Engine Knocking When Accelerating (Causes and How to Fix It) - My Car Makes Noise (2024)

If you’ve ever put low-octane fuel in your high-octane vehicle, you might’ve heard some weird sounds. That “engine knocking” is what happens when the fuel in your tank ignites at the wrong time.

Putting the wrong fuel in your car is one major cause of engine knocking, but other causes include faulty spark plugs, worn bearings, or a bad knock sensor.

Engine Knocking When Accelerating (Causes and How to Fix It) - My Car Makes Noise (1)

Contents

What Is Knocking Noise When Accelerating?

A knocking noise when you’re accelerating is a tapping or pinging sound that gets louder and faster as you speed up. It may or may not be present at idle, but it will likely be most noticeable when you’re putting your engine under a heavy load.

What Does Engine Knocking Sound Like?

An engine knock has a telltale pinging or tapping sound. Some have compared it to the sound of metal balls clinking together, while others have likened it to a soft, quick knock on a door or a pencil tapping on a desk.

That said, specific engine problems will cause knocking to come and go or increase at certain times. The sound combined with when you hear it will be a good indicator of what the problem might be.

For example, a rod knock, which indicates a problem with your rod bearings, will increase as you accelerate or if your engine is under heavy load.

When your car is idle, a knocking noise that eventually goes away could indicate an issue with your exhaust gaskets.

Another cause of knocking at idle is improper fuel in your tank. You’ll also hear this type of knocking while accelerating, too.

What Causes Engine Knock When Accelerating?

There are several different causes of engine knocking. Most are called detonation knocks and happen when your gas detonates at the wrong time or incorrectly. There are a few other causes that you should be aware of, though.

Low Octane Fuel

The first and most common cause of engine knocking is a detonation knock caused by low-octane fuel. High-octane fuel, also known as premium or high-test, remains more stable at higher temperatures than low-octane fuel. Therefore, if an engine is designed to hold premium fuel, that means it’s designed to combust fuel at a higher temperature.

If a vehicle is rated for premium and you fill it up with regular, you’ll likely hear some knocks and pings when the gas ignites at the wrong time during the combustion process. Regular fuel can’t always withstand high engine temperatures the same way premium fuel can, so it can ignite and cause knocking.

Rod Knock

Worn bearings in your engine are another common cause of engine knocking. Your engine’s bearings are what keep the pistons moving correctly, opening and closing the intake valve smoothly.

Once those bearings start to wear out, they’ll cause your rods to tap against your crankshaft. That tapping is called rod knock, indicating that the bearings may need to be replaced. Unfortunately, they’re not exactly easy to get to, so you could be looking at a hefty repair bill.

Bad Knock Sensor

Your vehicle is full of sensors that are constantly checking to make sure each component is working as it should. When a sensor goes bad, your check engine might flip on. In the case of a bad knock sensor, a telltale symptom is a knocking sound coming from your engine.

The knock sensor is responsible for monitoring the noises your engine makes. It essentially regulates how and when the fuel in your engine combusts. If the knock sensor malfunctions, it could cause your fuel to detonate at the wrong time.

Spark Plugs

Spark plugs are what cause the fuel in your engine to ignite. Similar to using low octane fuel, if your spark plugs are faulty, there could be issues with gas combustion that could lead to knocking. Faulty spark plugs could also cause a dip in engine performance, so it’s important to get them replaced promptly.

The main reason a spark plug could cause knocking is because it’s degraded and simply needs to be replaced. Most manufacturers recommend replacing your spark plugs every 30,000 miles, but how long your spark plugs last will depend on their quality.

Improper Fuel/Air Mixture

When you start your car, a mixture of gas and air enters your engine. For your engine to work perfectly, that air and fuel mixture must be precise. When the fuel-to-air ratio is off, the mixture becomes “lean.” In other words, too much air and not enough fuel make your engine unhappy.

