, the first step is to determine whether it is caused by fuel system factors or circuit system factors.

Step 1: First, ensure that the fuel system is free of air and there are no leakage points.

Step 2: Determine if the startup machine is running properly. If the starter motor is not running properly, it indicates that the malfunction may be caused by factors within the starter system itself (such as insufficient battery or other factors); Generally speaking, diesel engine start-up difficulties caused by the starting system's own factors are relatively easy to diagnose and solve. If the starting machine is running normally and the starting speed is also normal, the problem is generally not in the starting system. The following measures can be taken to further determine the fault point.

① While driving the diesel engine to rotate, use a hand pump to continuously pump oil. If the diesel engine can start at this time, it indicates that the fault is due to insufficient fuel supply in the low-pressure oil circuit system. At this point, it is possible to further investigate the cause in the low-pressure oil system (mainly by observing whether there are leakage, blockage, or insufficient preloading factors in the low-pressure oil system).

If the manual oil pump is used continuously to pump oil, and there is no improvement in the starting performance of the diesel engine, then the problem generally does not lie in the low-pressure oil circuit system; At this time, corresponding inspections should be carried out on the high-pressure fuel system (high-pressure pump, injector, common rail and its sensors), electronic control system and cylinder of the diesel engine.

② If the fuel system and starting system of a diesel engine are normal, but the diesel engine still has difficulty starting, and there are abnormal phenomena such as insufficient power, oil burning, and black smoke during the operation of the diesel engine after starting, the fault is generally inside the cylinder, valve distribution mechanism, or intake and exhaust system. The main reasons are severe cylinder wear, incorrect valve clearances, worn valve mechanisms, mechanical damage to valves, or blockages in the intake and exhaust systems. The elimination of such faults requires professional handling.

③ The following phenomena may also cause difficulties in starting diesel engines:

a. The intake pipe is blocked (not completely blocked), resulting in poor air intake.

b. The exhaust muffler and exhaust post-treatment device are blocked (not completely blocked), resulting in poor exhaust flow.

c. The failure of the phase sensor (one of the crankshaft speed sensor and camshaft position sensor) in the electronically controlled diesel engine may cause difficulties in starting the diesel engine (some models may not be able to start).

d. Individual fuel injector wiring harness faults, connector faults, or other sensor failures in electronic controlled diesel engines can all cause difficulties in starting the engine.

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