Finding A New Car

Why Does Your Engine Produce Knock Sounds?

An engine knock or denotation is one of the unusual sounds your engine produces due to different underlying problems. If you ignore a denotation, your engine could blow up. When you take your vehicle for engine knock auto repairs, your mechanic must first identify the cause of the knock. Discover four causes of engine denotation.

1. The Fuel Has Low Octane or Is Low Quality

Every vehicle has expected fuel octane ratings under which the engine operates efficiently. Check your manual if you aren't sure of your engine's rating. The typical octane ratings for unleaded gasoline are regular (87 percent), mid-grade (89 percent), and premium (91 to 93 percent). Regular has the least rating, hence the least resistance to combustion.

Many cars use regular octane fuel, but if you have a luxurious or high-end car, you will need a higher rating. On the other hand, less-complex vehicles use lower compression engines with low horsepower. So, you don't need a higher octane fuel to avoid engine knock if you have a regular car. But, if your vehicle needs a high octane fuel, a lower quality type doesn't burn with enough uniformity to resist knocks.

2. The Knock Sensor Is Faulty

As the name suggests, knock sensors prevent the occurrence of denotations. Even at inaudible levels, the sensors notify the engine control unit (ECU) if engine knocks occur. Then the ECU takes the necessary corrective measures. For example, it slows the ignition timing to resolve the problem.

A faulty knock sensor cannot detect the denotations. As a result, the engine control module won't get the information to adjust the timing. In other cases, the sensor sends false signals to the control unit, which causes or worsens the denotation.

3. The Combustion Chamber Has Carbon Build-up

Carbon build-up usually stems from poor quality fuel, high mileage, or carbon-based fuels. The carbon generated during normal operations clogs the chambers. The deposits also consume the space your engine needs to mix air and fuel. As the deposits get bigger, the compression in the cylinder rises and causes denotations.

Carbon build-up also makes your vehicle develop hotspots that cause premature ignition by the spark plugs. As a result, the efficiency of the firing and power strokes decline. In other cases, the firing doubles up and goes out of line, thus creating knocks, pings, and rattles.

4. The Bearings Are Worn Out

Your engine has rods or bearings that push the piston up and down to turn the crankshaft and make your car move. Unfortunately, the bearings don't last forever and are bound to fall out of position. Besides, bearings wear out with time due to the numerous rotations your engine pistons make. As a result, you will hear the pistons knock against the crankshaft; hence the denotation sounds.

If you ignore worn-out bearings, the frequent knocks damage the connecting rods and add to your list of repairs. Besides, piston and crankshaft repairs which correct the denotation are intensive.


Engine knocks have different severity based on the problem's cause. Either way, each denotation calls for an immediate auto repair. So if you hear engine knocks or your car develops any other problem, look no further than a local auto repair shop.