Engine Spark Knock – Those Knocking, Pinging And Rattling Noises

Engine Spark Knock - Those Knocking, Pinging And Rattling Noises
Engine Spark Knock - Those Knocking, Pinging And Rattling Noises

Engine spark knock, sounds like a metallic knocking, pinging or rattling noise, coming from your engine.

Engine spark knock, is usually heard, during moderate to heavy engine acceleration.

And, usually occurs after the engine, has reached or is near normal operating temperature. Also, engine spark knock, similar to pre-ignition, is basically an erratic form of combustion.

Consequently, engine spark knock happens when, the fuel mixture is subjected to either, too much compression heat or both.

So, if your engine is making that annoying knocking, pinging or rattling sound. Then, you’re probably experiencing engine spark knock.

Engine Spark Knock. How Does It Start ?
Engine Spark Knock. How Does It Start ?

Consequently, anytime the combustion chamber pressures, become high enough, abnormal combustion can occur. Eventually, this could lead to a blown head gasket, broken rings, cracked piston lands. And, or flatten your rod bearings.

Engine Spark Knock Damage
Engine Spark Knock Damage

What Are The Other Causes Of, Engine Spark Knock:

  • Faulty (EGR) Valve
  • Knock Sensor Failure
  • Excessive Carbon Buildup
  • Vacuum Leaks
  • Higher That Normal Compression
  • Exhaust Back Pressure
  • Substandard Fuel
  • Excessive Engine Temperatures

Faulty EGR Valve

(EGR) Valve
(EGR) Valve

So, when the engine is accelerating or bogging under load, the (EGR) valve should open. Because, this allows intake vacuum, to suck some exhaust in through the (EGR) valve. Therefore, diluting the air/fuel mixture. Also, this lowers combustion temperatures and prevents knock. Firstly, inspect the operation of the EGR valve and check, for a buildup of carbon deposits. Either, try cleaning off the carbon deposits, or replace the (EGR) valve, if it is defective.

Knock Sensor (KS) Detects Engine Spark Knock

Knock Sensor (KS) Detects Engine Spark Knock
Knock Sensor (KS) Detects Engine Spark Knock

So, your engine has a knock sensor, that detects this noise. Then, tells the computer, to retard the ignition timing. Engine spark knock may occur when, the engine is working hard under load. Consequently, causing the (PCM), to retard the engine timing.

This reduces power a bit, but protects your engine against damage. However, if the knock sensor is not working, spark timing, will not retard when it should. Consequently, you may hear a pinging or rattling noise when, accelerating, driving up a hill, or when engine is lugging.

By tapping on the engine near the sensor, is one way to test it. Next, watch spark timing and/or knock sensor input, on a scan tool. Because, you need to see, if it sends a timing retard signal.

NOTE: Over advanced ignition timing, can also cause the same thing. So, the engine computer, controls ignition timing. As a result, ignition timing, is not adjustable on today’s engines. Consequently, the only way to change the timing advance, would be to flash reprogram the (PCM).

Excessive Carbon Buildup:

Excessive Carbon Buildup On (EGR)
Excessive Carbon Buildup On (EGR)
  • Older high mileage engines
  • Vehicles that never fully warm
  • Only driven short distances

Treating your engine with a carbon cleaner or a fuel system additive, can usually clears this up.

Vacuum Leaks

Vacuum Leaks Can Cause Engine Spark Knock
Vacuum Leaks Can Cause Engine Spark Knock

Vehicle emission systems, may use vacuum to operate switches, solenoids and actuators around the engine:

  • (EGR) valve
  • (MAP) sensor
  • (PCV) valve
  • Purge valve

Vacuum leaks, in any of these components, may cause knocking or pinging. So, check vacuum hoses in these systems, for damage and loose connections.

Higher That Normal Compression

One cause could be an engine that has had, the cylinders bored oversize. This can increase the engine’s static compression ratio. Another could be a cylinder head that has been, resurfaced to restore flatness. This will reduce the volume of the combustion chamber. And, also increase the engine’s, static compression ratio.

These changes will increase engine power. But, can put the engine at risk of spark knock, on regular 87 octane fuel. Furthermore, engines that are supercharged or turbocharged, are also at a much higher risk. This is because, the forced air induction system, increases compression.

Exhaust Back Pressure

High back pressure, is a common exhaust system problem. This may happen because, of a clogged exhaust pipe, catalytic converter or muffler. Consequently, a clogged converter, is the most common cause, of exhaust back pressure buildup. It will restrict engine airflow, causing the engine, to run hotter and lose power. Consequently, leading to pinging or knocking. Most of the time, a catalytic converter will clog up, because of old age, overheating or fuel contamination.

Substandard Fuel

Substandard Fuel
Substandard Fuel

Regular grade gasoline is supposed to have, an octane rating of 87 but, is not always the case. The fix for this is, to try a tank of mid-range or premium gasoline. Premium costs more, but may be required to reduce the knocking. Or, if you always buy gas at the same gas station, try a different gas station. Don’t buy, the cheapest gas you can find.

Any of these could cause engine spark knock:

  • Excessive Engine Temperatures
  • Engine running too hot because of low coolant
  • Cooling fan that isn’t working
  • Plugged radiator
  • Bad water pump
  • Sticking thermostat


So, engine spark knock occurs when, excessive heat and pressure, cause the air/fuel mixture to auto ignite. This produces multiple flame fronts, within the combustion chamber, instead of a single flame front. When these multiple flames collide, they do so with explosive force. Then, produces, a sudden rise in cylinder pressure. Finally, along with this is a sharp metallic pinging or engine knocking noise.

Thank You !