What Is the Difference Between Detonation and Cylinder Knock?

If your car, truck, or C/SUV’s engine has been knocking lately, it’s natural to wonder what is causing it. It’s also natural to be concerned that the cause could damage the engine. Hummel’s Automotive Diagnostics and Repair advises that you are correct to be concerned. We are going to talk about the differences between detonation and cylinder knock below and the reason why cylinder knock can seriously damage your engine.

Causes of Engine Detonation Knock

Detonation knock can be caused by several different things. What we mean by detonation knock is that multiple detonations in your vehicle’s cylinders are what is causing the knocking sounds. In a normal engine, the air and fuel that is placed in each cylinder will explode one time when the spark plugs ignite them. If there is an unusual condition that causes multiple explosions in each cylinder, this is detonation knock. Things that cause detonation knock include

  • A fuel mixture that has too much air and too little fuel in it
  • Gasoline that contains a lower octane rating than what is recommended for your vehicle
  • Malfunctioning spark plugs that are firing more than once

Your vehicle’s engine is actually equipped with a sensor that is engineered to detect when the engine is knocking. Once it picks up on the knocking sounds, it notifies the engine control unit of a knocking problem. The unit then tries to resolve the issue, such as by adding fuel to a lean fuel mixture. A faulty knock sensor can also cause detonation knock indirectly because it is unable to alert the engine control unit that there are multiple fireballs in the cylinders.

Causes of Cylinder Block Knock

Your engine may also be knocking from the cylinder block but for a different reason. Inside each cylinder is a piston that moves up and down. The pistons are attached to rods to facilitate this movement. The rods are attached to bearings that move the rods up and down. The rod bearings can wear out in older automobiles, and this creates a dangerous condition. The rods move the pistons up and down inside the cylinder walls unevenly. Consequently, the pistons crash against the cylinder walls.

Naturally, if left unrepaired, the pistons will eventually damage the cylinder walls, i.e., your vehicle’s cylinder block. You may also end up with a broken rod, and this will render your engine completely inoperable. As such, it’s important to bring your vehicle to Hummel’s Automotive Diagnostics and Repair in St. George, UT, right away if the engine is knocking all the time.


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