What causes the car to feel jerky?
3 Answers
The reason the car feels jerky is due to piston slap, which is an abnormal noise caused by the piston side hitting the cylinder wall. When the direction of the axial force on the piston top changes as the piston moves from the compression stroke to the power stroke, piston slap occurs. Each time the piston passes top dead center and moves downward, it is forced to hit the cylinder wall, leading to piston slap. The determining factor for piston slap is the clearance between the piston and the cylinder wall, commonly referred to as piston clearance. The effect of piston clearance on slap: when the engine is cold, the piston clearance is larger, resulting in louder knocking sounds. However, as the engine temperature rises, the piston clearance decreases accordingly, and the knocking sound diminishes. If piston slap occurs, it is advisable to promptly visit a repair shop for inspection and repair.
I often experience the car jerking, which is usually due to engine misfiring, meaning one of the cylinders isn't firing or isn't firing properly. The most common cause is issues with the spark plugs, such as aging or incorrect gap, leading to reduced ignition capability. A faulty ignition coil can also cause this, especially noticeable during startup or acceleration. It could also be a fuel system problem, like clogged fuel injectors or a weak fuel pump, resulting in uneven fuel spray. If the intake system is dirty or the mass airflow sensor malfunctions, it can affect the air-fuel mixture ratio, causing the car to shake. On the mechanical side, uneven cylinder pressure or a loose timing belt can also lead to this issue. Last time I had my car repaired, replacing the spark plugs solved the problem. If the jerking persists frequently, it could accelerate wear on parts and even increase fuel consumption and safety risks, so it's best to have a professional mechanic check it out promptly.
After years of driving, when my car starts jerking, I know it's mostly an ignition system issue. Worn spark plugs tend to get blackened or develop larger gaps, directly affecting ignition performance; if the ignition coil overheats or cracks, it can cause similar symptoms. Clogged fuel injectors may spray gasoline inaccurately; poor fuel quality or a dirty filter can also contribute to the problem. On the intake side, an unchanged air filter for too long or a leaking pipe can make the air-fuel mixture too lean or rich, causing engine instability. Additionally, sometimes sensors are to blame, like a faulty oxygen sensor misleading the ECU into improper adjustments. I suggest starting with a simple spark plug replacement first. If that doesn't work, then check the electrical circuits. Long-term jerking wastes fuel and damages the engine, so early inspection can save a lot of money.
