What's That Knocking Sound | Blog

A combustion engine is supposed to run smoothly from the moment you turn on the ignition, to the moment you come to a stop. From time to time, your engine might produce an unfamiliar noise that might be difficult to diagnose. Let’s face it; cars make the weirdest noises; squeals clunks, rumbles and roars that are all considered healthy.

However, the moment you hear a knock, you may be dealing with a mechanical problem under the hood that could potentially damage your vehicle if unresolved.

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What is Engine Knocking?

Knocking or pinging in your engine can mean a lot of things. Some are easy to fix, while others may be an indication of major damage. Knocking sounds in your car engine is often an indication that there is an incorrect air-fuel ratio mixture. It forces a chain of reactions where your car’s fuel burns in uneven pockets rather than normally in uniform bursts.

If ignored, this problem could damage the cylinder and piston wall. Knocking will also occur when there is no lubrication on the top part of the cylinder head. It’s normally a ticking sound caused by lifters and valves that are either loose or not receiving sufficient engine oil.

Ideally, the most common cause of engine knocking is related to the engine’s capability to operate efficiently.

What causes an Engine Knock?

Carbon Deposits Resisting Efficient Fuel Burn

All fuel used in vehicles needs a carbon cleaning detergent, however, this doesn’t necessarily mean they will prevent the formation of carbon deposits. When fuel mixes with oxygen, it burns. Since diesel and gasoline consist of multiple carbon molecules, the residual carbon will form on spark plugs, valves, and other components in the combustion chamber. This formation reduces the volume inside the cylinder, decreasing the amount of compression produced. In most scenarios, additives or special fuel injectors can resolve this issue.

Faulty Spark Plugs

Sparks plugs are an integral part of your vehicle’s electrical system. They are what deliver the electric spark that ignites the cylinder’s air/fuel mixture. Your spark plugs are what get your engine running. Over extensive use, your spark plugs will wear out. According to our technicians at AAMCO Boise, new spark plugs need installing every 30,000 miles. It’s also important to note their longevity depends on their condition and type. Your engine could be knocking if you are not using manufacturer recommended spark plugs or your spark plugs are wearing out.

Low Octane Fuel

Your engine could knock in case you are using fuel with an octane rating that is too low for your vehicle. The octane rating is the measure of a fuel type’s ability to resist detonation of the air/fuel mixture in the engine. The combustion process causes pining or knocking sound. To prevent this, the car owner needs to make sure they are using gasoline with an octane fuel rating that is at or above the manufacturer’s recommendation.

Rod Knock

Another type of engine knock is the rod knock. As your engine piston travels up and down in the engine, they turn the crankshaft sending power to the wheels. Rod bearings in the engine facilitate smooth piston movement, but over time, they may get worn or come out. When the bearings begin to wear out, the pistons will start to rattle against the crankshaft, producing something similar to a knocking sound. Fixing this problem needs new bearings, as well as work on the piston and crankshaft- which is a time-intensive and expensive repair.

Detonation Knock: Bad timing

On modern vehicles, the timing of the engine (the point in the engine’s travel where the spark plugs will fire) is normally controlled by a computer. Therefore, if, for any reason, the spark is not firing when it should, it could result in multiple detonations in the cylinder, leading to a knock.

AAMCO Boise Engine Repair Service

If your car’s engine is knocking, it’s best to stop by your nearest AAMCO Boise auto care center and have our mechanics get to the bottom of the noise. Depending on your car, age, make, and model, a simple tune-up might be all you need. We also offer other auto care services, including transmission maintenance and service, car engine repair, brake service, suspension service, and maintenance, regular car maintenance, and many more.

Schedule an engine inspection service with us today! Its time to get your engine riding smooth again.

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