Things that Cause Knocking Noise from Vehicle When Accelerating - Toyota Service Information To Know in Salem, OR

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 six of the most common causes of engine knock below. When you need this problem fixed, turn to the pros at the Capitol Toyota service department. Our friendly service advisors, skilled technicians and well-equipped facilities mean we can take better care of your Toyota than anyone else in Salem. You know what they say: don't knock it 'til you've tried it!

With this cutaway engine, we can see where the piston is in the cylinder where engine knock often occurs.

6. Detonation Knock: Too Low Octane

First, we need to know what detonation knock is. 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. Parts of the air/fuel mixture can start to ignite too early. When these mini fireballs collide, they create a knocking noise.

If your car has a performance-tuned engine rated for high-octane fuels, you could experience engine knock if you put in fuel with too low of an octane rating. High octane fuels burn more uniformly and resist knock. So, if you put regular unleaded in your car that demands premium fuel, this could be the source of your knocking sound. Be sure to check your owner's manual to find out what octane rating is right for your car.

These spark plugs have been taken out of the engine so they can be replaced.

5. 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.

4. 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. Without enough fuel in each cylinder, the mixture won't burn fast enough, allowing for multiple detonations -- that's engine knock.

This photo shows how the accesory belt winds around various pulleys on the engine.

3. 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.

This naturally means that a bad knock sensor can allow the engine to knock. If you're driving around in a modern car with engine knock, checking the knock sensor is an important part of the diagnostic process.

2. 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. The rod bearings facilitate smooth piston movement, but they can become worn out or come out of position over time. As the bearings wear out, the pistons will start to rattle against the crankshaft, creating a very similar knocking sound. To fix this problem, you may need new bearings or other work done on the pistons or crankshaft -- parts located deep in the engine, meaning this can be a time-intensive repair.

1. 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. As the engine runs, it turns a belt that's connected to various pulleys throughout the engine bay. This belt must be under the exact right amount of tension so that it turns smoothly and quietly. If the belt becomes stretched out, the tensioner isn't working properly, or one of the pulleys becomes bent out of shape, you can hear rattling, clicking and slapping noises that might be mistaken for engine knock. Luckily, fixing a noisy accessory belt can be as simple as replacing the belt, adjusting the tension or replacing a bad tensioner or accessory pulley. We'd be thrilled to help you out with this or any service at the Capitol Toyota service department.

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  1. Capitol Toyota

    783 Auto Group Avenue
    Salem, OR 97301

    • Sales: (888) 459-7024

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Capitol Toyota

783 Auto Group Avenue Ne
Directions Salem, OR 97301

  • Sales: 503-399-1011
  • Service: 503-399-1011
  • Parts: 503-399-1011