Engine detonation, otherwise known as knocking or pinging, is either nothing to worry about or a serious warning of catastrophic engine failure. The important thing is knowing how to identify combustion problems as irregular, because the second scenario is a pretty bad one.
The Big Bang
Knocking happens on top of the engine pistons in the chamber during combustion. Under normal operation, a spark is perfectly timed with fuel injection, valve openings and closings and piston location (pressure) to create an explosion in the chamber. The spark plug sending the spark is drilled in at a specific angle, so the explosion hits the top of the piston in a way that utilizes the force to exert a more balanced combustion phase. It is a detonation, but a controlled one. The process requires heat, pressure and fuel.
An engine may knock if it has become very hot or the timing is a bit off. When this happens, the accumulated heat and pressure ignite the surrounding air and fuel at unintended times and in an uncontrolled manner within the chamber. Along with making a pinging sound, this creates a destructive amount of pressure and forces the piston down in a way and time that isn’t in line with how it was designed to operate. If, for instance, the cam or crankshaft aren’t where they need to be when this happens, the pressure from repeated detonations could force damage.
As mentioned earlier, knocking happens from time to time under normal operation, and it’s not a problem. It’s even more common for diesel engines, which rely only on fuel and pressure (no spark) to begin with. Most modern engines have knock sensors, which notice the irregular detonation and address it by either adjusting the timing or adding more fuel to cool the chamber. However, if you hear knocking consistently again and again, you have the start of a major problem and need to take care of it right away. Ill-timed, unbalanced pressure on a piston can cause breakage of rings and muck up your combustion chamber and valve faces to the point of breaking the connecting rods, bending rocker arms, blowing a head gasket and a litany of other serious problems.
Using a higher-octane fuel helps reduce knocking, but unless you have a high-performance or modified engine, you will probably be fine with regular octane levels. If you notice repeated detonation, seek help immediately. A qualified mechanic will be able to perform a pressure test and remove the head to assess the damage. If you hear consistent knocking, you should get this done as soon as possible, or you risk needing a new engine altogether.
While the consequences of engine knocking range in severity, it is always a good idea to consult a professional if the problem persists.
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Photo courtesy of Blair Lampe.
Blair Lampe is a New York-based professional mechanic, blogger, theater technician, and speechwriter. In her downtime she enjoys backpacking wherever her boots will carry her, rock climbing, experimental theatre, a crisp rosé , and showering love on her 2001 Sierra truck.