Literature review of engine common fault diagnosis and maintenance.

I'll teach you. A car 1998 is very graceful. It is difficult to start in cold weather, and sometimes it won't start.

fault diagnosis

First, judge whether the fault point is in the circuit or the oil. After investigation, the high pressure fire is normal, but there is no signal to start fuel injection, so consider whether the engine ECU receives the start signal. After investigation, it was found that the starting fuse was blown, and the fuel injection signal was normal after replacing the insurance, but it was still difficult to start. Further fault analysis shows that the oil pressure is 350kPA, which is normal. At the same time, the measured cylinder pressure is 1000(PA, normal. The fault may be caused by incorrect ignition timing. If the ignition is too late, it will lead to difficulty in starting or insufficient power, so the ignition timing is found to be biased.

Dismantling the timing chain mechanism found a wrong tooth. At this time, the analysis is that the start-up insurance is burnt out because the start-up time is too long. The wrong tooth was caused by carelessness during maintenance. Re-adjust the ignition timing, install the retest car, the cold car starts normally, with abundant power, and the fault is completely eliminated. Timing chain

A Nissan A32 plane failed to start after breaking down in the wild at night and needed first aid.

fault diagnosis

First check whether the high-pressure fire is normal, and then find that there is no fuel pressure in the oil circuit. Pull out the fuel pump plug and test. It is found that when the ignition switch is turned on, the power line has a voltage of 12V, and the negative line is poorly grounded. It seems that the grounding wire of the fuel pump is not firm under the contact of the car body or the fixing nut is corroded and rusted, which causes the fuel pump not to work normally. According to the routine maintenance procedure, the two fuel pump grounding wires located between the left and right B pillars should be cleaned and fixed, but it was in the field with poor light, and the owner wanted to leave the accident site and go home as soon as possible. There were not enough rescue and maintenance tools, so it was impossible to complete this simple but heavy maintenance work in a short time. Therefore, we can only take emergency measures, lead a long lead from the negative electrode of the battery and connect it to the negative electrode of the fuel pump, and successfully eliminate the fault with one wire.

fuel pump

* Note: The car should be repaired according to the routine maintenance procedures after returning.

A 1996 Nissan Style is equipped with VQ30DE multi-point injection engine, and the mileage is 12000km. Recently, there have been frequent symptoms of starting difficulties, and all working conditions are basically normal after starting.

fault diagnosis

The cylinder pressure was measured with a cylinder pressure gauge, and the results showed that the pressure of each cylinder was about 850kPa, which met the ignition conditions (800kPa- 1 100kPa). Instead, the fuel pressure gauge is used to detect the fuel pressure, so as to judge the oil circuit. The test shows that the fuel pressure is at idle speed, and then the pressure holding experiment is carried out. The results meet the technical requirements, and the engine mechanical and oil circuit faults can be basically eliminated, so the maintenance focus is on the electrical system.

Check the anti-theft self-checking lamp first, and turn it off within 3 seconds after starting, indicating that the anti-theft system is working normally. Read the fault code with the engine diagnostic instrument. The fault code indicates that the crankshaft position sensor (CPS) is faulty. Remove the crankshaft position sensor plug above the crankcase flywheel, and the measured resistance (between line 2 and line 3) is 5 18O (normal value is 520±50n). This sensor is Hall effect, the magnet swings back and forth at the sensing position of the sensor, the pulse voltage is above 0.6V, and the sensor should be normal. However, in order to ensure its normal operation, the replacement test was carried out, and the fault remained. At this time, the automobile fault light is on, the engine diagnostic instrument reads the fault code, and the crankshaft position sensor fault is still displayed. Focus on the signal transmission line and control unit between the sensor and the engine control unit, and carefully check the two connecting lines between the sensor and the control unit. The lines are normal. Replace the control unit, and the fault still exists after trial operation. Where is the fault point?

Considering that the crankshaft position sensor takes the flywheel as the target wheel and uses the Hall effect of its rotation to obtain the engine speed signal, an oscilloscope is connected to the crankshaft position sensor line to detect the engine speed signal. Crankshaft position sensor

Observing the waveform, it is found that the sine wave is defective in a certain period. Because the sensor is new, the basic judgment problem is probably on the flywheel.

Put down the transmission and check the flywheel carefully. As a result, there is an obvious crack at the outer end of one tooth on the flywheel ball tooth. After replacing the flywheel gear ring, the fault was completely eliminated.

A A33 made in 2000, the hot and cold car accelerates normally, and the engine is easy to stall when the hot car is idling.

fault diagnosis

According to the fault phenomenon, it is preliminarily confirmed that the idle motor is not working well. Check and clean the idle motor, throttle body and spark plug, and the fault still exists. Read the fault code with the engine diagnostic instrument. Check data flow: engine speed 750r/min, idle contact connected, engine water temperature 90 degrees Celsius, air flow 5.2 1g/s, fuel injection pulse width 4.9ms, idle motor 10- 15 step (step by step). Judging from the data flow, the signal of the air flowmeter is too large (the signal of the air flowmeter should be 2.5q/s-3.5g/s at idle speed), which leads to the mixture being too rich to stop.

Main technical parameters of Nissan Fengdu engine

VQ3DEVQ20DE engine

Engine form V-6 cylinder V-6 cylinder

Engine displacement (ml) 2988 1995

Maximum power (kw/r/min)147/6400140/6400.

Maximum torque (Nm/rev/main) 27 1/3600 179/4000.

A33 adopts hot film air flowmeter, which is easy to be polluted and damaged, resulting in abnormal engine operation. So I replaced the car with an air flowmeter and tested it. The test results show that the signal of the air flowmeter is 3.0g/s, the fuel injection pulse width is 2.5ms, and the fault phenomenon disappears.