Problem: when starting the diesel engine, the crankshaft does not rotate; when starting the diesel engine, the exhaust pipe emits no smoke; when starting the diesel engine, the exhaust pipe emits white smoke.

●  Fault cause analysis:

For diesel to burn inside a diesel engine, fuel, an ignition source (the temperature generated when the piston is on the compression stroke), and combustion-supporting air are required. If a diesel engine cannot start, it is clear that the above conditions are not met.

1.The effect of the starter motor.Because the starter motor is faulty and cannot rotate, the diesel engine cannot draw in air, inject fuel, or generate compression temperature, causing the diesel engine to fail to start.

2. The effect of the fuel supply system. As can be seen from the working principle of the engine, the fuel system should inject fuel into the cylinder at the proper time and in the proper quantity, and should ensure atomization quality so that the fuel burns well; the working quality of the fuel system is mainly reflected in injection timing, injection quantity, and atomization quality.

If the fuel system has a fault, it is difficult to ensure the timing, quantity, and atomization quality of fuel injected into the cylinder, making the engine difficult to start; a common phenomenon is that there is no smoke from the exhaust pipe, usually meaning no fuel and therefore no sign of starting.

3. Poor compression in the cylinder. Cylinder compression must occur under sealed conditions, that is, when the piston moves upward from bottom dead center, the volume above the piston decreases and the pressure and temperature rise. If the components enclosing the gas in the cylinder do not seal properly.

air leakage during the compression stroke will lead to poor compression. At the end of compression, the gas pressure and temperature cannot rise, and there is no ignition source condition for fuel combustion, so the diesel injected into the cylinder cannot ignite and burn on its own, and the diesel engine cannot start.

4. The effect of ambient temperature. Diesel engine starting relies on the piston in the cylinder compressing air to generate high temperature, so that the atomized diesel injected into the cylinder can evaporate, fully mix, oxidize, and burn, pushing the piston to produce power.

If the ambient temperature is low and the engine body is cold, the heat exchange rate between the compressed air entering the cylinder and the engine body increases, causing the gas temperature in the cylinder to drop sharply. This not only worsens fuel evaporation, but also makes it difficult for the fuel to ignite and burn on its own because the ignition source condition for fuel combustion is lacking, so the engine cannot start; the unburned atomized fuel discharged from the engine appears milky white.

5. Incorrect valve timing. The opening and closing moments of the intake and exhaust valves of each engine cylinder are usually expressed by the crankshaft rotation angle, which is called valve timing.

If valve timing deteriorates with changes in the technical condition of the valve train, such as keyway or key damage causing misalignment, excessive valve clearance, wear of the cam and timing gear, torsional deformation of the camshaft and crankshaft, and so on, the original valve timing will be disrupted. In mild cases this affects engine power, and in severe cases it makes the diesel engine difficult to start.

6. Improper installation. If the timing gear marks are not aligned during maintenance, it will not only affect valve timing but also the fuel supply timing of the injection pump, causing the engine to fail to start.

7. Poor fuel quality. Water in the fuel or coolant leaking into the cylinder can prevent the engine from starting. Water entering the cylinder evaporates into steam when heated and is discharged from the engine as white smoke.

●  Diagnosis and troubleshooting:

1. If the crankshaft does not rotate when starting the engine, this indicates a starter motor fault. Diagnose and eliminate it according to the starter motor faults described in the electrical system section.

2. If there is no smoke from the exhaust pipe when starting the engine, the fuel system is faulty in most cases and should be diagnosed and eliminated according to the faults described in the fuel system section.

3. If white smoke comes from the exhaust pipe and the engine still cannot start, this indicates that the engine temperature is too low, fuel atomization is poor, or the temperature has not reached the self-ignition point and combustion cannot occur, so the engine cannot start. It should be started according to low-temperature starting procedures, meaning the engine, including the lubricating oil, should be preheated.

4. If the air temperature is normal and the exhaust pipe still emits white smoke when the engine is started, check whether there is water in the fuel or coolant leaking into the cylinder.

5. If the air temperature is normal and the diesel engine is near the end of its service life, meaning severe wear of components, or if poor engine sealing is caused by other reasons, the diesel engine cannot start because of poor compression.

Use a cylinder pressure gauge to measure cylinder pressure. If the cylinder pressure is too low, this indicates poor cylinder compression. The cause of poor compression should be identified and eliminated.

6. If the diesel engine could start before maintenance but cannot start afterward, check whether the timing gear marks are aligned correctly.

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