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Home > Industry Information > Detailed Analysis of Automobile Ignition System Failure Cases (Pasate Automotive as an example)

Detailed Analysis of Automobile Ignition System Failure Cases (Pasate Automotive as an example)

2021-04-25

This article describes the Passat automotive maintenance process and analysis of ignition failures. Through the fault phenomenon of the case, the multi-directional detection of the vehicle ignition system was conducted, which was summarized into two aspects: mechanical and electrical circuits. This time the main focus is on the overhaul of the circuit, including the overhaul of control lines, sensors and ignition modules. The inspection of the circuit not only has the unit test more comprehensive analysis of the ignition waveform of the vehicle, but ultimately finds out where the fault is.

First, fault description and preliminary solution

After passing a distance of 270,000 km, a 2002 Passat had a low temperature and a hard start, and the high temperature started normally. Unsteady idle, there are signs of missing cylinders, high speed and normal. The car has been replaced with air flow meters, ignition control modules and related accessories in other auto repair plants, but the effect is not good.

1, fault diagnosis

Ask the user the conditions, time, location and other factors when the fault occurred. After preliminary analysis, the tail gas analyzer was used to detect the exhaust gas. It was found that the exhaust gas discharged by the engine exceeded the standard significantly, and the measurement results were analyzed. It was initially determined that the fault point should be in the ignition system.

The first is to use a computer to read the engine's fault code and find that there is no fault code, then read the data flow and ignition waveform to find that the high voltage of the ignition coil is low. In addition, according to the owner's description, the spark plug and the divided cylinder high-voltage line have just been replaced, and the reason for the analysis may be the ignition module and its control circuit. Because the ignition method of this vehicle belongs to the double-headed simultaneous ignition, the following dismantling and analysis are performed using a multimeter and an oscilloscope. The circuit is as shown in Figure 1 below.

Detailed Analysis of Automobile Ignition System Failure Cases (Pasate Automotive as an example)

The first is to remove the spark plug and find that there is a little white spot on the surface of the spark plug. The spark plug gap meets the technical standards of the vehicle. In addition, using the multimeter's ohm file to check the value of the sub-cylinder high-voltage line, both do not exceed 25 kilo-ohms, and also meet the technical requirements. At this point, after the routine inspection has no problems, the possible causes may be analyzed as follows: A certain cylinder does not ignite, the cylinder compression pressure is insufficient, the spark plug itself does not flash over, and the high pressure line of the sub cylinder is leaked.

Second, fault detection and analysis

Possible reasons for considering such failures at this time are mechanical, control circuits and other reasons.

2.1, mechanical failure:

(1) Cylinder pressure detection Since measuring the cylinder pressure is relatively easy to achieve, a pressure test was performed on the cylinder-by-cylinder of the vehicle and it was found that the pressure was basically the same, and no individual cylinder pressure was found to be low.

(2) Ignition Timing Detection Timing inspection of the engine was performed by using a dedicated timing reference mark, and the locking bolt of the crankshaft of the engine was turned. No timing misalignment was found.

2.2, control line failure

(1) Crankshaft position sensor sensor inspection and analysis. According to the analysis of the engine control principle, the crankshaft position sensor is one of the main control signals for ignition and fuel injection of the engine. If this signal is lost, the engine will not continue to operate. The sensor is then detected as shown in FIG.

Detailed Analysis of Automobile Ignition System Failure Cases (Pasate Automotive as an example)

1) Data flow test analysis. With the Kinder KT600, the data stream is read as the engine speed increases and decelerates. It can be seen from the data flow that the sensor is working properly.

2) Sensor resistance and harness detection.

a. Detect the resistance of the crankshaft position sensor sensor: Use the resistance of the multimeter to detect its resistance. The red pen is T2an/1 and the black pen is T2an/2. The resistance range is 1.1K-1.4K ohms.

b. Detect the on-off detection of the harness. Use a multimeter to select the buzzer file. The red pen is connected to one end of the wire. The black table pen is connected to the other end of the same wire. If the multimeter sounds, it means that there is no short circuit, but it does not mean that there is no short circuit. Short-circuit tests are also required.

c. Detection of the short-circuit detection of the harness: The red meter is connected to one end of the wire that has just been tested and the black meter is grounded. If there is a buzzer sound, it indicates that there is a short circuit, otherwise the circuit is normal.

3) Waveform detection and analysis. According to the equipment requirements, connect the power supply and signal lines to analyze the signal, as shown in Figure 3. A prominent high-tooth wave was found during the inspection. According to the working principle of this type of sensor, the possible reason is that the signal tooth plate has missing teeth, or there is a short circuit in the sensor, as shown in FIG. 3 .

Detailed Analysis of Automobile Ignition System Failure Cases (Pasate Automotive as an example)

The high gear signal is used as the ignition signal of the top dead center of a cylinder, and it is the engine cylinder signal. When the engine needs to re-identify a cylinder after the engine has been operated for a working cycle, it is necessary to determine whether it has reached the top dead center of the cylinder. If the signal is lost during operation or the signal is disturbed by the outside world, the engine cannot receive the signal normally. Due to the protection of the engine, the control unit will turn off the engine at the first time.

If two cylinder signals have appeared in one work cycle. The engine couldn't correctly judge which signal was actually needed and it would have a bad job.

(3) Ignition module and line fault detection and analysis

1) Detect the main control line of the ignition control module. Connect the T5e/1 terminal on the controller with a multimeter red pen, and ground the black test leads. Measure the power supply circuit of the control module. The voltage of this terminal should be 12V; T5e/2 terminal is the grounding terminal, namely the negative pole, should keep the grounding well, the resistance is smaller than 1 ohm.

2) Check the signal control line of the ignition module. There are three signal lines, namely green gray (T121/94-T5e/5), green white (T121/103-T5e/4), gray yellow (T121/102-T5e/3). The off and short circuit conditions. The specific detection method is to use the buzzer of the multimeter. Red and black pens are measured at both ends of the wire respectively. If the wire is not short-circuited, it will beep. Instead, open circuit. Short-circuit detection is then performed: any one of the two pens is grounded. If there is a beep, it indicates the phenomenon of disassembly and short-circuiting, and vice versa.

(4) Detection and analysis of ignition waveforms. Before detecting the ignition waveform, first clear the normal waveform and analysis, as shown in Figure 4 below.

Detailed Analysis of Automobile Ignition System Failure Cases (Pasate Automotive as an example)

Parallel waveforms and horizontal bar waveform analysis were used in the test, and finally, there was a problem with five-cylinder ignition. During the oscillation of the waveform, the five-cylinder waveform voltage is weak and the spark quality is poor. As a result, the location was re-inspected again. Finally, it was found that there was a small crack at the interface of the ignition coil and there was a leakage phenomenon.

Third, the failure summary

During the maintenance process, we will use advanced electronic equipment to conduct inspections and help us to achieve a multiplier effect. However, we sometimes lack the equipment to trust too much, and when there is no way to give a fault code, we have no idea. This time we need to start from the principle of the control system and check from the root. In the process of inspection, it is necessary to insist that: If it can be removed without dismantling, it cannot be used without instruments, and it can be simple. From the outside to the inside, they are tested from simple to complex. In the detection process, it is also necessary to use waveforms for fault analysis. Often mechanical faults can also be reflected in the circuit. Therefore, the analysis problem must be comprehensively considered from various aspects.


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