Rod Knock – Top Symptoms & Causes Rod Knocking in A Truck

What is a rod knock in an engine? If you are a newbie and just getting to know some mechanical things with trucks, or vehicles in general, then this guide is for you. Nobody wishes to hear rod knock from their engines because it results in costly repairs. As you read this guide, you will know its causes and tell when your engine suffers a rod knock.

What is Rod Knock?

Rod knock is a deep sound from your truck’s engine. It results from worn-out rod-bearing. The truck’s connecting rod bearing has more clearing that causes additional movement. When your pistons change their direction, the metals start to heat, resulting in the knocking nose.

Causes of Rod Knock

Worn-out connection rods are the most common cause of rod knock. Here are some other causes of rod knock that you should know.

Worn-out Bearings

The up-and-down motion of the pistons enables the crankshaft to rotate and sends power to the wheels. The bearings ensure that the pistons move in a smooth and controlled manner. However, as time goes by, the bearing starts to wear out, and when this happens, the piston rods will rattle against the crankshaft. You will hear a rod-knocking sound.

Poor Timing 

Poor timing is another reason for the rod knock in the engine. Timing is the period when the computer controls the spark plug to fire. The spark plug is unable to fire at the required time when timing is off, leading to a series of detonations within the cylinders. If this happens, you will hear the detonation knock.

Lean Fuel Air Mixture

You will hear the rod knock when there is a lean fuel-air mixture that is usually caused by defective oxygen sensors, failing fuel injectors, and faulty fuel pumps. You will experience a lean mixture when there is less fuel and too much air in the combustion chamber, which will interfere with the proper combustion.

Faulty Knock Sensor

You will hear the detonation knock when the knock sensors malfunction. This occurs on rare occasions on newer trucks because the fuel-air ratio, fuel injectors, and timing are all computer controlled.

The knock sensor will always detect any issue and signals the ECU, and corrective action is taken immediately.

Symptoms of Rod Knock

There are two main symptoms of rod knock you should know.

Knocking Sounds

The production of a knocking sound is the primary symptom of rod knock. You will hear a loud sound when you start your truck. The sound will be louder as you press the gas pedal.

Low Oil Pressure

Your oil pressure will reduce as soon as the bearings between the piston rods and the crankshaft fail. You will notice this when you are starting your truck.

The check engine oil light will appear on the dashboard, which will notify you that the oil pressure is low. When this light appears and disappears, it strongly indicates that the bearings are completely worn out, and you should consider replacing them before the worst happens.


Rod knock sound is a serious sign you should never ignore when you hear it from your truck. The above are some of the causes and symptoms worth knowing and should help you better maintain the vehicle.

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