Are you hearing an annoying, engine knocking, pinging or rattling noise, when you accelerate your engine.
For instance, knocking, when working hard under load, like driving uphill, passing a slowpoke or towing a trailer.
Then, most likely you’re probably experiencing, spark knock. So, what do you think is making that noise.
First, 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.
How To Narrow Down The Causes Of, 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. As, this allows intake vacuum to suck some exhaust in, through the (EGR) valve. Consequently, to dilute the air to fuel mixture slightly. This lowers combustion temperatures, and prevents engine spark knock.
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. If so, 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 Knock Sensor (KS) Is Working
Your engine has a knock sensor (KS), that should detect detonation. And if so, 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 that may occur, when the engine is working hard under load. And then, cause the (PCM) to retard the timing.
This reduces power a bit, but protects your engine against detonation. However, if the knock sensor (KS) is not working, spark timing will not retard when it should. So, 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.
How To Testing The Knock Sensor (KS)
The (KS) can be tested, by tapping on the engine near the (KS) 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 (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. Treat 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. And, stops engine knocking.
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.
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 the engine knocking.
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.
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.
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.
In Summary: Engine Knocking
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.
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 !!
