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.
Engine spark knock similar to pre-ignition, is basically an erratic form of combustion.
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.
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.
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
When the engine is accelerating or lugging under load the (EGR) valve should open. This allows intake vacuum to suck some exhaust in through the (EGR) valve; to dilute the air/fuel mixture slightly. Also, this lowers combustion temperatures and prevents knock. 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
Your engine has a knock sensor that detects this noise and tells the computer to retard the ignition timing. Engine spark knock may occur when the engine is working hard under load causing the (PCM) to retard 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 sound 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. You need to see if it sends a timing retard signal.
NOTE: Over advanced ignition timing can also cause the same thing. The engine computer controls ignition timing. As a result, ignition timing is not adjustable on today’s engines. The only way to change the timing advance would be to flash reprogram the (PCM).
Excessive Carbon Buildup
- 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.
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. 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, also the risk of engine spark knock on regular 87 octane fuel. 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. As a result, 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 because, of old age overheating or fuel contamination.
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
Finally, 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 that produces a sudden rise in cylinder pressure. Also, along with this is a sharp metallic pinging or knocking noise.
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