Automotive Troubleshooting Insufficient Power


The causes of insufficient power are roughly classified as follows.

• Poor acceleration
The vehicle can run smoothly, but acceleration as a reaction of the throttle valve opening is not done.
The power does not react to the throttle valve opening change.

• Insufficient power
When driving uphill, speed cannot be gained. The power when the throttle valve is fully opened is insufficient. When troubleshooting for insufficient power, it is necessary to pay attention to the following.
(1) Understand what the customer points out and what he wants you to do.
(2) To perform an accurate troubleshooting, fully perform diagnostic questioning. If the vehicle still has diagnosis codes, it is important to check the freeze frame data and create the similar conditions and surroundings to those when the symptom occurs so as to reproduce the symptom.
(3) It is difficult to make a judgement based on the value from the tester, etc., so perform a road test paying attention to the following factors.

• Drive another vehicle of the same model and compare it with the one in which the symptom occurs.

• Actively involve two or three other people in the road test and make a judgement based on several opinions.

• Perform a road test with the customer whenever possible.
As for troubleshooting for insufficient power, it is important to judge the entire vehicle, not only the engine but also the drive train system, brake system, etc. and perform the appropriate procedures.
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, confirm the relationship between the DTC and the problem symptom.
2. Vehicle condition inspection
(1) Basic inspection
When the symptom confirmation is difficult unless driving, for example, insufficient power, to proceed the work efficiently, perform the basic inspection before the road test. The malfunction cause may be found in this basic inspection. A basic inspection is performed before verifying the symptom that the customer points out. Inspect the condition of the vehicle, take notes, and then perform a road test without altering the state of the vehicle.
(2) Symptom confirmation by road test

• Drive the vehicle together with the customer and perform the road test.

• If the test cannot be performed with the customer, perform road test according to the information obtained from the diagnostic questioning and the symptom occurrence condition based on the freeze frame data.

• Confirm the system and judge whether it is malfunction or not, there is conformity between DTC and/or vehicle inspection result and malfunction. If every DTC functions are used during the road test, it will be easier to find the malfunction cause.

• When performing a road test in check mode, the possibility of DTC detection will be higher.

• Use equipment to store the ECU data, perform the road test, and analyze the ECU data when the malfunction occurs. These procedures can detect an abnormality that the DTC does not output, such as a sensor range/performance problem or a malfunction in the actuator.

3. Narrowing down using data of ECU
By analyzing the data of ECU when the malfunction occurs, judge whether the sensor range/performance problem that cannot be detected by the DTC and malfunctions in the actuators, can be narrowed down or not.
Inspection methods

4. Troubleshooting method determined according to road test

• Some symptoms of insufficient power appear characteristically depending on the malfunction cause. Therefore, it is important to perform the road test while keeping the malfunction cause and the characteristics of its appearance in mind.

• A diesel engine vehicle does not exhaust white smoke while warmed up. If white smoke is observed, it can be judged to be a malfunction. However, immediately after the engine starts in extremely low temperatures, it may appear the white smoke, but in fact this is actually vapour, so it is important to observe carefully. Perform diesel smoke density inspection at no-load sudden acceleration beforehand to narrow down the malfunction cause by combining the inspection result with the symptom occurrence condition at load test.
Verify the symptom occurrence conditions without having any preconceptions and judge where the malfunction cause exists. In some cases, the malfunction cause is not only in the engine control system but also in the mechanical portion or drive train system relevant area, etc.

5. When there is a white smoke in diesel engine
Narrow down the malfunction cause depending on the conditions in which the white smoke occurs.

• White smoke is exhausted from almost all engine speed ranges
As for this cause, a malfunction in the fuel and the compression system is considered.

• Water is mixed into the fuel.
• Fuel cetane rating is low.
• Compression pressure is low.
• White smoke is exhausted when the engine speed is in the middle to high range
As for this cause, a malfunction in the injection pump itself, intake and fuel systems are considered.

• Clogging of fuel filter

• Dirt of air cleaner element

• Injection pump internal failure

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