Engine Knocking, Pinging, Rattling, Detonation And Spark Knock


Your engine has a knock sensor (KS), that should detect detonation and tell the computer, to retard the ignition timing. If your engine requires premium grade fuel, but you are using regular or mid grade fuel. Then, the knock sensor (KS) should detect any detonation, when the engine is working hard under load. As a result, causing the (PCM) to retard the timing.

Knock Sensors (KS) Bolted To Engine Block
Knock Sensors (KS) Bolted To Engine Block

This reduces power, but protects your engine against detonation and engine failure. But, if the knock sensor (KS) is not working, spark timing will not retard, when it should. Then, you may hear a pinging or rattling sound (spark knock), when accelerating, or driving up a hill. Also, when the engine is lugging, under a heavy load.

Testing The Knock Sensor (KS)

The knock sensor (KS) can be tested, by tapping on the engine near the sensor. You should do this, while watching spark timing and/or knock sensor (KS) input, on a scan tool, to see if it sends a timing retard signal.


NOTE: Over advanced ignition timing, can also cause the same thing (engine spark knock). The only way to change the timing advance, would be to flash reprogram the (PCM).


Excessive Carbon Buildup, In The Combustion Chambers And On The Tops Of The Pistons

This is usually more of an issue, with older engines. This includes vehicles, that are only driven for short trips and never fully warm up. First, try treating the engine, with a dose of top engine cleaner or a fuel system additive. Because, it also helps remove carbon from the combustion chambers.

Carbon Buildup On Top Of Piston
Carbon Buildup On Top Of Piston

Some repair shops, use a machine to perform an engine carbon cleaning procedure. The machine uses, a concentrated detergent to flush out the fuel injection system and combustion chambers.

Compression Ratio Too High

If the cylinder head 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 increase the risk of detonation, on regular 87 octane fuel.

Resurfaced Cylinder Head
Resurfaced Cylinder Head

Such changes may require, using higher octane 89 or 93 octane premium fuel and/or retarding spark timing. Engines that are supercharged or turbocharged are also, at a much higher risk of detonation. Because, the forced air induction system, increases compression. This usually requires, using premium fuel, to stop engine knocking.

Octane Rating
Octane Rating

Using Low Quality Or Cheap Gas

Regular grade gas, is supposed to have an octane rating of 87. But, if the gas station or their refiner is cutting corners and the fuel is not 87, it may knock. The fix for this is, to try a tank of mid range or premium gas.

Low Quality Fuels
Low Quality Fuels

Or, if you always buy gas at the same gas station, try a different gas station. Also, don’t buy the cheapest gas you can find.

Engine Overheating

If the engine is running too hot, it may cause the fuel to detonate.

This may be the result of:

  • Low engine coolant
  • A cooling fan that isn’t working
  • A clogged radiator
  • Bad water pump
  • Sticking thermostat

All adding to, engine knocking.

Automotive Engine Overheating
Automotive Engine Overheating

If you’ve got an overheating problem, and you’ve checked the cooling fan and radiator, plus replaced the thermostat. Then, chances are you’ve got, a failing water pump.




منبع: https://dannysengineportal.com/engine-knocking-pinging-rattling-noise-common-causes/