Are you hearing a knocking sound coming from under the hood while driving around in your car? If that’s the case, you should consider visiting a mechanic because several things could be wrong with your vehicle. The best way to describe this sound is to compare it to a rapid metallic knocking sound. It’s also often described as pinging. Depending on the type of malfunction in question, engine knocking can be a sign of a complicated problem that requires the attention of a skilled professional, while in other cases, it might just be a quick fix that you can easily complete by yourself. 

The most common malfunctions associated with loud engine knocking sounds are: bad spark plugs, worn bearings, low octane rated fuel, or even carbon buildup blocking. This article will cover these malfunctions in more detail, so stick around if you want to find out what causes engine knock. 

Worn Rod Bearings

Rod bearings are a vital part of the engine as they are responsible for the smooth movement of the pistons. Bearings allow the pistons to move up and down effortlessly while compressing the air and fuel mixture. That being said, bearings are susceptible to wear and tear, so once they are worn out, they won’t be able to facilitate the smooth movement anymore. Worn out bearings create a gap, which in turn causes the pistons to make a rattling sound. Fixing this kind of malfunction will require professional help because, in order to replace the worn-out rod bearings with new ones, you’ll need to remove several other parts. This can be a longer repair job, so prepare yourself to spend quite some time at the mechanic’s shop.

Carbon Buildup

Modern fuels are much cleaner than they used to be, so carbon buildup is not as a common occurrence as it was back in the day. However, if you’re not doing regular maintenance on your car, carbon deposits may form and lower the efficiency of your engine by clog the spark plugs, valves, and other essential parts. Carbon buildup will affect the combustion process and will lower the efficient burning of fuel. Luckily, there is an easy fix available in the form of fuel injector cleaners designed to get rid of unwanted carbon buildup. 

Bad Spark Plugs

Malfunctioning spark plugs can cause all kinds of issues, including an irritating knocking sound. In some cases, you might have spark plugs that are working just fine but are the not correct model for your engine type. Engine knocking can also occur when the spark plug gap is not too big or too small. In both cases, the easiest fix is to replace the spark plugs with new ones. Just make sure they are the ones recommended by the manufacturer. Finally, the timing at which the spark plugs fire might be incorrect. Since engine timing is controlled by the computer, you’ll need to seek advice from an experienced technician to correct the malfunction. 

Low Octane Rating Fuel

Last but not least, fuel with a lower than recommended octane rating might be the culprit for the engine knocking noise. To put it in simpler terms, the octane rating dictates the fuel’s ability to resist premature detonation when mixing with air in the combustion chamber. Premature detonation causes the odd pinging sound. Again, there is an easy fix for this issue – just use fuel with a higher octane rating, and the engine knocking sound should go away.

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What Causes Engine Knocking