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72
3.2.9 Knock
The knock sensor is a passive device, generally 2-wire, signal and ground, no external power supply is required,
and a signal will be generated when it is subjected to vibration. It can also be removed for testing. The signal can be
generated by tapping, and the signal amplitude generally does not exceed 5V; if the sensor is removed and then
reinstalled, please be careful not to cause excessive torque to avoid damage to the sensor.
There may be several reasons for knocking: the ignition angle is too advanced, too much carbon deposits in the
combustion chamber, the engine temperature is too high, the air-fuel ratio is too lean, the fuel is not clean enough,
and the fuel octane number is too low.
Use a BNC to banana cable, connect one end to channel 1 of the oscilloscope, the other end of the black plug is
grounded, and the red connector is connected to the signal line of the knock sensor with a needle.
Use ATO oscilloscope to test the knock sensor, the specific operation is shown in Figure 3-19:
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