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 recover its good starting performance even without replacing a new ECU, an expensive computer component.

Senior Technician of Automobile Maintenance Paper Keywords: Difficult cold start; Fuel injection pulse width; Water temperature sensor

Second, the preface of the thesis of senior automobile maintenance technician

Automobile electronically controlled fuel injection engine is the product of mechatronics, especially the control system of the engine. It 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 the whole assembly 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.

Three, senior technician of automobile maintenance thesis text

(A) senior technician of automobile maintenance paper fault phenomenon

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 starting phenomenon will greatly shorten the service life of the battery and starter.

(2) Fault detection and analysis of automobile maintenance senior technicians.

When the engine of electronically controlled fuel injection system works, the control system constantly detects the signals input by each sensor, calculates the optimal fuel injection quantity and the optimal primary circuit on 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, so as to 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) senior technician of automobile maintenance started the engine four times in a row, but there was still no sign of the car. 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.

(2) Auto Maintenance Senior Technician Thesis Unplug the central high-voltage line from the cylinder head for about 7mm, and start the engine to test the fire. The high-voltage line emits a strong blue-and-white spark, with a loud sound and constant fire. When the spark plugs of four cylinders were removed, no wetting phenomenon was found. It is normal to plug the spark plugs into the ignition wires and plug them back into the central high-voltage line to test the fire.

(3) The senior technician of automobile maintenance unplugged the fuel pump fuse, started it three times, released the fuel pressure, and measured the cylinder pressure in the cold state. The cylinder pressures of the four cylinders are 1 108kPa,110kpa,11/2kpa,1.

(4) Measure the fuel pressure. Connect the fuel pressure gauge between the gasoline filter and the oil pipeline with a tee, replace the fuel pump fuse, turn on the ignition switch, and so on. It is found that the pressure gauge reads 295kPa, and the fuel pressure does not drop when starting, which is normal compared with the standard value of 294kPa.

(5) After analyzing the above test results, senior automobile maintenance technicians found that the fuel injection pressure, spark energy and compression pressure were normal when the engine was started, and the fault may be caused by the lean mixture concentration. So remove the upper cover of the air filter, thicken it with carburetor cleaner and start it at the same time. The result is that the car can be started together, and the car can be started smoothly after repeated twice, which proves that the above judgment is correct.

So, what are the factors that affect the concentration of mixed gas? Auxiliary pneumatic AAC valve, throttle sensor, air flowmeter, water temperature sensor, etc. It is possible. However, from the analysis of fault phenomena and test results, the engine works normally after starting. The engine fault light is off again. According to the setting conditions of ECU's fault insurance system, the throttle sensor, air flow meter and water temperature sensor at least have no hard faults. The auxiliary air control AAC valve will not cause the mixture to be too lean when starting. According to the working principle of electronically controlled fuel injection system, when the engine starts, ECU will provide start-up enrichment compensation fuel injection pulse width after receiving the start-up signal, and the compensation amount depends on the detected engine temperature. The question now is whether the ECU receives the start signal when starting. Is there a problem with the water temperature sensor signal? Is the amount of fuel injection pulse width compensation provided sufficient? Refer to the circuit diagram of Bluebird U 13 SR20DE engine (see attached page), measure the No.34 pin of ECU with multimeter, and the voltage at startup is llV, which proves that the startup signal has been sent to ECU. Unplug the wiring plug of the water temperature sensor and turn on the ignition switch. The measured signal voltage is 4.9V, which is normal. At this time, the resistance of the water temperature sensor is1.4kΩ. Turn off the ignition switch, take off the battery head, unplug the wiring plug of the ECU, and measure that the water temperature sensor is connected to the pinsNo. 18 and No.2 1 of the corresponding ECU, and the conductivity is normal. Replace the wiring plug and battery head. Replace a new water temperature sensor, the measured resistance is1.5kΩ, plug in the wiring plug and start the engine, but the car still cannot be started immediately. It means that there is nothing wrong with the water temperature sensor of the car.

(6) Automobile Maintenance Senior Technician Paper Measure the fuel injection pulse width with the engine fault detector, connect the wiring, turn on the ignition switch, and click the menu to enter the fault diagnosis program. First, read the engine fault code and display "System OK". Select "Read Data Stream" to show that the current temperature is 30℃ and the fuel injection pulse width is 8.8 ms ... Because the detailed data of fuel injection pulse width at startup cannot be found, we can only use another normal vehicle of the same model to measure the data as a reference. Source: store community source text friendly reminder: This information comes from the information released by members of the forum (BB community) and can only be used as reference information, not as a basis for confirming data.