Engine Knocking Sound When Accelerating (Causes & Solutions)

Have you ever heard the metal clucking noise from your engine, during acceleration? It is a very common experience for many drivers, and they call it detonation, the engine knocking.

Things like a worn-out engine, failing knock sensor, lean air, fuel mixture, etc. are what cause the engine knocking sound when accelerating, so anyone can experience it.

In the course of this article, you will learn more about the thing that causes the vehicle to make knocking sounds while accelerating, types of knocks, how the engine combustion works, how to prevent or fix it, signs of clogged or dirty injectors, and every other thing that is related to the knocking noise of an engine.

What Causes Engine Knocking Sound When Accelerating?

When the mixture of air and fuel is not evenly burning, it can result in engine knocking. The knocking noise results from the uneven combustion of the air and fuel mixture.

The very common causes of an engine knocking are as follows:

  1. Overheating engine
  2. Lean air/Fuel mixture
  3. Clogged or dirty injectors
  4. Low level of octane gasoline
  5. Failing knock sensor
  6. Buildup of carbon
  7. Engine parts being worn out
  8. defective Spark plugs

1. Lean Air/Fuel mixture

Lean air/fuel mixture can cause detonation engine knock. It happens when an engine has excessive air or too little fuel.

When fuel is insufficient in the cylinders, that mixture will find it hard to move as fast as it should, resulting in numerous denotations called the engine knock.

Lean Air/Fuel mixture is caused in an engine when oxygen sensors, mass air flow sensors, fuel injectors, or fuel pumps are having issues.

2. Worn Out Bearings

When the rod knocks, it is the main sign of worn-out bearings. It happens because, the worn-out bearing, creates excessive clearances which makes the large end of your rods, come in forceful contact with the crankshaft at the top and bottom of your piston stroke.

Many times, when the bearing fails or begins to fail, you will notice a sign of a reduction in oil pressure.

2. Carbon Build-up

Carbon can build upon numerous elements in your vehicle’s engine, including such buildup in your combustion chamber, leading to engine knocking.

This is an easy fix because we have tools like the fuel injector cleaner, used to clean or break down the carbon deposits in an engine.

3. Faulty Knock Sensor

When one is working correctly, knock sensors become helpful and needed. They sense vibrations made by the knocking engine, then turn them into electrical voltage signs.

A failing knock sensor gives out untrue signs, that can lead to knocking as the engine may notice an untrue vibration, that is not present in the actual sense.

4. Defective Spark Plug / Bad Timing

Removing heat from a combustion chamber, your spark plugs move on a particular heat range.

Two things can lead to an engine knocking, too wide or narrow spark plugs. If one newly changed the spark plugs and starts hearing the knocking noise, there is a possibility that the new spark plug is incorrect and has to be replaced.

Spark plugs cause knocking in an engine when there is an incorrect gap between them.

5. Too Low Octane

High-octane fuel burns uniformly and efficiently and can resist knocks.

When the vehicle engine is rated and designed for high-octane fuel, you will encounter engine knocking whenever you use a low level octane fuel.

Therefore, when you change the vehicle’s fuel and notice the knocking, you can say that your vehicle malfunctions, when there is a low level of octane fuel.

Ensure you consult the owner’s manual to know the suitable octane rating for your car.

6. Engine Overheating

Engine overheating is among the prominent causes of engine knocking. A leak in an engine coolant mostly causes overheating, which extends to knocking noises and sounds before the engine knocks.

As an engine overheats, its aluminum material starts cracking, wrapping, expanding, and smelling. Then a wrapped cylinder can be separated from an engine block, which makes a leak on the gasket’s head, further causing a leak that will make the engine burn oil and coolant.

To prevent engine overheating, continue examining your engine temperature as frequently as possible.

