Engine Trouble Difficulty in Starting the Engine 1 of 2


Malfunctions regarding the engine start are roughly classified into two groups.
• The engine is not cranked properly
• The engine is cranked but does not start easily
• When devising the procedures for troubleshooting for difficulty in starting the engine, pay attention to the following points.
• In order to start the engine, adequate cranking speed and the three elements in the engine are necessary. Therefore, it is important to do a systematic inspection to discover the position of the malfunction cause
• By effectively using the diagnostic function of engine ECU, troubleshooting can proceed efficiently
1. Cranking condition inspection
(1) To start the engine, a certain cranking speed is required. In this inspection, judge whether the speed required for starting the engine is maintained or not.
(2) When the cranking speed is adequate, proceed to the troubleshooting for ignition, fuel and compression, which are referred to as the three elements in the engine.
(3) If the cranking speed is not adequate due to the malfunction in the starting system, the engine does not start even if its condition is normal.
Inspection methods
Inspect the normal engine cranking speed using a vehicle of the same model and compare it to the customer’s vehicle.
The minimum cranking speed required for starting the engine:
• 60 to 120 rpm (gasoline engine)
• 50 to 150 rpm (diesel engine)
2. Cranking condition inspection after the battery is replaced
In some cases, the cause of the malfunction gets caught in a vicious circle as in the
The engine does not start

The customer cranks for a long period of time

The battery becomes weak (discharged)

Cranking speed is inadequate
In this case, replace the battery fi rst and then inspect the cranking speed and startability.
When it is abnormal even after the battery is replaced
When adequate cranking speed is not obtained, proceed to troubleshooting starting system and engine rotational resistance inspection.
3. Engine rotational resistance inspection
When the engine is not cranked properly, the two causes, a malfunction in the starting system and the excessively large engine rotational resistance are suspected.
When the engine rotational resistance is normal
A malfunction in the starting system will be suspected. The capability of the starting system decreases and the engine is not adequately cranked.
When the engine rotational resistance is not normal
The engine rotational resistance will be excessively large. The starting system is normal but the engine rotational resistance is excessively large, causing the engine not to be adequately cranked.
4. Conformity with the result of the DTC output
Even if the DTC indicates abnormality, the malfunction that the DTC indicates is
different from the malfunction that the customer points out. Therefore, inspect the
relationship between the DTC and the problem symptom.
Normal DTC is displayed
The cause of the malfunction can be estimated in the area that has no DTC.
DTC is displayed
Check the conformity between the output result of the DTC and the problem symptom.
No DTC is displayed
When no DTC is displayed, the ECU itself can be considered not to operate properly. Therefore, the malfunction can be judged to be in the power source or the relevant area.
5. Confirm the symptoms of “difficulty in starting the engine”
The expression “difficulty in starting the engine” does not specify a cause of the malfunction. The cause is different depending on whether the initial combustion occurs or not, or if it takes a longer time but the engine starts. In this stage, the cause of the malfunction is narrowed down by understanding the specific symptoms of “difficulty in starting the engine.”
6. Three elements inspection
When neither the DTC is displayed nor the initial combustion occurs, the malfunction can be considered to be in the three elements. In “The three elements inspection,” narrow down the cause of the malfunction to either the ignition, fuel, or compression element.

Related Post