How to solve the problem of BMW 318i engine shaking and weak acceleration
(1) Fault symptoms The chassis model of this car is E46, equipped with an M43 engine. The fault symptoms are as follows: after starting the engine, the idling vibration is severe, the body vibration can be felt when sitting in the cab, and the vehicle cannot accelerate when driving.
(2) Diagnosis and maintenance From the fault symptoms, it is initially judged that there is a cylinder shortage fault. Connect the diagnostic instrument for self-diagnosis, select the “DME engine electronic servo control system ME9” item, and query the fault information. The content is shown in Table 1-3.
In order to determine whether there is a misfire failure in the relevant cylinder, check the cylinder running stability value at idle speed, see Table
1-4.
It can be seen that cylinders 2 and 4 have obvious misfires. After clearing the fault code and starting the
engine, the fault became more serious and remained the same. Check the fault information again, only
fault code 2745 is left, and the nature of the fault is current. Check the cylinder running stability value
again. The value of cylinder 2 reaches 24.35 and it is not working at all. There are usually two reasons
for cylinder shortage and misfire failure: one is poor ignition coil performance; the other is clogged
fuel
injector. The spark plug and ignition coil were replaced and tested, and the failure symptoms of
cylinder
2 did not improve. The four fuel injectors were removed for cleaning, reinstalled and then tested, but
the fault persisted. Use a stethoscope to check the working conditions of the four injectors. After
comparison, it is confirmed that the sound of the 2-cylinder injector is weak. Check the 2-cylinder
injector wiring harness connector and find a poor contact. After treatment, test run and the fault is
completely eliminated.
(3) Summary: The engine control module identifies whether there is a speed difference in the
crankshaft at a certain phase angle based on the engine speed signal, thereby determining whether a
certain cylinder is defective. To this end, the engine control module continuously monitors the time of
each sector working area corresponding to the crankshaft speed signal disc teeth, performs
corresponding calculations, and converts it into cylinder operation smoothness data. If the running
stability value of a certain cylinder gradually increases, the engine control module determines that the
cylinder has a misfire fault, sets the relevant fault code, and disables the fuel injection function
depending on the degree of the fault. Symptoms of this type of failure will not appear immediately, but
will occur gradually. Although the fault codes can be cleared, the fault symptoms cannot disappear and
require thorough inspection and elimination.