1. Detection of gasoline pressure and injection state:
It is an important means to check the gasoline pressure, because the gasoline pressure directly affects the transportation and injection of gasoline. When the gasoline pressure is too high, the mixture ratio of gasoline and air is too rich, that is, the fuel injection is excessive; And the gasoline pressure is too low, which will also cause the engine to run without oil. The detection of gasoline pressure can help us find problems in electronic oil pump, pressure regulator, one-way valve, filter and oil return pipeline.
In the multi-point injection system, the corresponding accessories and pressure gauges can be installed on the pipeline joints of gasoline transportation, and the gasoline pressure can be checked by turning on the switch of the quick connector. The way to quickly detect and diagnose the pressure regulator is: when the engine is idling, if the pressure regulator works normally, the reading on the fuel pressure gauge should increase at the moment when the vacuum tube on the pressure regulator is pulled out.
When the engine cannot be started, first turn the ignition switch key to the "on" position and listen to the working sound of the gasoline pump near the gasoline tank. If not, it means that the electronic oil pump circuit is connected, or the electronic oil pump is damaged and the noise is too loud, which means that the oil in the pump is short, the oil level in the tank is low, or the oil pump is seriously worn.
In addition, there are many models, when the oil pressure is too low, the power of the electronic oil pump will be cut off through the oil pressure switch. The vibration caused by some vehicle collision accidents will also cut off the power supply of the electronic oil pump, that is, the safety self-protection device will play a role. Collision vibration cuts off the power supply of electronic oil pump, which is called collision protection switch. Cut off the power supply, stop the gasoline supply, resulting in engine oil cut-off and flameout. This device is often hidden in a certain part of the car body, and some are measured on the side of the trunk; Some are on the inside of the rear seat side panel and so on. We found the recovery switch of this safety self-protection device, and then press or pull it to make the vehicle work normally.
In the multi-point injection system, when the engine is running, we can't directly observe the gasoline injection. We can touch the syringe with our fingers and feel its working vibration. We can also use a special stethoscope to listen to the working sound of the syringe, and we can also use a multimeter to detect the power supply and pulse voltage on the line.
Note: 1. When the idle speed of all EFI engines is too low to work normally, the computer will issue instructions to compensate the idle speed to increase or decrease the speed, thus adjusting the idle speed. Therefore, when using the power balance test in the cylinder-by-cylinder flameout test, it is necessary to turn the ignition switch key to the "off" position or disconnect the command power supply of the idle air motor to prevent the idle air motor from being accidentally damaged or causing serious accidents such as fire.
2. After the high-voltage lead of the spark plug is removed and disconnected, the working duration of the ignition test shall not exceed 10~ 15 seconds. It is not recommended to remove the high-voltage ignition leads of engine transistors, because the high-voltage ignition leads are removed and the resistance is too large, which will damage the high-voltage ignition coil and the transistor ignition cross block.
3. Unburned combustible mixture is not allowed to be discharged into the exhaust pipe from the cylinder, resulting in overheating damage of combustion and three-way catalytic purification device.
2. Troubleshooting for difficult cold start:
When the cold start of EFI engine is difficult, first check whether the cold start injector works when the engine is cold. At present, many electronic control injection systems have special cold start injector devices. When the engine is cold-started, the time relay allows the cold-start injector to have enough working time to provide supplementary gasoline to help start. Most of the difficulties in cold start are caused by the failure of time relay and circuit components of the device. The multimeter can be used to detect the power supply of the power connector of the cold start injector. If there is no power supply during cold start, check related circuits and appliances. If there is power supply, clean the cold start injector.
3. Troubleshooting of idle working condition
Unstable idle speed and black smoke from engine exhaust pipe are the most common faults of EFI engine, which are often manifested as: the mixing ratio of gasoline and air does not meet the requirements, and large vacuum leaks. Idle air motor controls air flow according to computer instructions, and fuel injector controls oil quantity according to computer instructions. When the idle air motor works abnormally, the idle speed will be affected. There are also leaks in some parts, such as the leakage of the intake branch pipe and the opening of the air conditioning system, which will cause idle speed problems. When the exhaust gas leaking into the intake branch pipe causes the mixture entering the cylinder to be diluted, at this time, the computer receives the feedback from the oxygen sensor and gives the instruction to enrich the mixture, that is, the idle air motor closes the air bypass channel at idle speed, and at the same time, the failure of the oxygen sensor, the damage of the air temperature sensor, the damage of the air flowmeter, or the fault code of "ECU" may affect the idle speed. In practical work, we often encounter such problems.
In a word, apart from practical experience, the fault diagnosis and elimination of EFI engine mainly depends on the ingenious application of high-tech "engine computer detector", which can quickly diagnose and eliminate various faults, greatly improve the quality of automobile maintenance, shorten the maintenance time and create better economic benefits.