The main components you’d want to check out are your oxygen and mass air flow sensors, your fuel pump, and your fuel injectors. If any of those fail, your engine won’t work as intended.

Engine Knocking When Accelerating (Causes and How to Fix It) - My Car Makes Noise (2)

How to Fix Engine Knocking When Accelerating?

First, check your fuel. This is the “least invasive” method of diagnosing engine knocking. Pop open your owner’s manual and double-check what octane you should put in your car. If it calls for 91 or above and you’ve been loading up with 87, fuel octane is likely your problem.

Another option is to change your oil and filter. If you know how to do an oil change yourself, it won’t take more than a half-hour out of your day. Or, you can take it to a mechanic and have it done in an hour or two. Either way, it’s another inexpensive option that could solve your problem.

Once you’ve confirmed everything is good with your fuel and oil, you can move on to yourspark plugs. If you’re handy with cars, you can probably swap your spark plugs out yourself. If they’re past their 30,000-mile mark, replacing them could do the trick. Likewise, if you just got your spark plugs replaced and you’re hearing knocking, you might have a faulty plug.

Most of the other causes of engine knocking, including worn bearings and rod knock sensors, are best left up to a trained mechanic because they require the removal of certain engine components.

Is It Safe to Drive With a Knocking Engine?

In some cases, it’s safe to drive with your engine knocking, although you should still address the issue as soon as possible.

If the issue is the wrong fuel, you won’t have any trouble getting to the gas station to fuel up properly or running the tank to empty. Likewise, getting your spark plugs changed is a relatively quick process. You won’t harm your vehicle if you drive it to the mechanic.

However, continuing to drive when your bearings are bad could lead to major engine problems if you don’t address them. The bearings are deep inside your engine and, if left unchecked, could lead to issues with your pistons and other components. Engine rebuilds aren’t cheap, and if you wait for the problem to correct itself, it’ll ultimately do more damage.

What to Do if the Engine Knocking Sound at Acceleration Persists

Sometimes, even after excessive troubleshooting, you might not be able to get rid of that knocking sound. If that’s the case, you should take it to a mechanic to get it looked over more thoroughly.

Engine knocking isn’t always the death-rattle of an engine. In fact, in most cases, it won’t take much time or effort to fix, especially if you get it diagnosed early. Most importantly, you should listen to what your car is telling you. Knocking in your engine isn’t part of your vehicle’s normal running condition. So when you hear that rattling ping, be sure to address it right away.

Engine Knocking When Accelerating (Causes and How to Fix It) - My Car Makes Noise (2024)

FAQs

Engine Knocking When Accelerating (Causes and How to Fix It) - My Car Makes Noise? ›

Low Engine Oil

How to fix engine knocking when accelerating? ›

How to Fix Engine Knocking?
  1. The first step in trying to fix engine knocking is to upgrade to gasoline with a higher octane rating. ...
  2. Give your engine a tune-up that includes new spark plugs and wires.
  3. Regularly change the oil in your vehicle and monitor for a low oil level.

How do you get rid of engine knocking noise? ›

In the cases where low-quality fuel is to blame, changing to a higher-octane fuel can possibly help alleviate the issue. Another effective method is to clean carbon buildup from the combustion chamber using dedicated fuel additives or cleaners, which can help reduce knocking sounds.

Can a car with a knocked engine be repaired? ›

A mechanic can diagnose the problem and let you know what needs to be done to fix it. Engine knocking can be caused by several factors, including a build-up of carbon deposits, low oil levels, or a piston problem. While some of these causes can be fixed quickly, others may require more extensive repairs.

Can adding oil fix engine knock? ›

No, adding oil is not a solution to stop engine knock. Engine knock (pinging or pinking) is typically caused by premature fuel ignition, which can be due to low-octane fuel, engine design, or carbon buildup. Adding oil may not address the root cause and may even worsen the issue.

