What Causes Engine Knocking Sound?

Knocking occurs when fuel burns unevenly in your engine’s cylinders. When cylinders have the correct balance of air and fuel, fuel will burn in small, regulated pockets instead of all at once.  After each pocket burns, it creates a little shock, igniting the next pocket and continuing the cycle. When your car’s ignition system sends a spark to each cylinder at the same time, a small knock is heard. This knocking results in a rough idle and injector pulse modulation, which slowly wears out your fuel injectors. 

The knock is powered by the ignition system and audible at any engine speed. If the engine knocks or makes a knocking sound, but does not cause any operational problems, it is not necessarily bad; the engine is just old and the sound is a mere artifact of age. Why does it knock? Over time, the ignition wires that fire the spark plugs lose energy. These “weak” knock wires can be replaced to eliminate the knocking. When replacing knock sense wires, you can increase the engine’s horsepower when doing so. When replacing the ignition wires, your car’s fuel efficiency will suffer, and you could damage the engine.

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Reason for Engine Knocking

In nearly all cases, knocking is caused by an uneven burn of fuel in the combustion chamber. This means that the spark plug fires at a slightly different time than neighboring plugs, creating a unique knock. The engine’s compression ratio and tune can also cause knocking. These factors are far too complicated to describe here, but I can assure you that they exist. If your car is knocking, it means the combustion chamber is not burning the fuel and air mixture evenly. These two factors can be easily tested using the following steps.

  • Test 1: Ignition system check

Turn your car’s engine on and allow it to warm up, then step on the gas. If you hear an uneven knock, wipe out the plug and repeat until no knock is heard. This is your “weak knock” or “detonation” problem. If this is the case, your engine will need to be replaced due to the risks of the knock causing a complete explosion.

  • Test 2: Spark plugs

Using a multimeter, check your car’s existing spark plugs to see if they are evenly worn. If the gap is off, replace the spark plug and continue test 2. This test requires some mechanic knowledge, so if your car is still within warranty write your garage an angry letter. If you’re trying this on your own, I hope you’ve got extra insurance.

  • Test 3: Spark plugs

When replacing the spark plug wires, replace the first two with two-conductor new ones. This prevents a possible misfire when the current from the other two wires tries to reverse directions. If your misfire is minimal and you don’t notice too much of an increase in knocking, replace all four wires. There is no reason not to.

  • Test 4: Spark plug gap

Using a spark plug gap tool, check the gap of each spark plug. If the gap is off, turn the wrench slightly and use a new thin coat of dielectric grease to try to get the gap back to where it should be. If this still doesn’t fix the problem, replace the spark plug.

Once you’ve finished testing and repaired your defective ignition system, check to see if the knocking has stopped. If it has, then continues with the next step. If not, it is best to get your vehicle serviced at a reliable services and repair centre.

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