Home Diagnosis and TroubleshootingEngine Problems Engine Knocking – Knock Knock, Who Is There?

Engine Knocking – Knock Knock, Who Is There?

by Jordan Harris
Engine Knocking

Are you noticing some weird sounds coming from the engine? Maybe it’s something like an engine knocking sound? This sounds serious, to be honest. Engine knocking is something that isn’t good for you and your car. But what could be the cause for this sound? There can be many reasons why your engine is knocking. We are going to cover all of them for you to have a better idea of what could cause this issue.

Learning to troubleshoot problems and noticing strange symptoms on your car is going to give you that extra edge, and you are going to avoid some incompetent mechanics misdiagnosing your car. Knowing a lot about the mechanicals and how you can troubleshoot is going to save you a ton of money in the long run.

This is especially if you have a problem like this one with the engine knocking. As we said, the knock can be caused by numerous components, and you have to train your ears to recognize where the knock is coming from, and how to diagnose the issue as soon as possible. That’s why we are going to explain all of the ins and outs of diagnosing this issue.

In this article, we are going to learn what is the engine knocking, and what are the probable reasons why your engine is knocking. Having learned the reasons, it’s then time to learn how you can diagnose the issue with your car that is causing the knocking. And lastly, we’ll look at the cost to fix this problem with the engine knocking. So, let’s discuss.

What Is Engine Knocking?

Engine knocking is an audible sign that there is something wrong inside of the engine or in the combustion process. This engine knocking can get really expensive if you decide to ignore it and pretend like it’s nothing.

In most cases, knocking can appear because of the bad timing of the engine. Bad timing means that the components in the engine do not work properly, and are not at the right timing.

This bad timing means that the ignition does not happen when it should. When the ignition is wrong, many issues can start to appear including the engine knocking.

Engine knocking can also be caused by mechanical problems within the engine as well. That’s why you need to train your ear on how to recognize the symptoms. Different knock emits different sounds. You need to recognize the sound to know what is causing this issue to appear.

Plus, we are going to include some videos to show you the different engine knocking sounds and what do they mean. This would be useful for you to compare the sounds with your engine, and see if some of these sounds match the sound that your engine makes.

Diagnosing an engine by yourself is going to give you a lot of knowledge on the mechanical problems that can happen in your car. Solving the mechanical issues in your car is going to save you thousands of dollars during the ownership of your car. It’ll be more worth it to spend this money elsewhere, on upgrades or servicing.

But why this knocking happens in the first place? What is the reason why the engine starts knocking? Well, let’s find out why.

Why Is My Engine Knocking?

There are two reasons why your engine is knocking. One of the reasons is a detonation knock and this knock is related to the ignition of the fuel inside of the cylinder.

When there is bad detonation in the cylinder, the cylinder will develop a knock. If the fuel ignites too early, then it is a timing-related issue, and this can cause knocks to develop. This happens because the fuel is not burning evenly and a bunch of fireballs is colliding into the cylinder, so this causes the knocking noise.

Engine Knocking

Another reason why you can have a knocking noise is that some mechanical components have gone bad. The most notable sample for this problem is the rod knock that we are going to elaborate on later in the article in great detail. Other reasons can be bad belts and tensioners, bent valves. We also going to cover them as well.

The important thing to note is that when you hear your engine knocking, don’t panic. Panicking will make things worse and you probably going to do a bad job of diagnosing this issue.

Nobody likes engine knocking, but there is nothing that you can do to stop it. That’s unless you diagnose the issue properly, and see what is the real culprit. In the next chapter, we are going to cover all of these culprits that can cause engine knocking to develop.

Detonation-Related Engine Knocking

As we said, there is detonation-related engine knocking and there is also mechanically related engine knocking. You need to differentiate these two things to get to the real culprit. In this chapter, we will go through all of the detonation-related reasons why the engine is knocking. So, let’s get into it.

Low Octane Rating

A low octane rating can cause bad detonation and engine knocking. This is the case with most cars that require premium fuel. If you add some fuel that is below the octane rating, the engine will not work properly and start knocking. This type of knocking is the most common type of knock found in engines.

But what is an octane rating? Octane rating is basically the ability of the fuel to withstand compression. The higher the octane rating, the more ability of the fuel to work on a bigger compression engine. This allows the fuel to deliver considerably more power compared to lower octane rating fuels.

Adding high octane gas to a car that has average compression will not do much. Basically, the engine will continue working as it did before. But if you add low octane gas into a car that has a high compression engine, it’s going to cause engine knock.

That’s why you should always stick to the recommended fuel for your vehicle. That’s since the engineers from the factory are cleverer than us, and they know what fuel fits our cars the best. They have done countless hours and miles of testing to find the right formula.

Lean Air To Fuel Mixture

Lean air to fuel mixture can also cause your engine to misfire and start knocking. These misfires will resemble small knocks that will annoy you while you are driving on the road.

The lean air to fuel mixture means that there is too much air in the combustion chamber. The more air you have in there, the more misfires are going to happen and the engine would run pretty badly.

