After using a multimeter to detect the circuit, especially the power line and ground wire, it is best to use a test light with a load to verify it, so as to avoid the electrical trap of “voltage but no current”. There are as many as dozens of grounding points on the body of a modern car. These grounding points may cause poor grounding due to looseness or corrosion, causing various failures of the vehicle. However, the ground fault of the automobile circuit is relatively concealed, and the fault is not easy to find. Some grounding points are even common grounding points of multiple circuits. A bad grounding point will affect the normal operation of several systems, so we must treat it correctly. Once the fault of poor grounding is diagnosed, the grounding point should be quickly found and eliminated by referring to the relevant circuit diagram, which can often get twice the result with half the effort.Before 1967, the fuel supply system of the gasoline engine was supplied by the carburetor, which is completely different from the principle of today’s EFI engine. The carburetor uses the pressure difference before and after the throttle to absorb oil, which not only cannot accurately control the fuel supply, but also restricts the improvement of the vehicle’s power performance and environmental protection performance. Although the product names of various companies are different, they are similar in structure. The working characteristic of EFI system is “quantitative and timing” fuel injection, how much fuel the engine needs and when to inject it, which has a direct relationship with the engine speed, air flow, etc. In addition, it also involves water temperature, oil pressure, etc. Various parameters, how to deal with so many parameters, and send fuel injection instructions to the injection system? This requires the intervention of the engine control unit, and the ECU came into being.