Can a knocking engine be saved? ›

If you're fortunate, refilling the engine with fresh oil may cause the noise to subside (at least temporarily). The bad news is, even if the noise does go away, there's a good chance internal engine components have already suffered permanent damage due to lack of lubrication.

What can be mistaken for rod knock? ›

Failing Belt Tensioners or Pulleys

Failing belt tensioners and pulleys won't actually cause rod knock, but they can create rattling noises that imitate rod knock. If your serpentine belt tensioner or pulley goes bad, having them replaced is a simple task that can be completed for a low cost.

How do I temporarily stop my engine from knocking? ›

How to Stop a Car from Knocking
  1. Checking Engine Temperature.
  2. Increasing the Octane Level in your Fuel.
  3. Cleaning Your Combustion Chamber.
  4. Inspecting/Replacing your Spark Plugs and/or Wires.
  5. Checking Your Car's Timing.

Is it safe to drive with a knocking engine? ›

Knocking can be a sign of a serious problem with your engine, so you should avoid driving and book a diagnostic test as soon as possible. Using your car when it is making a knocking sound can be dangerous, and you may end up with a more expensive repair bill.

How to quiet a noisy engine? ›

How Can You Quiet Your Car Engine? Once you verify the lifter ticking is not caused by a worn-out lifter or some other damaged part, the best thing to do is change the oil. Get rid of all the oil currently in the engine and flush it out before adding new oil.

Can seafoam fix engine knock? ›

Lifter noise is caused by sticky varnish that develops from old oil residue that build up in the crankcase over time. Sea Foam (or High Mileage for older engines) added to oil will work to reliquefy and clean away the varnish that's causing the noise.

Do I need a new engine if it's knocking? ›

If you've got a rod knock, stop driving the vehicle - your engine is on limited time and will need replacement or major repair.

Can a clogged oil filter cause knocking? ›

Changes in your engine's typical sound could also indicate reduced lubrication due to a clogged oil filter. While not always caused by a contaminated oil filter, any ticking, knocking, or unusual engine noises warrant getting your vehicle checked by a mechanic.

Why does my engine knock when I accelerate? ›

Engine knock often occurs when the air and fuel mixture in the engine cylinders is not properly ignited in a controlled manner, or when metal components are hitting together that shouldn't be. When an engine functions properly, fuel (usually gasoline) is mixed with air and then compressed.

How to fix engine knocking sound? ›

This condition is also called a spark knock. The Fix: You'll need to change your spark plugs by pulling the wire plug from the engine. Then, fit a socket wrench with an extension bar to slowly remove the spark plug from its housing. Swap the old spark plugs with the correct replacement plugs using the ratchet.

Can engine knock destroy an engine? ›

This can cause severe engine damage. The reason why you are hearing knocking is that the pistons are knocking against the crankshaft walls. If left unrepaired, you will damage the crankshaft and render your engine inoperable.

Why does my engine knock when I hit the gas? ›

Knocking occurs when fuel burns unevenly in your engine. When everything is going as it should, and the cylinders have the correct mix of air and fuel, the mixture burns in a controlled, progressive manner. After each cylinder's air/fuel mixture burns, it should create a small “shock wave” in your engine.

How to cure engine pinging when accelerating? ›

If it's a fuel-grade problem, sometimes you just need to increase the octane that you buy at the pump. Bottom line: If your engine is pinging, and if the fuel upgrade hasn't helped, you will probably want to bring it to a certified mechanic.

Does knocking damage an engine? ›

Severe knocking can lead to catastrophic failure in the form of physical holes melted and pushed through the piston or cylinder head (i.e. rupture of the combustion chamber), either of which depressurizes the affected cylinder and introduces large metal fragments, fuel, and combustion products into the oil system.

Why is my engine knocking and shaking when accelerating? ›

Shaking while accelerating could be caused by misfires, crankshaft damage, transmission failure, CV joint damage, or a cracked engine mount. Do not continue driving if your vehicle shakes when you accelerate. You may cause serious damage to your engine or lose control of the vehicle at any moment.

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