Common fault symptoms during the operation of diesel engines include difficulty in starting, sudden flameout, weak acceleration (insufficient power), acceleration failure, abnormal smoke exhaust, abnormal coolant temperature, abnormal oil pressure, abnormal fuel consumption, abnormal sound, and fault light flashing Wait.
Due to the different electronic control systems of various models, the causes of failures are different. The diagnosis and elimination of failures should be carried out in combination with specific models and with reference to relevant technical documents.
Diesel engine won't start
1. The starter does not work
For the whole vehicle whose starter is controlled by CU, CU first checks the neutral signal when starting, and then outputs a current to drive the starter relay. After the starter relay is turned on, the battery drives the starter to start.
When checking, you should mainly check the neutral switch, starter relay, battery, parking switch under the car, etc. The specific inspection method is as follows
Check to see if it is hung in neutral.
Check the position of the under-vehicle parking switch (it should be off).
Check whether the neutral switch and wiring are in good condition, and try to use emergency start (keep the ignition switch pressed for more than 5S).
Check if the battery voltage is too low to drive the starter.
Whether the start relay and wiring are in good condition.
Check if the starter is burnt out.
Whether the ignition switch and start switch are broken.
2. The rail pressure cannot be established (the starter works normally, but cannot be started)
The common rail system has high requirements on the fuel oil circuit, and the low pressure oil circuit (fuel tank - coarse filter - fine filter - oil return) and high pressure oil circuit (high pressure oil pump - common rail - high pressure oil pipe - fuel injector) must be sealed.
① Check whether the fuel level in the fuel tank is too low. If the fuel level in the fuel tank is too low, it should be replenished in time.
② Check whether the manual pump on the coarse filter is normal, check whether there is air in the low-pressure oil circuit, and if so, it should be eliminated (sometimes the leakage of the low-pressure oil circuit is not obvious, and needs to be carefully checked).
Exhaust method (mainly exhaust the air in the coarse filter): Loosen the air bleed bolt on the coarse filter, and manually press the hand pump on the coarse filter until the oil continues to flow out of the air bleed bolt. At this time, tighten the bleed bolt and push the hand pump back to its original position.
③After the low-pressure oil circuit is exhausted, if the engine still cannot be started, there may be air in the high-pressure oil circuit, and the air in the high-pressure oil circuit needs to be removed.
Exhaust method: Loosen the high-pressure oil pipe joint of a cylinder, do not unscrew it, and use the starter to drive the diesel engine to run until the high-pressure oil pipe continues to discharge oil (it is not recommended to frequently disassemble the high-pressure oil pipe joint). At this time, tighten the high-pressure fuel pipe joint, wipe the fuel around the joint clean, and start the engine again, and it should start normally.
④ Check whether the oil circuit is unobstructed and whether the diesel filter is blocked.
Method: Loosen the outlet bolt of the fine filter, use the starter to drive the engine to run, and check whether there is fuel flowing out. If only a small amount of fuel flows out, it means that the fuel filter element is blocked, and the filter element should be replaced in time.
⑤ Check whether the initial voltage of the oil rail pressure sensor is 500mV, or check whether the oil rail pressure set by the fault diagnosis instrument is in the range of 3050MPa.
If it cannot be started normally, check whether the electrical circuit connectors are well connected. If there is no inspection equipment, you can unplug the rail pressure sensor and try to restart.
3. The injector wiring harness, sensor wiring harness, vehicle wiring harness connectors are not plugged in properly, or the wiring harness is open or short-circuited
Check the installation of the connector and check the continuity of the line with a multimeter.
4. Loss of crankshaft signal and camshaft signal
There are two speed sensors installed on the diesel engine, which are respectively the crankshaft position sensor and the cylinder judgment sensor, respectively on the outside of the flywheel housing and the high-pressure oil pump. The injection timing of electronically controlled diesel engines depends on these two sensors. When the diesel engine cannot be started, generally both signals are lost.
Possible reasons for the loss of both signals: the sensor is damaged, the wiring harness is short-circuited or disconnected; the sensor is not fixed firmly, causing the gap between the sensor and the sensing teeth to be too large or too small.
Method of exclusion:
Check if the sensor is damaged, if the wiring harness is well connected, if the sensor is loose, etc.
The installation after disassembling and assembling the high-pressure oil pump and flywheel should be carried out in strict accordance with the relevant technical documents to ensure the synchronization of signals.
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