4. Knocking sensor
(1) Knocking sensor is a vibration acceleration sensor. Mounted on engine cylinder body. Sensing element of
the sensor is a piezocrystal. Vibration of engine cylinder body is transferred to piezocrystal via mass block in the
sensor. Since pressure generated by vibration of mass block is applied to piezocrystal, it generates voltage on two
polar planes and turns vibration signal into voltage signal for output.5-122Symptom
Poor accelerationPossible cause
Various liquids, such as engine oil, cooling fluid, brake fluid, water etc
contact the sensor for a long time, which cause corrosion to the sensor. Mounting torque: 20 ± 5 N.M
Repair precautions: sensor must be fitted closely to cylinder body with its metal surface, any type of washer
is not permitted for installation. For wiring of sensor signal cables, note that do not let resonance occur to signal
cables, otherwise they might be broken. Energizing of high voltage between sensor 1 # and 2 # pins must be
avoided, otherwise piezoelectric element might be damaged.
(2) Simple measuring method:
(Remove joint) turn digital multimeter to ohm position, connect two meter pens with sensor 1 #, 2 # pin
respectively, its resistance value at room temperature should exceed 1M ohm. Turn digital multimeter to millivolt
position, use a hand hammer to tap near knocking sensor, now voltage signal output should be available.
5. Oxygen sensor
(1) Its sensing element is a ceramic tube, outside is open to exhaust, inside is open to atmosphere. When
temperature of sensing ceramic tube reaches 350°C, it will have the characteristic of solid state electrolyte. Just
utilizing this characteristic, it converts concentration difference of oxygen into electric potential difference, thus
forms electrical signal output. If mixed gas is a bit concentrated, inside and outside oxyanion concentration
difference of ceramic tube is high, electric potential difference is a bit high.
A large number of oxyanions move from inside to outside, output voltage is high (approximate 900mV); if
mixed gas is a bit thin, inside and outside oxyanion concentration difference of ceramic tube is low, electric
potential difference is low, only a small quantity of oxyanions move from inside to outside, output voltage is low
(approximate 100mV).
Possible cause
1. humid water vapor ingresses inside of sensor, temperature
changes rapidly, probe is broken.
2. oxygen sensor "is poisoned". (Pb, S, Br, Si) Symptom
Poor idle speed, poor speedup, tail gas
overproof, too high oil consumption1 2 3 4Oxygen sensor Mounting torque: 40-60 N.m
Repair precautions: it is prohibited to use cleaning fluid, oily liquid or volatile solid on oxygen sensor during
repair.
(2) Simple measuring method:
(Remove joint) turn digital multimeter to ohm position, connect
two meter pens with sensor 1# (white), 2# (white) pin respectively, its
resistance value at room temperature is 1- 6 ohm.
(Connect joint) in idle speed condition, when oxygen sensor
reaches its working temperature of 350°C, turn digital multimeter to
DC voltage position, connect two meter pens with sensor 3# (grey),Engine EFI System-Engine EFI System
