In the case of the gasoline engine:
• Ignition system
When the ignition spark is weak or has no spark, the DTC relating to the ignition signal or relevant area is not displayed. As a result, the malfunction is not judged to be in the ignition primary system but in the ignition secondary system.
• Fuel systems
Judge whether the fuel pressure exists or not, the injector operates or not.
When the fuel pressure does not exist, the malfunction can be judged to be in the fuel pump and relevant area.
• Compression system
The drop in compression pressure causes difficulty in starting the engine. In this case, before the engine starting difficulty occurs, a
malfunction is caused by poor idling or a malfunction caused by insufficient power.
In the case of the diesel engine:
• Glow system
When the malfunction is in the glow system, the intake air temperature does not sufficiently rise. Therefore, the engine might not
start or may take longer time to start.
• Fuel system
When there is difficulty in starting the engine due to insufficient fuel supply, it is difficult to consider that the malfunction occurs in more than two cylinders at the same time. This is because the malfunction cause is likely to be in the parts through which the fuel is passed after its delivery, such as the injection nozzle and delivery pipe. So, these parts are not the main cause of the malfunction. Therefore, systematically inspect the parts to the injection pump and narrow down the cause of the malfunction.
• Compression system
In a diesel engine, fuel is not ignited unless it is adequately compressed, that is the engine does not start. In “The three elements inspection,” inspect the compression and judge whether the sucked air is adequately compressed or not. It is important to strongly consider the case where the malfunction of the compression system causing difficulty in starting the engine does not occur when only one cylinder fails, but when more than one cylinder fails at the same time.
7. Narrow down the malfunction based on the problem symptoms
Narrow down the cause of the malfunction based on the symptoms that “takes time to start the engine” and the situation that “difficulty in starting the engine” occurs. If the symptom is serious, the engine may not start even if there are no differences in the cause. It is important to supply the appropriate A/F ratio to start the engine. The A/F ratio greatly affects the engine’s startability, so establish the priority of the causes that affect the A/F ratio depending on the malfunction occurrence.
Judge A/F Ratio due to the Wet Condition of the Spark Plug
After cleaning the spark plug, stop the cranking before the engine starts and check the wet condition of the spark plug. If the spark plug is wet, the A/F ratio can be judged to be small. This judgement is largely affected by the engine condition prior to checking the spark plug. Even when the A/F is lean, the spark plug becomes wet due to a longer cranking time or misfire and therefore, the A/F ratio may be judged to be rich. So, it is necessary for the technician to make a judge based on this method.