Knocking Sound Under Car When Accelerating Causes Fixes

Knocking sound under car when accelerating causes fixes will come up when you hear a strange knocking sound coming from underneath your car as you drive. This is one of the frequently asked questions.

Knocking Sound Under Car When Accelerating

It can be puzzling and even a little concerning, but don’t worry! In this post, you’ll explore some of the potential causes of the engine knocking sound when you accelerate and possible fixes.

Why Is Your Car Making a Knocking Sound When Accelerating?

Your car is making a knocking sound from beneath when accelerating because of worn shock absorbers or struts. Worn shock absorbers or struts cause a knocking sound when you accelerate. Shock absorbers and struts are part of the suspension system, which helps keep your ride smooth and comfortable.

They absorb the bumps and vibrations from the road, preventing them from getting to the body of the car. But over time, these components wear out due to regular use and exposure to harsh driving conditions. When worn, they can’t do their job properly, and that’s when you might hear a knocking sound when you hit the gas pedal. Also, they can cause a knocking sound under car when driving slow.

As you accelerate, your car’s weight shifts to the rear, putting pressure on the rear suspension. Worn shock absorbers or struts are not able to properly absorb this pressure, which causes the suspension components to hit each other or against the undercarriage of the car. This can result in a knocking sound that you hear from inside the car. It is the reason you are hearing the knocking sound under car when accelerating and braking.

  • Low-octane Fuel Can Turn Your Engine Into a Noisemaker

If you use low octane fuel in a car that is meant to use high-octane fuel, it can cause a knocking sound when you accelerate. Octane is a measure of how easily fuel ignites, with higher octane fuels being more resistant to premature combustion.

When you hit the gas pedal, your car’s engine ignites the fuel to create the combustion necessary to power the engine. However, if you’re using fuel with a lower octane rating than what your car’s engine requires, it may ignite too early before the spark plug ignites it. This early ignition can cause a knocking engine sound, which is like a little explosion happening too soon. If you are hearing the knocking noise when accelerating hard, this could be the reason.

This knocking sound can occur because the air/fuel mixture in the engine is not burning smoothly, leading to uneven pressure and vibrations. These vibrations can then create the knocking noise that you hear underneath your car when you accelerate.

  • Consequences of a Defective Knock Sensor: Sensor Gone Awry

A bad knock sensor is unable to accurately detect vibrations in the engine, leading to improper ignition timing. This can result in the fuel in the engine cylinder igniting too early or too late, causing a knocking sound when you accelerate.


The knock sensor in your car is responsible for detecting abnormal vibrations or knocking noises in the engine. When it detects these vibrations, it sends signals to the engine control unit (ECU) to adjust the ignition timing and prevent car knocking.

As you step on the gas pedal to accelerate, the engine produces more power, and the combustion process becomes more intense. If the knock sensor is not working properly, it may not detect the vibrations from the increased combustion, leading to incorrect ignition timing. This can cause the air-fuel mixture to ignite at the wrong time, resulting in the knocking sound you hear underneath your car.

  • Bad Spark Plugs Cause Your Car to Knock: Silent Saboteurs

Another possible reason you are hearing a knocking sound as you accelerate is because of faulty spark plugs. This component plays a crucial role in the combustion process as they create sparks that ignite the fuel and air mixture in the engine to propel the car. However, over time, spark plugs can wear out, affecting their performance.

Causes of Knocking Sound Under Car When Accelerating

Bad spark plugs or spark plugs with carbon deposits are unable to produce a strong spark or may misfire, causing incomplete combustion. This results in unburnt fuel being pushed into the exhaust system and can cause knocking sounds when you accelerate. Also, a misfire in one or more cylinders can trigger the check engine light.

The knocking sound arises from the abrupt and uneven burning of the fuel in the engine, which creates shockwaves that travel through the exhaust system and are heard as knocks underneath your car. This mixture can cause a single knock when accelerating.

  • Timing Mishaps: Engine Knock as a Sign of Timing Troubles

Bad timing is another possible culprit for the knocking sound you hear as you accelerate. Your car’s engine consists of various components, such as the camshaft and crankshaft, that work together to control the timing of the combustion process. The timing ensures that the fuel and air mixture is ignited at the right moment so the engine runs smoothly and efficiently.

However, if the timing is off, it causes problems such as knocking sounds. When the timing in your car is off, it causes the fuel and air mixture ignites too early or too late in the engine cylinder. As a result, there is uneven and uncontrolled combustion, which causes a knocking noise when you accelerate.

  • Low Oil Levels Can Leave Your Car Making Knocking Noise

One possible reason for this noise could be low oil levels in your engine. Oil plays a crucial role as a lubricant for moving parts and preventing them from grinding against each other. If the oil level is too low, engine parts can rub against each other, causing increased friction and heat.

This can lead to knocking sounds when you accelerate. The knock sound can be caused by rod knock as metal parts collide, creating rattling noise that travels through the car engine and is audible.

  • Rattling Rods: Worn Bearings Can Cause Your Car To Knock

Worn rod bearings could be the reason you are hearing noises coming from beneath your car as you accelerate. Rod bearings connect piston rods to the crankshaft in your engine. They help the piston rods move smoothly and avoid piston slap. Over time, due to wear and tear or lack of proper lubrication, rod bearings can wear out or be damaged.

When they are worn, they create a knocking sound as you accelerate. The knocking noise is caused by the excessive play or movement of the worn rod bearings, which can result in the piston rods hitting against the crankshaft or the engine block. This collision of metal parts creates vibrations that you can hear as a knocking sound underneath your car. It could explain the knocking sound when accelerating from stop.

