Engine Knocking – Pinging – Rattling Noise – Most Common Causes

Engine Knocking - Pinging - Rattling Noise - Most Common Causes
Engine Knocking - Pinging - Rattling Noise - Most Common Causes

Are you hearing an annoying, engine knocking, pinging or rattling noise, when you accelerate your engine.

For instance, engine knocking, when working hard under load, like driving uphill, passing a slowpoke or towing a trailer.

Then, most likely you’re probably experiencing, engine spark knock (engine knocking). So, what do you think, is making that engine knocking noise.

So, engine knocking, is not necessarily a problem, with your fuel delivery system.

But, it does mean, that your fuel is detonating, or exploding erratically, rather than burning smoothly as it should. Eventually, this could lead to a failed head gasket, broken rings, cracked piston lands and/or flatten your rod bearings.

Abbreviations, that will be used in this Blog Post will include:

  • Exhaust Gas Recirculation (EGR)
  • Knock Sensor (KS)
  • Powertrain Control Module (PCM)

Thankfully, There Are Ways To Narrow Down, The Engine Knocking Noise:

First, Check If The (EGR) Valve Is Working Properly

The (EGR) valve should open when ? The engine is accelerating or lugging under a load. Because, this allows intake vacuum, to suck some exhaust in, through the (EGR) valve. Consequently, to dilute the air/fuel mixture slightly. This lowers combustion temperatures and prevents, engine spark knock.

(EGR) Valve
(EGR) Valve

Inspect the operation of the (EGR) valve and check for, a buildup of carbon deposits. Usually, on the valve pintle or valve port, that may be, blocking the flow of exhaust, back into the engine. Clean off the carbon deposits with a wire brush and carburetor cleaner. Then, replace the (EGR) valve if it is defective.

Next, Check If The Engine Knock Sensor (KS) Is Working

Your engine has a (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 should detect any detonation that may occur when, the engine is working hard under load. And, cause the (PCM) to retard timing.

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

This reduces power a bit, but protects your engine against detonation. 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 (spark knock). Most often, when accelerating, driving up a hill or when, the engine is lugging under a heavy load.

Testing The Knock Sensor (KS)

The (KS) can be tested, by tapping on the engine near the sensor. You should do this, while watching spark timing and/or (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. Treating the engine, with a dose of top cleaner or a fuel system additive. Especially one that also removes carbon from the combustion chamber, usually clears this up.

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 the risk of detonation, on regular 87 octane fuel.

Resurfaced Cylinder Head
Resurfaced Cylinder Head

Such modifications 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 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 gasoline, 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 gasoline.

Low Quality Or Cheap Gas
Low Quality Or Cheap Gas

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, because of:

  • A low coolant level
  • Cooling fan that isn’t working
  • A clogged radiator
  • Bad water pump
  • Sticking thermostat

Then, it may cause the fuel to detonate. Causing, engine knocking.

Overheating Engine
Overheating Engine

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


So, spark knock (detonation), is an erratic form of combustion. And, usually occurs when multiple flame fronts occur, simultaneously inside a combustion chamber. Detonation occurs, because fuel is subjected to either too much pressure, too much heat or both.

Pinging From Low-Octane Fuel
Pinging From Low-Octane Fuel

So, instead of a single flame front growing outward smoothly, like an expanding balloon from the point of ignition. Now, multiple flame fronts are generated spontaneously, throughout the combustion chamber. Then, the fuel automatically ignites from heat and pressure. Finally, the multiple flame fronts collide, creating shock waves that, produce a sharp metallic pinging or knocking noise.

Thank You !