15/09/2022
Knock knock, who's there? It's your engine, letting you know there's a problem somewhere under the hood.
If the smooth rumble you're used to coming from your engine is replaced with a repetitive tapping or pinging sound that becomes louder and faster as you accelerate, that's a classic sign of engine knock. But "engine knock" can describe a variety of different noises that can each be caused by all sorts of individual problems.
Figuring out the source of the engine knock noise can be tricky! To help you get started, we've listed 6 of the most common causes of engine knock.
1. Detonation Knock: Too Low Octane
When your engine is running smoothly, the air/fuel mixture burns up in a single, controlled detonation inside each cylinder. Detonation knock is a knocking noise that you'll hear when the air fuel mixture in the cylinders is detonating in more than once place at a time.
2. Detonation Knock: Bad Timing
On most modern cars, the timing of the engine that is, at which point in the engine's travel the spark plugs will fire is controlled by the computer. But, if for any reason the spark isn't firing exactly when it should, this can cause multiple detonations in the cylinder, leading to engine knock.
3. Detonation Knock: Lean Air/Fuel Mixture
Problems with the oxygen sensors, fuel injectors, fuel pump or mass airflow sensor can create a lean air/fuel mixture in the engine. A lean air/fuel mixture is one that doesn't have enough fuel and too much air.
4. Detonation Knock: Bad Knock Sensor
Luckily, engine knock isn't a frequent problem with modern cars, because the air/fuel ratio, fuel injectors and timing are all computer controlled. There's even a knock sensor that's designed to detect engine knock and tell the Engine Control Unit, so it can correct the problem automatically.
5. Rod Knock: Worn Bearings
Another type of engine knock is rod knock. As the pistons travel up and down in the engine, they turn the crankshaft which ultimately sends power to the wheels.
6. Bad Belt Tensioners/Pulleys
Another possible source of engine knocking isn't actually coming from the engine itself at all. It could be coming from the accessory belt.