Fault analysis and troubleshooting: this car has been repaired and inspected many times before coming to the repair shop, but the problems reflected by users are always good and bad, and the fault cannot be eliminated. So we re-certified the fault phenomenon, and found that in addition to the above-mentioned fault phenomenon, there is a special phenomenon: if the start is smooth, the refueling and idling conditions are normal; If it is very difficult to start, the working conditions such as acceleration and idle speed are not good.
According to these phenomena, the author thinks that the reason may be on the ignition line, but in order to prevent oil circuit failure, the oil pressure system was quickly checked first. The method is: simulate the fault state, put forward gear and brake. At this time, the other foot lightly steps on the accelerator, which is similar to doing a stall test. Because of the increased engine load, it is easy to appear the phenomenon of seat violation. Connect the oil pressure gauge from the oil pressure test port, and the oil pressure measured when the engine is seated is 290-320KPA, which fully meets the technical requirements. Through this test, the causes of gasoline pump and oil pressure regulator can be basically ruled out. Its maintenance should focus on the ignition system.
According to the feedback from users, this car is a second-hand car and has had a traffic accident. Disassemble the engine during sheet metal forming, and you won't have this problem when you buy a car. After driving 65,438+00,000 km, idling instability and seat violations caused by refueling began to appear. I changed the spark plug and high-voltage wire, but it has not been solved. Imagine that spark plugs and high-voltage lines are only entertainment parts of the ignition circuit, not the whole ignition system. Therefore, the voltage and waveform of the ignition secondary electrode are checked by an oscilloscope. The test results show that no matter which cylinder fails, there is a fire phenomenon. But when there is no fault, the ignition waveform of each cylinder is normal. According to conventional analysis, it is impossible that six spark plugs or high-voltage lines can't break down and ignite at the same time, and the fault should appear in a general component. This car is directly ignited by three ignition coils in parallel, so the possibility of ignition coil failure is not great.
At this time, I personally consider whether the 24x crankshaft position sensor (as shown in figure 1), 3x crankshaft position sensor (as shown in figure 2) and camshaft position sensor sometimes lose signals, which makes the electronic control computer ECM unable to drive the negative electrode of the ignition coil. In addition, the crankshaft position sensor is installed at the front of the engine. Was the engine overhauled in the event of a traffic accident (the crankshaft pulley was removed and the timing gear cover was replaced)? So, is the clearance between the crankshaft position sensor and the induction gear ring appropriate? Because there is only a gap of 0.5 mm between the sensor and the gear ring, if it is too small or too large, it is easy to lose the speed signal. So the crankshaft position sensor was reassembled, and the 3x crankshaft position sensor and O-ring were replaced, so that the iron filings on the sensor head were removed. After loading, the fault still exists. Then the crankshaft position sensor and camshaft sensor were replaced, but the problem still could not be solved.
Figure 1 3X Crankshaft Position Sensor Figure 2 3X Crankshaft Position Sensor Because Shanghai Buick is a new model in China, the incidence rate is not too high. By the way, the working principle of 3x and 24x crankshaft position sensors is introduced. The 3x crankshaft position sensor is a Hall effect switch, which is close to the crankshaft. A concentric ring (with an opening) is installed behind the crankshaft balance shaft, and there are seven grooves on the ring, of which the first six grooves are 60 degrees apart, and the seventh groove is separated from the sixth groove by 10 degrees. When the concentric ring rotates with the crankshaft, the magnetic field reaches the 3x "Hall effect" switch through the groove with a certain gap on the ring. When the ignition computer is grounded to the 3x signal circuit, the signal circuit is energized. When the magnetic field is blocked by the concentric ring, the "Hall effect" switch disconnects the ground of the 3x signal circuit, thus closing the signal circuit. The ignition computer judges the position of crankshaft through 3x "on-off" pulse signal, which is the basis for ECM to calculate ignition timing.
The 24x crankshaft position sensor signal is used to accurately calculate the engine speed. The working principle of the sensor is the same as that of the 3X crankshaft position sensor. The difference is that there are 24 evenly distributed grooves on the interrupt ring. The 24x crankshaft position sensor ("Hall effect" switch) generates 24 "on and off" pulse signals per crankshaft rotation 1.
So far, the only cause of the failure seems to be the wiring and engine computer. Could it be that the computer ECM made a mistake and did not give the correct instructions, which led to the ignition disorder? Because similar vehicles that have been repaired before have found this situation, they are tested with an oscilloscope (if there is no oscilloscope, a small test lamp can be used instead. The method is to connect one end of the test lamp to the live wire of the battery, and the other end pierces the negative wire of the ignition coil to be tested. After starting the engine or running the engine, the test light should flash frequently). If the waveform has a large pulse width or the flashing time of the test lamp is different, it means that this line or computer instruction is faulty.
Through testing, it is found that all three wires of the negative electrode of the ignition coil have irregular interval stroboscopic flashes, and abnormal stroboscopic flashes will be accompanied by pathological failures. Maybe there is something wrong with the engine control module. So find a piece of the same ECM to replace, the fault remains, and there is still no possibility of eliminating it.
Where will the fault occur? In order to determine the work I have overhauled, the author measured all the circuits of the crankshaft and camshaft position sensors with a multimeter, simulated many situations and confirmed that the circuits were normal.
