Spark Knock is usually a knocking, rattling or pinging noise which may be heard when he engine is accelerating or is doing work really hard below load (driving up a hill, towing a trailer, passing within the highway, and so on.). Spark knock implies the fuel is detonating.

Detonation is if the fuel explodes erratically instead of burning smoothly. It takes place when there is certainly an excessive amount of heat and compression in the combustion chamber. It is equivalent to preignition, but preignition is once the fuel ignites ahead of the spark takes place as a result of a hot spot within the combustion chamber. Preignition can burn off a hole appropriate throughout the top of a piston (see photo above).

Detonation is incredibly poor for the engine simply because in excess of a prolonged time period it could result in the head gasket to fail, the rings to break, piston lands to crack and/or rod bearing harm.


The points that commonly induce spark knock (detonation) are:

(1) The EGR valve that is not doing work. The EGR valve is supposed to open if the engine is accelerating or lugging underneath a load. This enables intake vacuum to suck some exhaust in through the EGR valve to dilute the air/fuel mixture somewhat. This lowers combustion temperatures and prevents knock. Examine the operation with the EGR valve, and examine to get a buildup of carbon deposits around the valve pintle or valve port that could be blocking the flow of exhaust back in to the engine. Clean off the carbon deposits having a wire brush and carburetor cleaner, or change the EGR valve if it’s defective.

(2) A undesirable knock sensor. Your engine features a knock sensor that must detect detonation and inform the computer to retard the ignition timing. In case your engine calls for premium grade fuel, but you happen to be making use of frequent or mid-grade fuel, the knock sensor ought to detect any detonation which could take place once the engine is doing work hard beneath a load and result in the PCM to retard timing. This decreases power a tiny bit but protects your engine against detonation. Even so, in case the knock sensor isn’t working, spark timing will not retard when it must. As a result, you could possibly hear a pinging or rattling sound (spark knock) when accelerating, driving up a hill, or once the engine is lugging below a heavy load.

The knock sensor may be tested by tapping on the engine near the sensor (not the sensor itself) with a wrench whilst watching spark timing and/or knock sensor input on a scan tool to see if it sends a timing retard signal.

NOTE: Overadvanted ignition timing may also cause exactly the same point (spark knock). But on most late model engines, ignition timing isn’t adjustable and is controlled with the engine computer. The only method to adjust the timing advance can be to flash reprogram the PCM.

(3) Extreme carbon buildup inside the combustion chambers and to the tops with the pistons. This really is typically a lot more of an issue with older, substantial mileage engines or vehicles that are only driven for short trips and never ever fully warm up. Treating the engine using a dose of top rated cleaner or perhaps a fuel system additive that also removes carbon in the combustion chamber can ordinarily clears this up. Some repair shops use a machine identified as a MotorVac to perform an engine carbon cleansing procedure. The machine utilizes a concentrated detergent to flush out the fuel injection system and combustion chambers.

(4) Compression ratio too higher. If an engine has become rebuilt and the cylinders are bored to oversize, it should boost the engine’s static compression ratio. Or, should the cylinder head has been resurfaced to restore flatness, this may decrease the volume from the combustion chamber as well as enhance the engine’s static compression ratio. These alterations will increase engine power, but also the potential risk of detonation on regular 87 octane fuel. Such modifications may demand working with increased octane 89 or 93 octane premium fuel and/or retarding spark timing. Engines that happen to be supercharged or turbocharged can also be at a lot greater threat of detonation because the forced air induction system raises compression. This normally needs using premium fuel.

(5) Inexpensive gas. Standard grade gasoline is supposed to have an octane rating of 87. Should the gas station or their refiner is cutting corners plus the fuel just isn’t 87, it might knock. The repair for that is to attempt a tank of mid-range or premium gasoline. Be warned, however, that some stations cheat on this as well, and don’t always present you with the octane rating claimed around the pump. Premium expenditures extra, but could be essential to cut back the knocking. Or, if you usually buy fuel with the similar gas station, try out a various fuel station. Don’t get the most affordable gasoline you can discover. BP, Shell and Mobil are all fantastic brands.

(6) Engine overheating. In case the engine is operating too hot because of low coolant, a cooling fan that is not doing work, a plugged radiator, negative water pump, sticking thermostat, etc., it could trigger the fuel to detonate.