2012 Dongfeng Honda Spirior engine cylinder missing

The 2012 Dongfeng Honda Spirior, equipped with a K24Z3 engine (2.4L), has traveled about 85,000km

Fault phenomenon:
According to the owner, the engine was not restarted again after it was shut down due to water ingress, so it did not cause much damage. After repairing the water ingress part (cleaning the wiring harness plug with WD40, replacing the water-ingressed computer module, etc.), the engine ran normally, but the engine fault light occasionally lit up during the test run. The fault information was read with a diagnostic instrument, and it was found that the system had a fault code “P0301-Engine No. 1 cylinder missing”, and this fault code could be deleted, but the fault remained after another test run.

Fault analysis:
For the fault phenomenon of the vehicle, especially the fault involving the electrical part, there are five steps that must be followed during diagnosis (i.e., the “five-step diagnosis method”):

①Verify and confirm the fault;

②Analyze the schematic diagram;

③Find the fault by detecting the circuit;

④Determine the fault and repair and eliminate it;

⑤Confirm that the circuit is working properly.

According to these 5 steps, the diagnosis will not be clueless and will take fewer detours.

Step 1: Verify and confirm the fault phenomenon. There is nothing abnormal when the engine is idling, and there is no fault code or missing cylinder record. During the test drive, the engine accelerates strongly when the road conditions are good, but when the road conditions are not so good, the engine fault light will light up, which limits the power output and needs to be restarted to drive normally.

Step 2: Check and analyze the circuit diagram related to the fault phenomenon. According to the order from power supply to circuit, components and then to ground wire, determine the circuit working principle according to the current path, and determine one or several possible causes of the fault in combination with the fault phenomenon and circuit operation. Based on the principle of easy first and difficult later and the high and low frequency of faults, first check the ignition coil and spark plug. Since cylinder 1 was missing every time, the ignition coil of cylinder 1 was swapped, but the fault still existed, which proved that the ignition coil of cylinder 1 was working properly. The power supply and ground of the four ignition coils are connected in parallel, but the drive signal lines of the ignition coils are separated. After carefully checking the connection of the relevant wiring harnesses, no abnormality was found. Although the engine computer may also have a fault, the engine computer PCM cannot be replaced at will without any basis, and the water did not soak the engine computer PCM, so the factor of the engine computer PCM is not considered for the time being.

The influence of the spark plug on the engine is very critical. Remove the spark plug and observe the color of the spark plug skirt to roughly judge the working condition of the engine. The normal color should be brown. If the spark plug skirt is black, it means that the fuel mixture is too rich; if it is white, it means that the mixture is too thin. If it is white or even some white crystals appear, it may be that the engine temperature is too high. Of course, the influence of fuel quality cannot be completely ignored. Poor fuel quality can also cause abnormal color of the spark plug. It should be noted that if the spark plug is an original part and the quality is fine, but the color of the spark plug skirt is abnormal, then you need to find some reasons such as fuel mixture, rather than blindly replace the spark plug. Through the above inspection, it can be basically determined that the ignition system of the faulty vehicle is working normally.

Then check the injector. Since the injector analyzer in the store is broken, the injector was not removed for atomization and leakage testing. Turn off the ignition switch, wait for 90s, unplug the wiring harness plug of the injector, and measure the resistance of the injector to be 11Ω (Figure 5), which is within the normal range (10~13Ω). Therefore, it is preliminarily judged that the injector meets the requirements.

Fault Analysis Fault Analysis Solution:
Next, check the cylinder pressure of the engine. The specific operation method is: warm up the engine, disconnect the injector wiring harness, remove the ignition coil and spark plug, install the cylinder pressure gauge on the spark plug hole, and use the starter to drive the piston to rotate with the throttle fully open. Through measurement, it is found that the compression pressure of the No. 1 cylinder of the faulty vehicle is 12.5kgf/cm2 (1 226kPa) as shown in Figure 6, which is greater than the standard value of 9.5kgf/cm2 (930kPa) specified in the maintenance manual, and meets the requirements; and the maximum deviation of the compression pressure of the four cylinders is within 1kgf/cm2 (98kPa), which is also within the standard range.

From the above inspection results, the engine cylinder compression pressure, ignition coil, spark plug, and fuel injector of the faulty vehicle are all working normally. What is the reason for the cylinder failure? Through repeated test runs and summarizing the laws of the occurrence of faults, it is found that the engine cylinder failure seems to be related to steering. So the Honda special diagnostic computer HDS was connected and tested. After multiple test runs, it was found that when the vehicle turned left, the fault code of cylinder No. 1 would be generated, and the more intense the left turn, the more obvious the fault, but the engine fault light would not light up when turning right or driving in a straight line.

What factors caused this strange fault phenomenon? Many possibilities have been ruled out through the previous inspection steps. Could it be caused by fuel problems? After removing the fuel filter, water was found in the fuel tank.

After replacing the fuel filter and the fuel in the tank, the vehicle fault was completely eliminated.