Also Read: Whining Noise When Accelerating (Causes & Solutions)

Types of Knocks

We have essential engine knocks, which are further classified into other types. We will list five engine knocking types, that happen in a car:

  1. Detonation knock: very low octane
  2. Detonation knock: Fuel mixture/lean air
  3. Detonation knock: Faulty knock sensor
  4. Detonation knock: Bad timing
  5. Rod knock: Bearings that are worn out

How Does a Combustion Engine Work?

Engine Knocking Sound When Accelerating

The combustion process starts when fire from the spark plug, leads to a spark that ignites the fuel-air mixture in one’s cylinders. That flame quickly spreads to the entire mixture.

That heat from the burning air and fuel, makes the piston go up and down and drives your crankshaft. That crankshaft turns the reciprocating movement of your pistons into rotational movement and powers the entire vehicle’s system.

That burning fuel-air mixture creates so much pressure in the cylinder. The pressure pushes your piston downward, then turns your crankshaft, making your vehicle move backward or forward.

How Does an Engine Convert Heat Into Motion?

That heat from a burning fuel-air mixture, makes your pistons move down and up, driving your crankshaft. Finally, your crankshaft turns the reciprocating movement of pistons into a rotational movement that powers the entire vehicle’s system.

How Does Engine Knocking Sound?

When fuel/air detonates early, there can be a detonation/knocking sound. The reason is that pressure waves coming from immature combustion collide with one another, creating noise.

Deposits on the valves or pistons can also cause engine knocking. Likewise, when they ignite, it can result in knocking.

Find a mechanic to handle the confusing knocking sound, to avoid causing a road accident.

Engine Knocking Sound When Starting Your Car

If you notice a knocking or clunking sound as you turn on the vehicle, there is possibly an issue with the starter or transmission’s flex plate.

Sadly, that knocking noise as you turn on the car may be from either of these. It is an issue that has to be fixed immediately before it turns bigger and more expensive.

Changing one’s starter can be done in one day, costing about a hundred dollars. To change the flex plate, you’ll have to take out the entire transmission. It is a process in that you can spend from $1,000 and above.

Also Read: Gas Leaking From Bottom of Car (Causes & Solutions)

How to Fix Engine Knocking Sound When Accelerating?

Examine the fuel. It is the “least invasive” way of finding out engine knocking. Open the owner’s manual, and be sure of the octan that your car needs. If it needs 91 or more, and you’ve been stopping at 87, then a fuel octane may be the issue.

A second option is to change the filter and oil. If you can change the oil by yourself, it will not take longer than 30 minutes, or you can let your mechanic do the job within two hours or less. Any way you choose, it is not expensive to solve this problem.

As you confirm everything is alright with the oil and fuel, move to the spark plugs. You can swap the spark plugs by yourself if you are good with vehicles.

However, if it has gone past the 30,000-mile mark, change them. Also, if you just replaced the spark plugs and the knocking sound starts, you may have an unsuitable plug.

Most other things that cause engine knocking, not excluding rod knock sensors and worn bearings, are better handled by a professional mechanic because it requires taking out some engine components.

Below are detailed steps on how to fix an engine knock

How To Fix Engine Knocking

1. Scan the Engine Codes

When an engine knocking happens as your check engine light is on, you should use your professional code scanner. The OBDII scanner shows you the things that engine codes set, and helps in deciphering the thing that has led to the issue.

Readings can be gotten from the entire correct sensors, in real-time. Run the readings under different loads, to see the thing going on. It is best to cross-reference the readings with data gotten from the service manual, to know what is taken as normal.

When part of your code scanner appears faulty, you will have to change it. Many sensors are easy to change, but you should not try fixing something that you are not familiar with.

2. Perform Engine Maintenance

When knocking happens, exempting the check engine light, begin by carrying out the normal maintenance procedures for an engine. Change the oil and make sure to fill up the system properly. Then, from your owner’s manual, make use of the correct specified oil.

You can also use the engine cleaner, throttle body cleaner, or injector cleaner. The various cleaners can wipe from the passage’s, carbon buildup.

