Potential Causes Of Spark Knock Within Your Engine’s Cylinders
Potential Causes Of Spark Knock Within Your Engine’s Cylinders
Your engine’s 4-stroke combustion cycle is supposed to be tuned to precision. Air and fuel enter each cylinder’s chamber before being compressed for ignition. A spark ignites the mixture and generates the energy needed to turn the crankshaft. The rotation of the crankshaft moves your vehicle. This cycle occurs thousands of times each minute while you’re on the road. For a variety of reasons, however, the air-fuel mixture may detonate unpredictably. This is a problem known as spark knock (sometimes called detonation).
Spark knock occurs for one of two reasons: the air-fuel mixture is either too compressed or excessive heat is present inside the chamber. The constant detonation will eventually damage your engine and head gasket. In this article, I’ll describe the factors that can contribute to the problem, so you’ll know where to begin troubleshooting.
Failing Knock Sensor
All vehicles are designed with a knock sensor that monitors incidents of detonation. Under normal circumstances, this sensor will detect knocking and report the event to your car’s powertrain control module (PCM). The PCM will adjust the ignition timing in order to minimize – or eliminate – the detonation. In doing so, it helps the engine perform more efficiently.
If the knock sensor fails, it will be unable to alert the PCM that detonation is occurring within the combustion chamber. As a result, the PCM cannot make adjustments to the ignition timing. This allows spark knock to continue damaging the engine.
Failing Exhaust Gas Recirculation (EGR) System
When your engine is operating under load, the EGR valve is supposed to open in order to allow exhaust to escape. By doing this, the EGR valve thins the air-fuel mixture in the combustion chamber. This lowers the temperature inside the chamber, and thus makes detonation less likely.
If the EGR valve fails, it will be unable to open. Consequently, exhaust will not be allowed to escape, and the temperature inside the combustion chamber will remain high. Spark knock thus becomes more likely.
Accumulation Of Carbon Deposits
Carbon can build up inside the combustion chamber and form deposits along the wall and on the piston. This allows heat and compression to rise in the chamber, which raises the risk of detonation. Deposits are most prevalent in cars that are seldom driven over long distances.
Low-Quality Fuel
One of the dangers of using cheap gas in your vehicle is that the stated octane level is often unmet. The fuel’s producers try to keep costs low, and do so in whatever manner is available to them. This includes selling gas with a stated 87 octane that is actually less than 87.
The problem is that 87 is required by most engines to prevent detonation. If there is less octane in the fuel, heat and compression within the combustion chamber rise. This causes spark knock. Usually, transitioning to a high-quality brand of gasoline will get rid of the knocking sound. By then, however, damage to the piston may have already occurred.
Excessive Compression Ratio
Your engine has been designed according to specifications that should normally prevent knocking. The size of the cylinders, the volume inside the chambers, and other aspects help maintain a relatively static compression ratio. When these attributes are modified, however, the compression ratio may rise. For example, this is the case when cylinders are bored in order to accommodate larger pistons.
When the compression ratio rises, spark knock becomes more likely, especially if you continue to use octane 87 fuel. Depending on the modifications, 87 may be insufficient for controlling heat and compression within the chambers. Higher-octane gas is usually required.
The takeaway is that detonation can severely damage your engine, leading to expensive repairs. For this reason, you should have your mechanic find and resolve the underlying cause as quickly as possible. The discussion above provides a good starting place for troubleshooting the problem and taking corrective action.