I. Summary

This paper mainly introduces a Bluebird car produced in 1994. Due to the failure of some control functions of engine ECU, it is difficult to start the car cold. By adding a circuit consisting of a water temperature sensor and a relay, the car can even restore good starting performance without replacing a new ECU, an expensive computer component.

Keywords: difficult cold start; Fuel injection pulse width; Water temperature sensor

Second, the preface

Automobile electronically controlled fuel injection engine is the product of high-tech mechatronics, especially the control system of the engine, which is equipped with multiple sensors, actuators and electronic control elements. When the control system works, various signals cross each other to control air intake, fuel injection and ignition. Once a fault occurs, the boundaries of symptoms are blurred. Moreover, it is very likely that only part of the fault will occur, and the other parts are still intact. However, the control unit is usually a whole, so it is not economical to replace components in order to eliminate local faults. Therefore, we must fully understand the structural principle of electronically controlled fuel injection engine, master the related functions, use scientific analysis methods and maintenance skills, formulate practical and economical maintenance plans, and take some simple compensation measures to make up for these functions. In order to achieve the purpose of eliminating this local fault.

Third, the text.

(A) the phenomenon of failure

There is a car called Bluebird U 13, which was built in 1994 and the engine model is SB20DE. During cold start, it takes more than ten times to get on the bus. Stepping on the accelerator at the beginning has little effect on the car, and the hot car is relatively better. After starting, the engine works normally and there is no other abnormal phenomenon. However, this difficult start-up phenomenon will greatly shorten the service life of the battery and starter.

(2) Fault detection and analysis

When the engine of electronically controlled fuel injection system is working, the control system constantly detects the signals input by each sensor, calculates the optimal fuel injection quantity and the optimal primary circuit connection time according to the algorithm set in the program, and converts them into control signals to control actuators such as fuel injectors and ignition coils, and control the fuel injection quantity and ignition advance angle. So that the engine can obtain the best working state under various working conditions.

According to the working principle of gasoline engine, in order to make the engine run smoothly, the following conditions must be met: ① The supplied mixture should meet the air-fuel ratio (concentration) required by the working condition; ② Proper cylinder compression pressure and injection pressure should be available when working; ③ There should be enough spark energy when igniting. In order to diagnose the causes of the above-mentioned vehicle failures, the following tests are conducted according to the above analysis:

(1) Start the engine four times in a row, and there is no sign of landing. Step on the accelerator to the end and continue to start it for 2 times, but there is still no sign of fire. Measured by multimeter, the battery voltage at startup is 1 1V, which is normal. When the sound detector is aimed at the fuel injector, the "click, click" sound of the needle valve can be heard when starting, and the fuel injector works normally.