The average air to fuel mixture should be 14.7 to 1. That means a ratio of 14.7 air to 1 fuel. If the level of air goes above the 14.7 ratio, your engine will start to misfire and start to knock.

This problem can be caused by multiple reasons. But the most common ones are the bad sensors. More specifically the mass airflow sensor and the O2 sensor. Also, this problem can be caused by vacuum leaks in the vacuum lines and the intake manifold. In addition to this, are the PCV valve and the EVAP solenoid. These components open and close. When they fail, there is too much gas in the combustion chamber. This causes troubles for the engine and it’s hard for the engine to run properly.

Lean air to fuel mixture can be tricky to diagnose. So, you should know from where to start. The first step is by getting an OBD2 scanner and scanning the car for codes. These codes are going to tell you a lot about your car and what components are going bad.

For example, if you get a code about the mass airflow sensor, it is a good idea to inspect the sensor and see if it’s good or not. Give it a good clean. Then, you can check other components like the vacuum lines, injectors, fuel filter, and O2 sensor.

Bad Timing

Bad timing can also be one of the culprits that can cause engine knocking to appear on your engine. The bad timing means that the ignition timing is wrong.

For the combustion process to be perfect, the timing needs to be perfect as well. The spark needs to produce a spark at the right moment. A fraction of a second late or early can cause the engine to misfire. In turn, this produces a knocking sound.

These misfires can lead to other problems as well. They will for sure damage your spark plugs. Then, these damaged spark plugs will make the engine run even worse.

The next symptoms will be carbon deposits to build up on the valves and the valves will not seal properly. This not sealing is going to cause loss of compression and other very bad symptoms that will happen to your engine.

You need to address the timing issue because if you leave the engine knocking, much worse things are going to start to develop. These are things that potentially will scrap your engine or lead to many very expensive repairs. You don’t want to pay a lot of money on repairs that are fairly inexpensive to do.

Take your car to a workshop and let them adjust the timing for you. This is since adjusting the timing is not such a simple thing to perform, especially for beginners. You will pay a few hundred dollars to get this service and your engine is going to thank you later.

Bad Knock Sensor

A bad knock sensor can also cause your engine to knock. This is the case because the knock sensor is designed to recognize a knocking issue on your engine. And if this sensor has failed, it’s going to allow the engine to knock and will not alert you.

Modern cars have a ton of electronics on them. Everything needs to be perfect for the car to work properly. The air to fuel mixture, the injectors, timing, etc. That’s why these sensors were designed with finding knocking problems and tell the computer to adjust the air to fuel mixture by itself without you needing to adjust the timing by yourself.

But these sensors can fail. When it does, knocking can develop since the computer doesn’t know if there is a knock and that it needs to readjust itself.

This will result in annoying engine knocking for you. But you can address this problem by scanning the car with an OBD2 scanner tool and find what causes the engine knocking. If the knock sensor is bad, then you will have to replace this sensor with a new one. After replacing the sensor, the car should readjust the timing and air to fuel mixture by itself and the problem would be solved.

After this, you can clear off the codes if there are any and wait if something would pop up again. If there are no more codes, then you are good to go. The engine should work perfectly and you shouldn’t worry anymore about your engine knocking issue.

Mechanical Problems

As we mentioned, there are detonation knock-related issues and there are also mechanical knocking-related issues. The mechanical-related issues are much worse than the ignition ones. This is the case because when it comes to detonation knocking, a simple timing readjustment or replacing a sensor or two would do the trick. But if your engine has a mechanical knocking, then this is bad news, because solving these problems can sometimes cost thousands of dollars.

Engine Knocking

Unadjusted Valves

Unadjusted valves can cause the engine to knock as well. This knock can be pretty annoying. When the valves are unadjusted the sound usually comes from the heads of the engine.

If you remove the heads, you will notice how to rockers are loose and have a lot of play on them. To adjust the valves, you need to get the right tool for the job.

There are special tools that are made for adjusting valves. You will also need a tool that will measure the space between the rocker and the valve. This tool is called a feeler gauge. You need to have a feeler gauge in order not to adjust them too tight. Adjusting them too tightly will result in poor engine operations, or it won’t work at all. That’s since the valves will remain closed or open all the time.

For this job, visiting a shop that has experience in this type of work is a good idea as well. They will tackle this work in no time and will perform a small tune-up for you. After this work, your engine will run perfectly as it came from the assembly line.

Lifter Tap

Lifters can also cause some tapping or engine knocking noise. This sound that the lifters are making is pretty subtle and can be described as a tick.

It is normal for some engines to start ticking after 100,000 miles. Especially HEMI engines that are notorious for this problem.

But this problem is not that serious and can be easily solved by replacing the lifters with new ones. Also, a small valve job with new valve stems and valves is going to help a lot in terms of performance and returning the engine to factory specification.

This job is probably going to cost you between $500 and $1000. It’ll depend on where you take your car to, and how extensive the repair is going to be. More parts replaced equals more money spent on labor and parts.