  • Fuel Injector Woes: Malfunctioning Injectors Create Noise

Faulty fuel injectors could be the reason your car is making a ticking noise whenever you accelerate. Fuel injectors deliver the right amount of fuel into the combustion chamber of your engine. However, with time, fuel injectors can malfunction, which causes issues with fuel delivery.

Faulty fuel injectors are unable to spray fuel evenly or in the right amount, causing an imbalance in the combustion process. This can result in incomplete combustion or misfiring, which can create a knocking sound as the engine tries to compensate for the fuel delivery issue. As such, this could be causing the knocking sound when pressing gas pedal.

  • Worn Wheel Bearings: The Surprising Culprit Behind the Noise

If you notice a knocking sound from under your car when you accelerate, worn wheel bearing could be to blame. Wheel bearings allow your wheels to rotate smoothly on the axle. Over time, due to constant use and exposure to various road conditions, wheel bearings can wear out.

Worn Car Wheel Bearings

When wheel bearings wear out, they lose their ability to properly support the wheel, which can result in the wheel wobbling or vibrating as you accelerate. This can create a knocking or thumping sound that you may hear from under your car. The knocking noise is noticeable when you’re accelerating or taking turns.

  • Transmission Issues Cause Knocking Noises When Accelerating

The transmission in your car is responsible for controlling the power generated by the engine and transferring it to the wheels. However, transmission issues such as worn mounts can cause a knocking sound under the car when you accelerate.

Transmission mounts hold the transmission in place, but over time they can wear out, causing the transmission to move during acceleration. This movement can result in a knocking noise as the transmission shifts or moves around.

Another cause is low transmission fluid since it causes the transmission to make knocking sounds when you accelerate, as the internal components are not properly lubricated, creating friction and noise. Also, a faulty torque converter can cause a knocking sound as it struggles to properly transfer power during acceleration. All these can cause transmission knocking when accelerating.

What Is the Best Fix for Knocking Sound When Accelerating?

The best fix for the knocking noise coming beneath your vehicle when accelerating is to visit a professional mechanic. Seeking help from a professional mechanic is a reliable solution. These experts have the necessary auto repair knowledge, experience, and tools to diagnose the underlying issue accurately and provide effective fixes.

A professional mechanic will carefully inspect your vehicle, including its engine, suspension, fuel system, and other components that can cause the knocking sound. This will help determine the best course of action. The solution may involve repairing or replacing faulty parts such as shock absorbers, struts, knock sensors, spark plugs, timing components, fuel injectors, or wheel bearings, depending on the root cause of the issue.

In addition, professional mechanics have access to manufacturer-recommended repair procedures and genuine replacement parts, ensuring that the fixes are done correctly and with quality components. Also, you get valuable advice on preventive maintenance measures to avoid a similar issue in the future.

  • Use the Right Fuel: Eliminate the Engine Knocking Noise

Using the right fuel with the appropriate octane level can be a simple yet effective solution. To resolve the issue of the engine knocking sound when accelerating, start by making sure you use fuel with the octane rating recommended in your car’s owner’s manual or by the manufacturer.

By using the correct fuel, you promote smoother combustion in your engine reducing the occurrence of knocking sounds. Higher octane fuel can help prevent knocking, especially in high-performance or turbocharged engines that are more prone to this issue.

  • Engine Maintenance Role in Eliminating Car Knocking

A knocking sound under your car when accelerating could be a sign that your engine needs some TLC. Engine maintenance is crucial in keeping your car running smoothly and quietly. Regular maintenance tasks like oil change, replacing worn spark plugs, and keeping the timing belt in good condition go a long way in resolving engine-knocking issues.

Fixes of Knocking Sound of Accelerated Car

By taking your car for regular tune-ups and inspections by a qualified mechanic, you can identify and address any potential issues before they worsen. Proper engine maintenance can help prevent worn rod bearings, faulty fuel injectors, and other engine problems that may contribute to knocking sounds when accelerating.

  • Scan for Error Codes to Silence Your Car’s Knocking Sound

Using a scanner to check for error codes is another solution you can try yourself. When your car’s engine experiences a problem, it often triggers a diagnostic trouble code (DTC) that gets stored in its computer system. Codes such as this one can provide valuable information about the issue that’s causing the knocking sound.

By using an OBD-II scanner, you can connect to your car’s computer and read these codes to get a better understanding of what’s going on. Once you retrieve the error codes, you can look them up in a code library or consult a professional mechanic to interpret what they mean.

This method is best if you are looking to get the knocking sound fixed economically and quickly, as it allows you to pinpoint the issue more accurately instead of randomly replacing parts or guessing at the problem. Although scanning for error codes can be helpful in diagnosing the cause of the knocking sound, it’s not always a foolproof method.

Some issues may not trigger a DTC, or the codes may not provide a clear-cut answer. It’s, therefore, best to consult a qualified mechanic who can diagnose the problem.

Knocking Sound Under Car When Accelerating Details

Why Does My Car Make a Knocking Sound Under Acceleration?

If your car makes a knocking sound under acceleration, it can be worrisome. However, there are thumping noise solutions when driving that can help. This issue could indicate a problem with the engine, fuel system, or exhaust system. It’s best to have a mechanic inspect and diagnose the cause of the knocking sound to prevent further damage and ensure your safety on the road.


If you are hearing a knocking sound when accelerating, it’s important to understand the potential causes and possible solutions.

Here is a quick summary:

  • Possible causes include worn shock absorbers, bad spark plugs, low engine oil, and faulty fuel injectors.
  • Solutions include taking proactive steps such as regular engine maintenance, using the right fuel, and scanning for error codes.
  • You should seek professional help for an effective fix.

With this understanding, you can now take care of your car and promptly address issues that may cause a knocking noise as you accelerate.

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