How to Diagnose your Vehicle if The Engine Produce Abnormal Sounds? 2 of 2


Abnormal Sound and Noise Caused by Abnormal Combustion
3. After fire
Air fuel mixture is discharged without completely being combusted inside the combustion chamber. This unburned gas is retarded in the exhaust system and burnt comexplosively. bustion explosively. When the air fuel mixture is excessively rich, and the ignition timing slightly retards, this phenomenon may occur.
Main cause
• Air fuel mixture is excessively rich
There is an oxygen shortage and the air fuel mixture cannot be combusted completely.
The unburned gas is heated in the exhaust pipe, and “after fi re” occurs.
• Sudden deceleration and shifting down
Intake pipe vacuum pressure suddenly rises and the air fuel mixture becomes excessively rich.
Since charging efficiency also worsens, the two elements of “good compression” and “good air fuel mixture” are not satisfied. As a result, the combustion becomes unstable and “after fire” tends to occur.
• Ignition timing retards
Combustion duration becomes longer, the combustion process continues until the end of the explosion stroke and after burn occurs.
• Misfire
Sometimes misfire occurs due to a malfunction in the ignition system.
Unburned gas is heated in the exhaust pipe and after fi re occurs.
4. Back fire
This symptom occurs as a result of the air fuel mixture being taken in is combusted.
This is because the combustion process still continues even when combust commotion in the cylinder becomes slow and when the intake valve opens in the case of busted. Combustion Combus excessively
lean air fuel mixture or ignition timing retardation, etc. excessively “Back fire” tends to occur when starting while the engine is cold when accelerating during warm up.
Main cause
• Air fuel mixture is excessively lean
Combustion becomes slow and the combustion duration becomes longer. When the combustion process is not completed in the explosion stroke and continues to the next intake stroke, “backfire” occurs.
• Heat spot occurs
When heat spot occurs due to overheating, the air fuel mixture is ignited in the intake stroke. The air fuel mixture is combusted in the intake manifold and “backfire” occurs.
• Inappropriate valve timing and ignition timing
If these timings are inaccurate due to mis-operation, back fi re occurs and the engine does not run.

Related Post