We also have cleaners that increase the fuel quality in your tank. Using the correct application helps in dissolving carbon buildup, and prevents additional blockage.

There is a possibility that one’s spark plugs have to be changed. This is because it can become contaminated or damaged with time. If you do not change your plugs when needed, the spark delay can result in knocking though it is simple to fix.

3. Increase in Fuel Octane Rating

When you are not using the correct octane rate for your vehicle, you should increase it to the premium suggestion. Check the owner’s manual for more information on the correct octane rate, for your vehicle.

When you increase the octane rating, ignition can happen at the correct level. In addition, you can temporarily use octane booster additives, to get it to the required rate.

4. Look Underneath the Vehicle

If you suspect the noise is from your driveline, you have to check underneath the vehicle and look at the driveshafts and CV joints. You can also look at your exhaust system, to ensure it is properly mounted.

5. Go to a Professional

When the problem is in such a way that you cannot explain, you are advised to take it to a professional to be guided properly. You can cause extra problems if you mess with what you do not know.

Most times, the mechanic charges an evaluation or diagnostic fee. Ask if there is a fee attached before the examination. The evaluation can show a problem, that one cannot fix personally.

Can An Oil Change Solve Engine Knocking?

We have different things that could cause engine knocking; an oil change can not solve it all. If your engine is knocking, you should take the vehicle to a professional mechanic, for the mechanic to detect the problem and suggest a solution.

If you want to change the oil, you must bear a few things in mind. First, make sure that you choose the correct oil for your vehicle.

This information can be found in the owner’s manual. Ensure to keep to the intervals that have been recommended for replacing oil. With time, old oil can wear down the engine components and give room for knocking.

If changing the oil does not solve the engine knocking issue, you should still ensure that the vehicle runs smoothly and well oiled. Call your local mechanic to get more information about engine knocking, and how to fix it.

Frequently Asked Questions – Engine Knocking Sound When Accelerating

What causes my car to make a knocking sound when I accelerate?

It is a normal experience for many drivers called detonation or engine knocking. Detonation occurs when fuel in your cylinder detonates before all other fuel.

At the time of ordinary operation, the spark plug begins its combustion process and burns fuel in your cylinder, hence regulating explosion. 

Why does my car make a knocking noise when I press the gas?

Detonation knock or engine knock is the sound heard when the fuel-air mixture in one’s cylinder is excessively detonating. Components of the fuel/air mixture can be ignited very early. As the mini fireballs collide, a knocking sound is made. 

Is it possible to drive a car with a knocking engine?

It is not suggested that you drive vehicles with a knocking engine. Detonation or engine knock is dangerous for the engine’s internal parts; it can lead to a repair price of above $3000 if one is not careful. 

What is the best way to stop the engine from knocking?

Detonation happens when the fuel-air mixture is not correct. To contradict this, one can add an octane booster inside that mix.

It helps ensure that the correct octane rating, which helps them stop knocking, is proper. The suggested minimum octane level in the United States is 87. 

If an engine knocks, how much does it cost to fix it?

For labor and parts, repairing the knocking engine will cost an estimated $2,000 to $3,000. When the damage becomes worse, you will spend on replacing additional parts. Do not turn off the repair because damages only become worse. 

What is the longest you can drive a car with an engine knocked?

As soon as the engine begins to knock, the rod fractures without a warning sign. It can happen as soon as you start in the driveway, or it can continue moving for 6 months. Subsequently, the engine blows, and you get stranded.

Final Words

There are times when, after serious troubleshooting, you will be unable to stop the knocking sound. When so, take the vehicle to a professional mechanic to look at it thoroughly.

Engine knocking is not always an engine’s death rattle. It does not take complex effort or time to repair, especially when you detect the problem on time.

Finally, listen to your vehicle. When a knocking happens, it’s unusual and not part of the car’s running condition. When you hear abnormal noise, ensure that you attend to it immediately.

Leave a Comment