How to deal with the problem of difficult starting of BMW 318i
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(1) Fault symptoms The chassis model of this car is E46, equipped with an N46 engine. The fault
symptoms are as follows: After parking the vehicle for a long time, the starter needs to be started more
than twice before the engine can run. If it starts immediately after turning off the engine, start the
engine once and you can start the car.
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(2) Diagnosis and maintenance: Confirm the fault symptoms. After parking the vehicle for 10 minutes,
start the engine. The engine can start, but the speed drops rapidly and stalls after starting. Then it
started
again and the engine finally started running. Use the diagnostic tool to conduct self-diagnosis and check
the fault information of the engine system. There is no fault code. Checked the fuel pressure, ignition
strength and intake manifold sealing, and found no abnormalities. Measure the cylinder pressure and
find that the pressure in each cylinder is normal. Looking at the engine’s operating data, the intake
valve
lift is 9.58mm, which is close to the maximum value of the control volume. At this time, the intake
manifold pressure is 53kPa, which is significantly lower than the atmospheric pressure of 100kPa,
indicating that the electronic throttle valve has implemented throttling control and the engine system
has activated emergency mode. The engine is equipped with an electronic valve control system. Under
normal circumstances, the cylinder air intake volume is controlled by adjusting the intake valve lift,
rather than by the electronic throttle. The electronic throttle is only used during starting conditions and
emergencies. It plays a throttling role in mode. Therefore, when the engine is running, the intake
manifold pressure should be the same as atmospheric pressure. The reasons that cause the engine
system to activate emergency mode are as follows. Turn off the ignition switch and turn it on after 10
minutes. Observe the engine’s working data. The intake valve lift is 1.48mm and the throttle valve
opening is 18%. This is normal. When the engine is started, the intake valve lift drops rapidly from the
original 1.48mm to 0.30mm. At this time, the engine shakes violently until it stalls. When the engine is
started again, the intake valve lift quickly drops from the original 1.48mm to 0.30mm, and then rises to
9.58mm, and the engine starts running. The throttle opening is reduced from 18% to 3%, and the
engine system enters emergency mode. The 0.30mm intake valve lift is not enough to get the engine
started. Analyzing the reasons, if there is too much carbon deposit on the intake valve, the valve
operation will be affected, making it difficult to achieve the predetermined lift, and the engine will stall
due to too little air intake. In order to verify this inference, the learning value of the engine control
module is cleared, and then the engine is started, and the intake valve lift is reduced from 1.48mm to
0.62mm and remains unchanged, and the idle speed remains stable, indicating that the previous
inference is correct. Keep engine speed at 2500r/min, use carbon removal agent to clean the air intake
system. After completion, initialize the electronic valve control system and test drive. The fault
symptoms disappear and the maintenance work is completed.
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(3) Summary: There is too much carbon deposit on the back of the intake valve, which causes the
intake valve lift to be blocked and the engine stalls when it is first started. Afterwards, in order to
enable the engine to start successfully, the engine control module enabled the emergency mode and
used the electronic throttle to control the air intake volume instead of controlling the air intake volume
through the intake valve lift. Therefore, the engine was able to run after two starts. During
maintenance,
pay attention to the engine’s air intake control method, analyze the cause by viewing the data flow, and
find the fault point.