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1 When testing the ignition high voltage line, a dedicated test probe must be used. The oscilloscope probe cannot be directly connected to the ignition secondary circuit. 2 When using a car oscilloscope, be careful to keep away from heat sources, such as exhaust pipes, catalytic converters, etc. If the temperature is too high, it will damage the instrument. 3 car oscilloscope should pay attention to let the test line leave the rotating parts such as fan blades and tape as much as possible. 4 When testing, confirm that the support of the engine compartment cover is good, to prevent the engine compartment cover from falling automatically when it hurts the head or damage the car oscilloscope. In the 5-way test, do not place the car oscilloscope on top of the instrument panel. It is best to test it in your hand.
2. Signal frequency and time base selection
The purpose of the time base/frequency table in an oscilloscope is to select the time base or judge the frequency of the displayed waveform based on the signal frequency. The time base/frequency table can be used to determine the signal frequency by calculating the number of times the waveform is displayed on the screen (1~5 times). The first column on the left side of the time base/frequency table is the determined frequency. Number, other columns are the current time base.
3. Oscilloscope settings
When testing an unknown signal with an oscilloscope, how to set up the oscilloscope is quite complicated. When using a car oscilloscope to capture waveforms, if you master the basic methods of setting up an oscilloscope, you can help technicians understand and master the essentials of waveform analysis.
(1) Setting items
In order to display a waveform, the oscilloscope must be set as follows: 1 voltage ratio. 2 time base. 3 Trigger level (You can also set the trigger mode to “Autoâ€). 4 coupling mode (AC, DC or GND ground).
(2) Setting essentials
Pay attention to the following items during the setting process: 1 When the waveform displayed can be clearly seen by the automatic setting function (AUTORANGE), you can use the manual setting (MANUAL) to further fine-tune. 2 If you still can't see the clear waveform on the display, you can estimate the voltage ratio and trigger level according to the inference, and do not set the time base first. 3 Use a digital multimeter to measure the signal voltage and set the voltage ratio according to the measured voltage. 4 Set the trigger level to more than half of the signal voltage. After setting the voltage ratio and trigger level, the only time that is not set is the time base. 5 At this time, the time base is manually set, and most signals should be between 1 ms and 1 s. The 6 time base/frequency table can be used to help select the time base. You can first measure the signal frequency with the swimming cursor on the car oscilloscope, then determine the number of turns (number of turns) of the desired display waveform, and then find the signal from the table. The intersection of the frequency and the number of turns (number of turns), which is to determine the time base.
(3) Operation when the waveform cannot be captured
When the waveform cannot be captured, the following operations are required: 1 Confirm that the trigger mode is in “AUTO†mode, if the car oscilloscope may not trigger in “Auto†mode. 2 Confirm that the screen display of the car oscilloscope is not in the HOLD state. If the screen has been frozen, press the release button. 3 Check if the signal really exists. You can check the voltage with a multimeter first. If you are sure that the signal is present, you can check the connection between the test leads and the post by not using the car oscilloscope and the multimeter. 4 Confirm that the coupling mode is not in “GND†(GND) mode. If it is in “Ground†mode, no signal can enter. 5 Confirm that the trigger source is defined on the selected channel. Adjustment maintenance
After a series of inspections, after finding the root cause of the fault, it is necessary to take corresponding maintenance measures to repair or adjust the fault location. After the sensor, actuator, circuit or related parts are properly repaired or replaced, the source of the fault disappears and the car is ready for normal operation.
Test run
At the end of the EFI engine repair, a completion inspection is required. The test of the test is the last maintenance step, and the test run when the symptoms are confirmed before is basically the same in the method and method, but the purpose of the two is not the same. The test run at the time of symptom confirmation is to find the source of the fault or to reproduce the fault. The commissioning test at the time of completion is to confirm whether the fault has been eliminated. During the acceptance process, the results of the vehicle repair are checked by the running of the vehicle or the operation of the engine, and the operation of the repaired or replaced parts is judged by simulating the original fault environment and the like. If a defect is found, it is necessary to take remedial action in time or to repair it again.
The inspection after the road test should actually carry out a comprehensive and meticulous inspection of the automobile engine. If no abnormality is found, the handover procedure can be completed, and the maintenance process of the EFI engine is basically completed.
Professional analysis of electronically controlled engine diagnostic testing
1. Precautions for use