Causes of difficult starting of diesel engine
According to the working principle of the engine, the fuel system should inject fuel into the cylinder regularly and quantitatively, and ensure the atomization quality to make the fuel burn well. The working quality of the fuel system is mainly reflected in the fuel injection time, fuel injection quantity and atomization quality. If the fuel system fails, it is difficult to ensure the time, quantity and atomization quality of fuel injected into the cylinder, so it is difficult to start the engine. The common phenomenon is that the exhaust pipe is smokeless (mostly without fuel), that is, there is no sign of start-up. The reasons are mainly analyzed in the following aspects:
（1） . reasons for low-pressure oil circuit (insufficient oil supply, etc.)
1. There is no oil in the oil tank or there is insufficient oil storage, the oil pipe is cracked, the air inlet is loose, the connector is loose, water enters the fuel, the fuel filter and overflow valve are blocked, the filter screen is blocked, etc.;
2. The fuel tank switch is not opened or the air hole of the fuel tank cover is blocked;
3. The pipeline between oil tank and fuel injection pump is blocked;
4. There is an air leakage part in the pipeline from the oil tank to the oil transfer pump, so that air enters the oil circuit;
5. The filter screen of diesel engine or oil transfer pump is blocked;
6. The overflow valve of fuel injection pump is not sealed;
7. Water seeps into the oil circuit or the wrong brand of diesel oil is used.
（2） . reasons for high-pressure oil circuit:
1. The plunger coupling of fuel injection pump is worn too much and the internal leakage is large, so that the oil supply can not meet the needs of starting;
2. The fuel quantity adjusting mechanism of the fuel injection pump is stuck, so that the plunger cannot rotate or the rotation is too small;
3. Poor sealing of oil outlet valve, resulting in no oil supply or insufficient oil supply;
4. The injector needle valve cannot be opened due to carbon deposition or sintering
5. The opening pressure of injector needle valve is adjusted too high;
6. The injector orifice is blocked;
7. There is air in the high-pressure oil pipe or its joint is loose.
8. Low fuel injection pressure and poor fuel injection atomization, stuck needle valve of multi-layer fuel injection nozzle, broken regulating spring of fuel injection nozzle, etc.
（3） . other reasons:
1. Fuel injection timing is inaccurate. The reasons include wear of push rod roller and cam, damage of driving parts of fuel injection pump and improper adjustment.
2. The preheating device for low-temperature starting fails, and the temperature in the cylinder of the diesel engine is too low;
3. Oil supply time is too early or too late;
4. The compression pressure of the cylinder is too low, and the temperature and pressure at the end of compression cannot reach the temperature that makes the diesel spontaneous combustion.
5. The cylinder does not have air intake or the air intake is seriously insufficient. The reasons include serious blockage of air filter, blockage of exhaust pipe and too large valve clearance.
Troubleshooting
（1） . the oil supply of low-pressure oil circuit is not smooth.
The oil inlet and return pipelines from the oil tank of the diesel engine to the oil inlet chamber of the fuel injection pump belong to the low-pressure oil circuit. When the pipeline joint, gasket and oil pipe leak oil due to damage, the air will be blocked into the oil circuit, resulting in poor oil supply, difficult engine start, slow acceleration and other faults. In serious cases, it will automatically shut down. When the aging, deformation and impurity blockage of the oil pipe reduce the cross-sectional area of the oil, or the dirty oil is plugged into the oil filter screen and diesel filter element, it will cause insufficient oil supply and reduce the power of the engine and make it difficult to start. When checking the fault, pump the oil to a certain pressure with the hand oil pump and loosen the vent screw. If there are bubbles overflowing and the exhaust is not exhausted all the time, it indicates that the air enters the oil circuit; If there are no bubbles, but the diesel oil overflows weakly from the bleeder screw, it indicates that the oil circuit is blocked.
The troubleshooting method is to find out the damaged or aging gasket, joint or oil pipe and replace it; The prevention of such faults is to clean the oil inlet filter screen and diesel filter element frequently, check the pipeline frequently, and solve the problems in time.
（2） . the piston spring of oil transfer pump is broken.
The engine suddenly stalls during operation and cannot be started. After exhausting the air and restarting, the engine automatically stalls again after returning to normal driving for a certain distance. It is likely that the piston spring of the oil transfer pump is broken. The troubleshooting method is to unscrew the screw and replace the spring.
（3） . the check valve of the oil transfer pump is not tightly sealed.
It is difficult to start the engine after it has been shut down for a certain period of time. There are bubbles overflowing after loosening the vent screw. It is necessary to exhaust the air again before starting. This fault is mostly caused by the loose sealing of the check valve of the oil transfer pump. The inspection method is to unscrew the oil outlet screw of the oil transfer pump and fill the oil chamber of the oil outlet connector with fuel by hand. If the oil level in the connector drops quickly within 3 minutes, it indicates that the one-way seal is not good. Remove the check valve and check whether the sealing surface is intact, whether the check valve spring is broken or deformed, and whether there are particle impurities on the sealing seat surface. Grind the sealing surface and replace the check valve or check valve spring to eliminate the fault.
（4） High pressure oil pipe is blocked.
When the high-pressure oil pipe of a cylinder is blocked due to deformation or impurities, there is an obvious knocking sound at the oil pipe after starting the engine, and the engine power decreases because the cylinder cannot work normally. The inspection method is to loosen the nut at the oil inlet end of the high-pressure oil pipe cylinder by cylinder. When the knocking sound disappears after loosening a cylinder, it can be concluded that the cylinder is a faulty cylinder, and the fault can be eliminated after replacing the oil pipe.
（5） . the fuel injection nozzle coupling is stuck.
When the needle valve of the fuel injection nozzle is stuck in the closed position, there will be regular knocking sound due to the impact of the pressure wave of the fuel injection pump on the fuel injector. The judgment method is: loosen the high-pressure oil pipe connected to the fuel injector end. If the knocking sound disappears immediately, it can be determined that the needle valve of the fuel injector of this cylinder is stuck.
