Now with the development of automobile charges a technology, the characteristics of car failures also will be changed. It is far from the demand of test the cause of failures exactly which is only based on a simple fault code to analyse car failures. Sometimes even leads to wrong judgement and replace the wrong parts that results unnecessary economic losses.When severely leading to repeated rework, which causes a loss to the enterprise reputation. Here's some examples of common failures’ judge myths. Please all fraternities pay attention.
Failure phenomenon: engine failure light on after cool engine driving up 30~35km, speed up weaknessly, unstable idle speed and stalling sometimes. After hot car starting drive up 15~20km with opening heater, the engine fault light on. If transfer air vent to the bottom, after hot car starts driving up 35~40km with opening the air-condition(A/C), the engine failure light on.
Repair Record: After the engine failure light on for the first time, being sent to factory for repair. Maintenance technicians test it with engine tester as follows: “Bad for distributor change internal signal to embolic signal.†According to maintenance manuals for fault analysis requires, technicians conducted a line inspection with good results; Checking the JDX and the output signal of distributor are also no problem. Later, suspected the heated distributor performance is unstabe. Then technicians replaced the distributor assy. Test the cars after clearing fault codes, when cars drive to 40km, failure phenomenon appears again. At this point, the technicians began to suspect that the ECM is faulty. The reason is the air condition cooled down the engine computer(the computer is located in the middle of the floor). Then replaced a computer and made driving tests, but failure emerged once again when reached 30km. By this, technicians began to doubt their technical capacity and request technical staff to help.
After technical staffs research the cars with technicians, all agreed the failure for three reasons: first is distributor poor; second is a computer bad and the third is bad line. The first two techniques have been completed, the third should be replaced by the engine wiring harness. Technical staff guide technicians remove the engine wiring harness and exam paragraph by paragraph, found no damage and the joints is good, non-corrosion and loose. The plug connectors are in place and well-connected. In order to accurately determine whetheris a wiring harness problem, replaced the wiring harness for a new trial, but still be trouble. Helpless, technical staff will report the failure. Honda’s professional technicians drive thousands of miles for testing and verification. Finally concluded that mechanical parts of engine is failure, which results in poor signal of distributor. On examination, after mechanical support and correct breco, deciding to make a concludion of replaced engine.
Troubleshooting: After strict examination and replacing a new generator, the failure eliminated.
Misunderstanding analysis:
1, It can not only based on fault codes to analyse the failure cause of distributor’s poor signal, we should adopt waveform analysis to find out the true signal waveform( Preferably adopt from the computer input terminals department) and the waveform changes when the failure occurred.
2, We often consider poor signal is just sensor signals’ good or bad, but always neglected some interference signals with synchronization signals. Such as high-voltage ignition failure and generator failure.
3, Computer fault is miscarriage of justice for varies with temperatureblowing straight through the air after cooling, this vehicle mileage extended faults.
4, Timing breco failure can result in ASYNC signal, but not appear time to change failure along with computer’s temperature.
Failure Analysis:
The technician checked the charge voltage after this vehicle is failure. When idling, the voltage is 12.8~13.2V. When voltage is 13.2~13.8V, rotating speed is 1500r/min. They are all in standard range. But does not test the full-load generators. That is open all using electrical appliances in the vehicle, such as headlights, small lights, defroster, air condition and blower and so on. Because a group of generator-rectifier diode is damaged and the output waveform generator changes have taken place in discrimination, which resulting in severe peak voltage and current ripple. So that the both ends of battery voltage is generated pulse interference, the computer ground (batter negative) is also generated pulse interference. When the interference pulse amplitude is greater than ± 0.7V, the computer mistakenly believe that distributor signal is lost. Lit trouble light, memory fault code, enter the backup process, thus causing the engine to accelerate bad and idle instable failures.
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