In the case of no progress in maintenance, the crankshaft and camshaft position sensors were replaced again, but this time a valuable clue was found: a piece of iron filings was adsorbed on the magnetic head of the 24x crankshaft position sensor! In addition, there is a strange phenomenon when doing fault auscultation, that is, there is abnormal noise in the front of the engine, which is similar to metal knocking. When knocking occurs, the engine works unsteadily and the acceleration is weak. Both iron filings and knocking sound appear in the front of the engine. Is the interruption ring on the crankshaft pulley damaged?
If the crankshaft pulley assembly is really damaged, it will definitely lead to poor fuel injection and inaccurate fuel injection control signal. Check with an oscilloscope, it is true. Then remove the negative electrode of the battery, remove the serpentine belt from the pulley, unscrew the connecting bolt between the balance shaft and the crankshaft, and remove the crankshaft pulley with special tools (as shown in Figure 3). A very strange phenomenon appeared. The broken ring of groove 24 and the fixing rivet of crankshaft pulley are loose, and the central eye hole of the connection is enlarged by about 1mm, so the two concentric circles cannot be fixed together. Only the outer baffle and bolts make the two circles move circularly in a plane. However, the two concentric circles move relative to each other due to different forces, which leads to the fact that the crankshaft position sensor cannot correctly sense the real position of the crankshaft, thus leading to confusion between ignition and fuel injection. After replacing the crankshaft pulley assembly, the fault was eliminated. The reason is that the special tool was not used when replacing the engine timing cover, and the crankshaft pulley was forcibly pulled and pried. Therefore, it is easy for maintenance workers to cause unexpected failures, which is worth learning by maintenance personnel.
Guangzhou Honda Accord 7230 has weak acceleration, unstable idle speed and sometimes flameout.
Symptoms: A Guangzhou Honda Accord 7230 car with a mileage of 3000km. After the cold car starts running for 30-35 km, the engine fault light is on, the acceleration is weak, the idle speed is unstable, and sometimes the engine stalls. After the hot car starts, the engine fault light will light up after driving with the heating on 15-20km. Turn on the air conditioner (A/C) after the hot car starts. If the air outlet opens downward to release air, the engine fault light will light up after driving for 35-40km. Maintenance record: after the engine fault light is turned on for the first time, it will be repaired in the factory. The service technician uses the engine detector to measure the fault as "bad signal of the signal rotor in the distributor". According to the analysis requirements of the maintenance manual, the technicians checked the line and the results were good. There is no problem in checking the output signal of grounding wire and distributor. Later, it was suspected that the performance of the distributor was unstable after being heated, so the technicians replaced the distributor assembly, cleared the fault code and started the trial operation. When the vehicle travels 40km, the fault phenomenon reappears. At this point, the technician began to suspect that the engine computer ECM was faulty. The reason is that the engine computer cooled down when the air conditioner was turned on (the computer was located in the middle floor), so a computer was replaced and the driving test was carried out, but the fault appeared again after driving for 30km. At this time, the technician began to doubt his technical ability and asked the technician for help.
After the technicians got together and studied the car, they agreed that there were three reasons for the failure: first, the distributor was broken, second, the computer was broken, and third, the wiring was broken. The first two technologies have been completed, and the third one should replace the engine wiring harness. Technicians instruct technicians to remove the engine wiring harness and check them one by one. No damage is found, the joints are intact and there is no corrosion or looseness. All connectors are inserted in place and connected well. In order to accurately judge whether it is a wiring harness problem or a new wiring harness debugging, the fault still exists.
Helpless, the technician reported the fault. Honda professional technicians traveled thousands of miles to further test and verify the vehicle, and finally thought that the mechanical part of the engine had failed, resulting in poor distributor signal. After inspection, the mechanical fit and timing belt are correct, and the conclusion of replacing the new engine is made.
Troubleshooting: After careful inspection, the author replaced a generator and eliminated the fault.
Misunderstanding analysis:
① The analysis of the fault causes of poor distributor signals cannot be determined only by fault codes, and waveform analysis should be used to find out the real signal waveform (preferably taken from the computer input) and the waveform change when the fault occurs.
② It is often thought that bad signals refer to sensors, but some interference signals synchronized with signals are often ignored, such as high-voltage ignition failure and generator failure.
(3) Misjudge the computer fault as changing with the temperature (the mileage of this car is lengthened after the fault is directly blown and cooled).
(4) The synchronous belt fault will cause the signal to be out of sync, but it will not change the fault reappearance time with the computer temperature.
Failure cause analysis:
After the car broke down, technicians checked the charging voltage, which was within the standard range: idle speed 12.8- 13.2 V and variable speed 1500 r/min. However, the generator full load test was not carried out. That is, turn on all electrical appliances in the car, such as headlights, small lights, defrosters, air conditioners, and the highest speed gear of blowers. Due to the damage of a group of rectifier diodes of this generator, the output waveform of the generator diverges (Figure 2), which leads to serious pulsation of peak voltage and current, which makes the voltage at both ends of the battery have pulsation interference, and the computer ground (battery negative electrode) potential also has pulsation interference. When the amplitude of this interference pulse is greater than 0.7V, the computer mistakenly thinks that the distributor signal is lost, lights the fault lamp, remembers the fault code, and enters the standby program to work, thus causing the failure of poor acceleration and unstable idle speed of the engine.