Test Methods
1)Check the Ignition Coil
CX 70 adopts 1×2 top-mounted ignition coil supplemented with resistance-type spark plug.The causes of common faults of ignition coil are:circuit failure of primary coil,being overheated or burnt of ignition coil,shell damage caused by external force,failure of high voltage wire etc,as shown in Fig.4.23.
Fig.4.23 Damage and Aging of High Voltage Tube and Corrosion of High Pressure Spring
Main inspection and judging methods of ignition coil:
①The resistance of primary winding is measured as(0.8±12%)Ωand the resistance of secondary winding is measured as(11 ±12%) kΩ.
Fig.4.24 Resistance Inspection of Ignition Coil
②Use the diagnostic unit to do the arcing test to check the working performance of ignition coil and spark plug.
Note:During the maintenance,“Short Circuit Fire Trial Method”is not allowed to test the ignition function to avoid damaging the electronic controller.
③When the key is in“ON”position,the voltage of primary coil power source is measured as 12 V;Start the vehicle and use the light test pen to check whether the ignition impulse signal of primary coil is flickering or not.
④The oscilloscope measures and analyses the ignition impulse signal of primary coil and the reference wave shape is shown in Fig.4.25.
Fig.4.25 Primary Wave Shape Reference of Ignition
2)Check the Crankshaft Position Sensor
The working principle of CX70 crankshaft position sensor is to use the magneto-electric effects,that is,the rotation of the crankshaft will make the sensor signal wheel rotate and then the gear teeth of signal wheel will produce the cutting effect on the magnetic flux of sensor so that impulse signals with certain frequency will be caused at the both ends of sensor coil.
Fig.4.26 Crankshaft Position Sensor and the Structure of Signal Wheel
Combined with the structure and working principles of crankshaft position sensor,we can use the following methods to make a quick judgment:
①When the engine can’t be started,connect it with the engine diagnostic unit and start the motor to see whether the rotation parameters are normal or not.
②(Dismantle the joint)Turn the digital universal meter to the ohms range and set the rated resistance of sensor coil(860±10%) Ωat 20 °C.
③(Install the joint)Switch the digital universal meter to direct current voltage,use the red-black probe to connect with the two pins of the sensor respectively and start the engine.At this moment,there should be voltage output.
④Dismantle the sensor and use the simulation method.Wave the metal on the top of the sensor constantly and there should be voltage signals.
⑤The wave shape of sensor signals obtained by the oscilloscope is shown as below and the frequency and amplitude vary with the rotation speed.(https://www.daowen.com)
Fig.4.27 Reference Wave Shape of Crankshaft Position Sensor Signals
3)Camshaft Position Sensor
CX camshaft sensor is Hall-effect speed sensor,whose signal output has the characteristic of on-off and the supply voltage is 5V.
Fig.4.28 Camshaft Position Sensor and the Structure of Signal Wheel
The inspection methods of camshaft position sensor:
①Dismantle the phase sensor,connect the joint and turn the key,then make the chip end of sensor get close to and leave the conductive metal plane(such as engine hood cover)and at this moment,use the universal meter to check whether the sensor signal voltage changes.
②The wave shape of sensor signals obtained by the oscilloscope is shown as below and the frequency varies with the rotation speed.
Fig.4.29 Variation Pattern of Camshaft Position Sensor Signals
Note:After dismantling clean the installation position surface to make sure that there is no greasy dirt;when installing,only press-in method is used and knocking with any tool is prohibited.
4)Water Temperature Sensor
Water temperature sensor is the thermal resistance of NTC,and the resistance value reduces with the rising of temperature.When dismantling the sensor,no operation under the heating car is permitted and make sure that the sensor is completely screwed in and no cooling liquid is leaked when installing.
The inspection methods of water temperature sensor:
①Measure the resistance values under different temperatures and the temperature and the corresponding resistance reference value are shown in Table 4.5.
Table 4.5 Temperature and the Corresponding Resistance Reference Value
②Use the diagnostic unit to read the temperature parameters and sensor’s signal voltage in the snapshot.
5)Detonation Sensor
Detonation sensor is usually installed on the cylinder body among 2-3 cylinders and no washer is used during the installation process.The metal surface of the sensor must be pressed on the cylinder block and the bolt tightening moment is(20±5) N·m.The common fault reason is that various oils are exposed to the sensor,causing corrosion to the sensor.
Inspection methods of detonation sensor:
①Check the resistance between the two signal wires of the sensor,which should be 4-5 MΩunder the normal temperature;the insulation resistance between shielding line and the metal part of sensor is above 5 MΩ.
②Use the little hammer to tap the sensor and then adjust the universal meter to millivolt and at this moment,there should be voltage signal.