Due to errors in engine manufacturing and deterioration in car using condition (such as wear and tear of piston ring, carbon
deposit in cylinder, etc.), the real control effect of EMS (Engine Management System) will deviate from the designed ideal
condition, thereby leading to increased fuel consumption, worsened exhaust or decreased efficiency. So, an oxygen
sensor is installed to form a closed-loop control system for control of the exhaust. That is to use it to detect the instant
makeup of the mixture entering into the engine and then input the detected result into ECU. ECU continuously adjusts the
fuel injection rate according to this feedback so as to keep the fuel concentration in the mixture all the time within an ideal
range. This control method not only further increases the injection accuracy, but also controls the exhaust to ensure that
the catalytic converter has the most satisfying purification effect. To be more specific, oxygen sensor is used to detect the
oxygen concentration in the exhaust, which depends on the air-fuel ratio of the mixture. When the real fuel concentration
is higher than the theoretical fuel concentration (its air-fuel ratio is lower than 14.7:1), the exhaust contains no oxygen;
when the former is lower than the latter, the oxygen in the mixture will not be completely consumed and the exhaust
contains oxygen. The lower the fuel concentration in the mixture is, the higher the oxygen concentration in the exhaust is.
ECU adjusts the fuel injection rate according to the feedback from the oxygen sensor so as to make the fuel concentration
in the mixture closer to the theoretical air-fuel ratio; Its error rate is less than ±0.25; When the engine’s working condition
worsens, it will adopt the open-loop control method in order to avoid overheat caused by the catalytic reaction.
Fault phenomena related to oxygen sensor include unstable idling speed, high fuel consumption and excessive exhaust.
The examination method is as follows:
1. Shut off the ignition switch and remove the oxygen sensor’s plug. Use a multimeter to measure the resistance of the
oxygen sensor’s heating resistor, which should range from 1ohm to 5ohm.
2. Install the oxygen sensor’s plug and then start the engine. When the engine speed reaches 2,500r/min, use an oscillo-
graph to measure the voltage waveform between the No.6 pin (OX) of E4 and the No. 24 pin (E1) of E3 in ECU (See Fig.
276). The correct voltage waveform, whose amplitude should be more than 0.3V, is as shown in Fig. 277a. If the oxygen
sensor is damaged, the amplitude of vibration will decrease, as shown in Fig. 277b. The voltage between the above two
pins measured by a multimeter should be more than 0.3V.
3. Replace the oxygen sensor and keep the engine running at an idling speed for three minutes or so. Then, increase the
engine speed to 1,500r/min and switch on the air-conditioner. At the moment, the idling speed drift should be 1,200 r/min
or above. If there are one or more faults, the warning lamp for engine will light up about one minute after acceleration.
Here, you shall carefully examine the connections to the oxygen sensor. To use oxygen sensor needs use unleaded gaso-
line. Generally,it’s life larger then 160,000KM.
XII.Examination of Oxygen Sensor
Fig. 274 Correct tachometer connection
Fig. 275 Examine the injector’s working noi
check connector
tachometer
121
Содержание JL481Q
Страница 1: ......
Страница 9: ...5 Fig 3 Components Assembly Drawing of MR479Q MR479QA Engine ...
Страница 10: ...6 Fig 4 MR479Q MR479QA Engine and Its Power System ...
Страница 11: ...7 Fig 5 Assembly Drawing of Engine and Its Auxiliaries MR479Q MR479QA ...
Страница 12: ...8 Fig 6 Electronic Control Fuel Injection System in Engine MR479Q MR479QA ...
Страница 13: ...9 Fig 7 Front view of Engine JL481Q MR481QA ...
Страница 14: ...10 Fig 8 Sectional elevation of Engine JL481Q MR481QA ...
Страница 15: ...11 Fig 9 Electronic Control Fuel Injection System in Engine JL481Q MR481QA ...
Страница 21: ...17 Fig 13 Exterior Feature of JL481Q Engine Power Me N m Torque Pe Kw ge g kwh Fuel Consumption Ratio ...