Automotive Troubleshooting Engine Stall and Hesitation 1 of 2


Engine stall
There are many conditions under which engine stall occurs.
• When the engine is idling, the engine speed becomes unstable and the engine stalls.
• While the vehicle is running, when the accelerator pedal is released because there is a red traffic signal, the engine stalls.
• When accelerating or going over humps, the engine loses power and stalls. As for engine stall, reproducing the problem symptoms is difficult in most cases. In order to reproduce the symptoms during troubleshooting, it is necessary to ascertain from the customer the conditions under which engine stall occurs. After the engine stalls, difficulty in restarting or poor idling often occurs. This is also an important point when troubleshooting.
Hesitation is considered to be a light symptom of engine stall. But the symptom occurs only momentarily so a speedy, yet accurate inspection should be performed while the hesitation occurs. As for the cause of the hesitation, there are roughly two types, mechanical type in the engine, for example, the valve stick, and electrical type, for example, the operating EFI system. Further, another cause, such as an ECT shifting problem, can also be considered, so it is necessary to understand the malfunction from a wide point of view.

1. 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.
When there is conformity between the DTC and symptom
• If the symptom continuously occurs, the malfunction is judged to be in the area where the DTC is indicated.
• If the symptom does not occur, it is necessary to inspect while the malfunction is occurred by using the reproducing method.
When there is a hesitation malfunction, using diagnosis test mode, ascertain the malfunction area in which the malfunction momentarily occurs, and efficiently narrow down the malfunction cause.

2. Narrowing down using the data of ECU
By analyzing the data of ECU when the malfunction occurs, judge whether the sensor range/performance problem or the malfunction related to the actuator can be narrowed down or not.

3. Symptom occurrence condition confirmation
As for engine stall or hesitation, when there is difficulty in restarting or poor idling accordingly, or when the problem symptom occurs by using the reproduction method, etc. the occurrence conditions vary. Here, performing troubleshooting that matches in the symptom occurrence condition efficiently narrows down the malfunction cause.

(1) Difficulty in restarting after engine stalls
After the symptom occurs, proceed with the inspection following troubleshooting for difficulty in engine restarting.
(2) Restarts but idling trouble occurs after engine stalls
When the engine stalls as a result of poor idling, proceed with the inspection by following troubleshooting for poor idling.
(3) Symptoms occurs by reproduction method
When the malfunction occurs by using a reproduction method, the malfunction cause can be judged to be the area in which applied the reproduction method. Perform the troubleshooting narrowing down the malfunction at the area.
(4) Engine stall without idling trouble and difficulty in restarting the engine
The symptom occurs, however, when neither difficulty in restarting nor poor idling is accompanied by it, the symptom recurs only momentarily. Therefore, to observe the symptom is rather difficult. But when the symptom occurs, if the following items are inspected, the malfunction cause can be narrowed down to the fuel system or ignition system.

<1> Narrow down ignition system
It is difficult to clearly judge that the malfunction cause is in the ignition system. So narrow down the fuel system and after confirming that the system has no malfunction, inspect the parts and the connectors in the ignition system using reproduction method.

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