When you start your car each morning, you may have your mind on many things. Taking the kids to school. The meeting you have after lunch. The book club you enjoy once a month.
But then you hear a strange noise from underneath the hood of your vehicle. What’s that knocking noise? Should you drive your car? Should you call in a tow truck and start rescheduling your day?
How an engine works
Our modern-day engines work in a four-movement process: intake, compression, power, exhaust.
First, air and fuel move into the engine compartment and start the process. Combustion starts as the spark plug and ignition create enough pressure at maximum efficiency. A mixture of fuel/air burns, causing gasses to expand and push pistons downwards rapidly. Pressure rises to peak, until the exhaust valve opens and the piston retracts to eliminate the burned gas.
This process can work perfectly over and over again. Until one day, something goes wrong.
What causes engine knocking
There are a handful of causes for engine knocking. The most common include:
Wrong fuel type
Your car’s engine was designed to operate with a specific octane level. If you hear the engine knocking as you accelerate, it’s most likely caused by having the wrong fuel, specifically with a lower octane level than as designed.
You may have refueled with the wrong gas type. Or the gas station had bad fuel in the tanks. Either way, you have fuel with a low octane in your fuel tank, causing premature combustion. This will cause the engine to knock.
If the issue occurs suddenly after refilling, you can fix the problem on your next refueling. Or you could try using an octane booster to raise the octane level up again.
Bad knock sensor
Your vehicle has many sensors throughout to keep the various systems in check. A knock sensor is designed to prevent engine knock.
An engine strives for maximum performance. The control system pushes for advanced ignition to reach for better performance. If the octane level of the fuel source doesn’t meet expectations, the engine will require a slower ignition process to operate without engine knock. The knock sensor’s job is to monitor for any knocks, and if one occurs, to slow down the ignition process to prevent engine damage.
If the knock sensor goes bad, this control process is no longer in place. This means it could be sending false signals to the engine control, creating an ignition process out of correct timing. Either way, it can cause damage to various components inside the engine.
Incorrect engine timing
Depending on the age of your vehicle, a faulty ignition timing could cause engine knock on an older vehicle.
Newer cars control the ignition timing electronically, so the process is controlled by a sensor, and you won’t be able to adjust the timing.
On an older car, you may have an adjustable ignition timing on either the distributor, an adjustable cam, or crankshaft position sensor. An ignition timing light is used to check the timing. Your owner’s manual will have more information on setting the timing properly. Of course, it’s something you can bring your vehicle in for, and we’ll ensure it’s working optimally.
Lean fuel/air mixture
The fuel/air mixture circulates through various components inside the engine compartment. It heats up in the engine while cooling down in the combustion chamber. If the fuel/air mixture is too lean, it loses its cooling capabilities and will cause the combustion chamber to overheat.
This heat can cause the fuel/air mixture to ignite prematurely before the spark plug delivers a spark. This can cause the engine to knock. This is dangerous for the engine because of how it delivers heat. It can be hazardous for many components, even causing the pistons to melt down over time.
Incorrect spark plugs
While not common, occasionally, the wrong spark plugs may be installed. If they aren’t functioning correctly, they won’t produce the spark necessary at the right time.
If you’ve recently changed your spark plugs and notice engine knock, a quick check will ensure you have installed the correct spark plugs.
If you only hear a knocking sound when accelerating, chances are it’s engine knock. If you consistently hear the noise at other times, it may be something else.
This is when you should bring your vehicle in for a complete inspection, as the problem may stem from timing belt issues, bad rod bearings, or a faulty fuel injector.
How to fix engine knock
The good news is engine knock is fairly easy to fix.
The first step is to determine when the engine knock started. If it was after your last fill-up, it’s most likely from filling up your tank with gasoline. To fix it, you can try an octane booster, or replace the fuel currently in the system.
You can also check the spark plugs if they were recently changed. While not a common reason for engine knock, it does occasionally happen. Be sure the spark plugs installed are specifically designed for your make and model.
If you have an older car with an adjustable ignition timing, check the timing and adjust it as needed. You can check your owner’s manual to find out if you have this system in place.
If you just aren’t sure or prefer to get a professional’s take on what’s happening with your car, bringing it in for an inspection can help get to the root of the problem. A diagnostic scanner can pinpoint where the problem lies, providing trouble codes to help you determine what to fix. A professional will have the right tools for the job, and be able to fix the problem and get you back on the road quickly.
Have you experienced engine knock?
The best way to ensure your vehicle stays operating well is to provide the necessary fluids and components for each system.
Fill your tank from a reputable source.
Ensure spark plugs fit your make and model.
And when you hear any noise out of the ordinary, the quicker you bring it in for inspection, the better chance you have of stopping the problem before it escalates.
How can we help you keep your car’s engine healthy?