What Causes Intermittent Misfiring?

[DeDominic]

Intermittent engine misfiring is primarily caused by faults in the fuel supply, ignition, and intake systems. An engine can only run smoothly when these three factors are met, so misfiring indicates a problem in one of these systems. Below is a detailed explanation of the causes of intermittent misfiring: 1. Ignition system failure: Aging of ignition coils and spark plugs can cause the ignition system of a cylinder to malfunction. Problems with the ignition coil most commonly lead to reduced power and, in severe cases, sudden engine stalling. 2. Fuel injection system failure: Clogged fuel injectors or fuel lines can prevent sufficient fuel from being supplied to the cylinder for combustion, naturally causing the cylinder to fail to operate properly. 3. Excessive spark plug carbon buildup: Long-term poor combustion leads to carbon deposits accumulating on the spark plug ignition point. When these deposits are wetted by fuel, they create a parallel shunt resistance, resulting in spark plug leakage, weak sparking, or even complete spark plug failure.

[Josh]

Last year my car had this same issue - it would suddenly start shaking violently while driving, sounding like a tractor, but then return to normal after a while. This kind of intermittent misfire is most commonly caused by aged spark plugs or excessive carbon buildup leading to unstable ignition. Ignition coil problems are another culprit, especially in older vehicles where coil insulation deteriorates, making them prone to electrical leakage when the engine is hot. Dirty or clogged fuel injectors can also cause uneven fuel supply, resulting in occasional cylinder deactivation. Poor electrical connections are often overlooked - particularly those plugs in the engine compartment that may loosen after prolonged vibration. Sensor failures shouldn't be ruled out either; for instance, unstable signals from the mass airflow sensor can make the ECU miscalculate fuel injection. Finally, check cylinder compression - poor valve sealing could also create this condition.

[AmirMarie]

Over the years in repair work, I've found intermittent misfires mostly occur in the ignition and fuel delivery systems. Worn spark plug electrodes or excessive gaps are the most common causes - recommend inspection/replacement every 30,000 km. Faulty ignition coils are also frequent; testing coil resistance often reveals issues. For fuel injectors, pay attention if internal resistance exceeds 14 ohms, indicating possible internal short. Don't forget to check for high-tension lead leakage - use a spray bottle in darkness to visualize sparks. For wiring, focus on ECU-to-cylinder harnesses as oxidized pins cause signal loss. Also investigate fuel pump pressure - below 3bar may cause unstable delivery. Additionally, dirty crankshaft position sensors can trigger false readings, often resolved by cleaning.

[DelAlessandra]

Engine misfiring is fundamentally caused by combustion issues. The ignition system is the most vulnerable - even minor carbon buildup on spark plugs can lead to unstable arc discharge. Worn fuel injector solenoid valves cause inconsistent fuel delivery, disrupting air-fuel mixture ratios. Intake system leaks introduce excess air that dilutes the mixture, making ignition more difficult. Electrical faults deserve attention - oxygen sensor signal drift can mislead the ECU into improperly adjusting the air-fuel ratio. Low cylinder pressure due to leakage alters compression ratios, directly affecting combustion efficiency. Prolonged low-RPM driving promotes carbon buildup, which periodic high-speed driving can prevent. Aftermarket parts incompatibility often causes ECU control disorders - try restoring factory settings.