Carbon Buildup

Some engines are notorious for developing carbon deposits. This is most prevalent on diesel engines and direct injection gasoline engines. There isn’t a direct-injection gasoline engine that does not have this problem.

This can be attributed to the design of these engines, and those high-pressure fuel pumps and injectors that they are using. All these components are creating a lot of carbon deposits in the intake and exhaust ports of the engine head.

This problem can cause the engine of the car to knock as well. The solution for this problem, if you have a direct injection engine, is to take your car to a shop that is doing carbon cleaning.

They will remove the intake and will release a solution that will dissolve the carbon and they will clean it off with a sucking machine. This procedure is completely safe for your engine and will stop engine knocking.

Rod Knock

A rod knock is something that you clearly don’t want to appear in your engine. A rod knock, as its name implies, is when the rods start to knock against the crankshaft.

This knock appears because the bearings that are between the rods and the crankshaft are diminished in size. The tolerances for the bearings are relatively low and when they wear, that knocking sound will start to appear.

This knocking sound is bad news for you and your engine. What is unique for this sound compared to other engine knocking sounds is that the engine makes it louder. You will basically hear a hard knock when the engine turns over.

With every rotation of the crankshaft, the damage becomes heavier and heavier. This knock will soon ruin your piston rings and the piston will start to rub with the cylinder wall and scar the wall. Also, it can damage the crankshaft if the bearings are too far gone. There will be grooves.

If you have an engine that is knocking, the only solution is to disassemble everything and inspect the damage. If the engine is repairable, then you will most probably need to machine work the block and the crankshaft.

This machine work can cost you up to $2000 since it requires a lot of expertise and not many shops are performing this type of work.

If the repair is too expensive, then it’s better to get a used engine in good condition. This will guarantee you that the engine you are going to install will be perfectly good.

The reason why the rods are starting to knock is the lack of maintenance. The less frequent the oil changes the bigger the chances for the engine to develop rod knock.

How To Fix Engine Knocking

The cost to fix this problem lies in the cause of the problem itself. If it’s caused by low octane gas, then you need to add premium gas to your car and the car will for sure rejuvenate and will work properly once again.

If the problem perhaps lies in the lean air to fuel mixture, then you probably need to play with some of your sensors and start diagnosing the issue with an OBD2 tool. This tool will give you a lot of feedback on your engine health and the possible reasons why the problem occurs.

If it’s a sensor, you need to troubleshoot even deeper and see if it’s good or not. Most of the sensors can be tested with a multimeter. This tool is a lifesaver in these situations. When you have this type of problem, the OBD2 scanner and the multimeter are your best friends.

On the other hand, if the problem is of mechanical nature, you need to see which component is making this sound. If it comes from the valves, then it means that they have to be adjusted. If it’s caused by the lifters, then you will have to replace them.

And in the worst-case scenario, if there is a rod knock, then you will probably need to find a shop that will do the machine work on your engine. Or if the engine is too far gone, then you will have to look for a replacement engine. This can cost a lot, but at the end of the day, it’s a much better solution than rebuilding a damaged engine.

Engine Knocking: What Causes It and How to Fix It

  • Engine knocking happens when fuel burns unevenly in your engine’s cylinders, causing potential damage to your engine’s cylinder walls and pistons.
  • Faulty spark plugs can cause engine knocking, as spark plugs age and break down over time, and if left unreplaced, could lead to a drop in engine power and a loss of fuel economy.
  • Low-octane fuel could lead to excess engine noise, as engines engineered to handle high-octane fuel may not perform well with regular fuel, which could damage your engine and decrease fuel economy.
  • Carbon deposits can form despite the required carbon cleaning detergents in fuel, leading to less room for fuel and air to reside, increasing compression, and leading to nasty knocking sounds.
  • Excess carbon buildup can lead to problems in the combustion process, damage your engine’s cylinders, lower gas mileage, or cause overheating.
  • Checking your owner’s manual for the recommended fuel type and using it can help avoid engine knocking caused by low-octane fuel.
  • Regular tune-ups, including spark plug replacement (which you can learn more of in our guide on how to change spark plugs), can help bring power and efficiency back to your car, potentially preventing engine knocking caused by faulty spark plugs.
  • Having your cylinders cleaned by a professional can help avoid engine knocking caused by carbon deposits.
  • Long-term use of the wrong fuel or ignoring engine knocking could lead to costly engine repairs down the line, making cheaper gasoline not a cost-effective option.
  • If you’re not sure what’s causing the engine knocking, it’s best to bring your car to a professional for inspection and tune-up to prevent further damage to your engine.

Engine Knocking – Conclusion

In this article, we have learned a lot about the engine knocking problem and what is causing it. As we said, there are two probabilities. One of them is caused by detonation-related issues like misfires, lean air to fuel mixture, and bad timing or sensors.

Meanwhile, the mechanical engine knocking is caused by unadjusted valves, lifter tap, carbon buildup, and the worst problem which is the rod knock.

If your engine has a rod knock, the best solution is to look for a good used engine that has a lot of life in it.

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