Engine Knocking Sound: Causes And Effective Solutions

ByThe Old Racer
Table of contents

The knocking sound repeating at a high frequency from the car engine is the last thing drivers desire. It’s not only annoying but also a sign of your car engine suffering from some serious damage or problems. So, what are the causes of the engine knocking sound? How to identify and eliminate the knocking sound in your engine effectively? This post has the answers you are looking for!

What Is An Engine Knock?

Engine Knocking Sound Cause

The knocking sound in the engine occurs when the fuel/air mixture’s combustion in the cylinder is not ignited by the spark plugs. In simpler terms, the uneven burning of fuel in the engine cylinder will cause knocking. 

After a pocket burn, the engine will generate a little knock to ignite the pocket and continue the igniting process. This can only happen when the fuel or air mixture is burnt evenly and simultaneously rather than in small pockets. 

The uneven burn of fuel and air mixture will make the little shocks go off at different times and cause the annoying knocking sound. If you leave this issue going on, it may damage the engine’s cylinder and components. 

Engine Knocking Causes 

There are many types of engine knocking that lead to distinct issues, such as the detonation knock or rod knock. Identifying the problem is essential for fixing the engine and coming up with proper solutions. 

Here are the six main causes of engine knocking sound. 

Detonation Knock

In a properly functioning engine, the air and fuel mixture must be burned evenly in the cylinder’s single detonation. When this air/fuel mixture detonates in the cylinder more than one time, the detonation knock will occur. 

It causes a part of this mixture to ignite early and collide with the mini fireballs, thus generating that annoying knocking sound. Detonation knock commonly happens when the fuel level is too low compared to the octane rating. 

Bad Timing

There’s a computer that decides when your car engine puts the spark lugs on fire. However, a damaged or malfunctioning computer may make the spark plugs fire at the wrong time and create a knocking sound. 

Lean Fuel/Air Mixture

A lean mixture of fuel and air is caused by damage and issues in the oxygen sensors, fuel pump, airflow sensor, or fuel injectors. It occurs when your engine has too little fuel or too much air, which can lead to a lean fuel/air mixture. 

As a result, it will slow down the burning speed of the cylinder and lead to random, multiple detonations. 

Malfunctioning Knock Sensor

Since the firing timing and fuel injectors are controlled by a computer, a lean air mixture or detonation knock rarely occurs in a new car. A more common problem may come from your car’s knock sensor. 

This sensor is in charge of detecting a knocking engine and alerting the car’s control unit. A malfunctioning knock sensor may alert the knock even when the problem is not present. 

So, you should check the sensor before proceeding to examine your car engine. 

Worn Bearings

Another common cause of the engine knocking sound is worn bearings or rod knocking. The car wheel normally receives power from the crankshaft, which is turned on when the engine’s pistons move up and down. 

The rod bearings help smooth this movement, but they will make the pistons scratch against the engine’s crankshaft when wearing out. This rattling sound is very similar to a knock. 

Bad Pulleys/ Belt Tensioners

The knocking sound doesn’t always come from the engine but sometimes from the belt tensioners or pulleys. These accessory belts will turn when your car is running, and they have to be put under a proper tension level. 

If the tension is not right and causes the belt to bend or stress out, it will generate a rattling or slapping noise. Unfortunately, fixing these accessories is much simpler and more affordable than dealing with a knocking engine.

How To Fix Engine Knocking?

No one wants to hear engine knocking except the mechanic. 

Most of us will have difficulty determining if the noise is rod knock, valve lifter tap, rocker arm, or spark knock. However, here are some steps that you can do to fix engine knock before it causes serious damage.

First step: Change Oil and Filter

Oil lubricates all moving parts that helps dissipate heat and remove metal filings and other debris. Even if the oil filter removes many of the particles, sludge still builds up and can recirculate back into engine parts.

So you should replace the oil and filter every 5,000 – 8,000 miles. The best is 3,000 miles or every 3 or 6 months. 

Step 2: Using High Octane Fuel

Low-octane fuel may be cheaper, but repairing will be more costly and your engine performance is not running at full capacity 

So make sure your engine uses the manufacturer’s recommended fuel.

Step 3. Prevent carbon build up with fuel detergent

Carbon build-up can cause hotspots and premature fuel-air detonation and make a knocking sound 

Many fuels contain detergents to prevent carbon from building up on cylinder walls and spark plugs.

Step 4:  Cleaning the Combustion Chamber

The combustion chamber contains a lot of carbon deposits, which will reduce the volume and increase the compression, reducing the efficiency of the combustion process

You can hire a mechanic or handle it yourself according to the video below

Step 5: Handling Spark Plugs

An incorrect setup spark plug can cause detonation, generating a spark knock. It will not spark if the clearance is too wide or too narrow. 

Regularly checking and replacing spark plugs will help you avoid unnecessary damage

Step 6: Reduce charging temperature

Cool air will expand when heated, providing oxygen to the fuel-air combustion mixture. A lower air intake temperature and higher density engine intake charge help improve combustion and decrease the burn duration.

Step 7:  Increase Engine Speed

The engine can’t be heated up will cause carbon buildup. But you can take a run on the highway for an hour to clean out the pipes.

Step 8: Replace Knock Sensor

The knock sensor is also a common cause when it’s not properly positioned. However, this requires an experienced mechanic

Step 9: Make Mixture Richer or Leaner

The perfect mixture burns all the fuel in the chamber and leaves no oxygen. 

By lowering the compression temperature and reducing the incidence of premature detonation a rich mix will decrease knocking

At higher altitudes, the air will be thinner and need a larger volume to burn a similar amount of fuel in the air-fuel mixture. 

The burn in the combustion chamber is complete with a leaner mixture have less chance of detonation knocking

Quick summary

The first solution is to equip a higher octane rating on the engine’s gasoline, which can bear higher pressure. You should prioritize octane ratings that support carbon-cleaning additives. 

Then, upgrade and replace the worn-out wires or spark plugs in your engine. 

Don’t forget to change the engine oil to avoid low oil levels and improper lubrication in the engine’s components.

FAQs 

Is It Expensive To Fix An Engine Knock?

If you hire professionals to fix an engine knock, the labor and components cost can push the price up to $2000 or even $3000. If the damage is too severe, you have to pay even more to buy and replace new components for the engine. 

Therefore, never underestimate the consequence of the knocking engine. Take your care to the repair facility right after you hear the annoying knocking sound. 

How Long Can You Drive With A Knocking Engine?

When the engine starts knocking, its rod can fracture at any moment. If you are “lucky”, the engine may function for a few months before it breaks down. 

If you’re unlucky, the knocking engine can totally break down the next time you pull off the engine. Therefore, never drive a car with a knocking engine for long. 

Is Rod Knock Worth Fixing?

Rod knock is among the most serious issues, which indicates that your car engine is not working properly. This issue won’t be resolved, and it requires immediate reparation. 

Can An Oil Change Fix The Rod Knock?

No, an oil change cannot fix the fundamental issues of the rod knock. Even worse, oil changing may lower the engine’s pressure and make the problem more severe.

Final Thoughts

The engine knocking sound indicates that some components in your engine are malfunctioning, and the problem should be noticed. It will cost a lot of money and time to repair and replace the damaged components in the engine.

Ensure your vehicle is checked and maintained regularly, especially in its engine. I hope that the information provided in this post can help you avoid unnecessary loss and fix your knocking engine easier. Thank you for reading!

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