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What Is Engine Pinging?

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"Pinging" is the rattling sound an engine can make when accelerating. It usually occurs when the vehicle pulls away from a stop and the engine is under a lot of load or is "lugging" This is not a normal condition or desirable condition.

Here are some common reasons for an engine to ping.

An engine can ping because the combustion process is incorrect in some way. A "spark knock" is the result of combustion occurring too early. In a properly-firing cylinder, the flame front starts on one side of the piston and burns across the top to the other side, which creates a rapid and evenly-expanding gas that pushes down on the top of the piston. When the combustion process occurs too early, there is a random explosion in multiple locations on top of the piston; when this occurs, the flame front inside the cylinder collides with itself and does not burn evenly. An ignition timing that is too far advanced from the proper specification will create a spark knock because the combustion is initiated too early. 

An engine can ping because it is too hot; this is another uneven combustion scenario that is caused by the air-to-fuel mixture "lighting off" by itself. If the cooling system does not keep the engine's combustion chamber temperature in check, the air-to-fuel mixture will begin to spontaneously explode. This is also called "pre-ignition."

In addition to cooling system problems, pinging can be caused by improper gasoline octane, an overly lean air-to-fuel mixture, or a lack of proper exhaust gas recirculation. The exhaust gas recirculation system (EGR) was created to neutralize engine pinging by adding a small amount of exhaust gas to the air-to-fuel mixture going in to the combustion process, which limits the peak combustion chamber temperature.

When an engine pings, it releases pollution into the environment in the form of nitrogen oxide (NOx) and raw, unburned hydrocarbons (HCs). These two chemicals are poisonous gases that show up as yellowish-brownish in a polluted sky. They can also cause respiratory problems like asthma and emphysema—a pinging engine is never a good thing.

 

Daniel Dillon has 22 years of experience as a licensed Smog Technician in California. He helped write test questions for the California Smog Technician Exam, and has performed Consumer Assistance Program and gold shield diagnostic work for the state. He also was an instructor for SnapOn Tool Corporation.