What Causes Intermittent Engine Misfire?

[ODaniel]

Engine misfire can be caused by various factors including the mechanical system, fuel system, intake system, ignition system, and electronic control system of the engine. Symptoms of engine misfire: Abnormal engine operation or insufficient power, uneven engine performance with rhythmic vibration at high, medium, and low speeds, black smoke and backfiring from the muffler. Hazards of engine misfire: Running an engine with misfire can cause significant damage. Firstly, it increases fuel consumption and emission pollution. Secondly, fuel may enter the oil pan, contaminating the lubricating oil and shortening its service life, while accelerating wear on moving parts. Additionally, unburned fuel may combust in the exhaust pipe, damaging the three-way catalytic converter.

[HaleyMarie]

I've encountered this issue too. The engine misfires sometimes but not always, which is really annoying when driving. It's most likely a problem with the ignition coil or spark plugs. These components tend to wear out over time, especially when the internal wiring of the ignition coil develops poor contact. It may work fine when the engine is cold, but as the engine heats up and the wires expand, problems can occur. Another possibility is worn high-voltage wiring causing a short circuit, which is more likely to happen on humid or rainy days. Insufficient cylinder pressure could also be a reason, such as poor valve sealing or worn piston rings leading to pressure fluctuations in a particular cylinder. This requires professional equipment to measure cylinder pressure for confirmation. Lastly, a clogged fuel injector might cause these intermittent symptoms, especially if there are impurities in the gasoline. I recommend first checking the condition of the spark plugs—replacing them with new ones is inexpensive and worth a try. If that doesn't solve the problem, then test the ignition coil. Don't delay too long, as it could damage the engine.

[LeEverett]

I have experience with this issue. Intermittent engine misfires are often related to wiring problems. For example, if the main harness connector is aged or loose, the connection may become intermittent when the car bumps around—this is quite common in older models. Excessive spark plug gap or severe carbon buildup can also cause unstable ignition, especially noticeable during cold starts in winter. Additionally, a dirty or faulty crankshaft position sensor can lead to inaccurate readings, causing the ECU to send incorrect ignition commands—this can be identified by scanning for trouble codes with an OBD scanner. Don’t overlook the fuel system either; unstable fuel pump pressure or a partially clogged filter causing uneven fuel delivery can also trigger misfires. If it’s just an occasional issue, be sure to check before a long highway drive, as breaking down midway is too dangerous. If you’re handy, you can inspect wiring connectors for corrosion yourself, but for other cases, it’s best to visit a professional repair shop.

[McGriffin]

Sudden engine misfire that recovers on its own is mostly caused by failing spark plugs or a deteriorating ignition coil. My previous car had this issue - it ran fine in city driving but vibrated on highways. Upon disassembly, we found severe electrode erosion on one cylinder's spark plug, causing intermittent ignition due to excessive gap. Poor fuel quality can also clog injectors, leading to fuel delivery issues. Carbon buildup is another common cause, especially valve deposits that disrupt even air intake. Try replacing the spark plug first - it's just a few dozen yuan. If that doesn't work, check the injectors and carbon buildup; a few hundred yuan for cleaning should suffice. Always use gasoline from reputable stations and regularly use fuel additives for prevention.

[VanKhloe]

This issue must be taken seriously. Repeated engine misfiring is very dangerous. Sudden misfiring while driving uphill or overtaking can lead to insufficient power and potential accidents. The causes vary: spark plugs may have reached the end of their lifespan with burned electrodes, high-voltage wires may have damaged insulation causing leakage, ignition coils may degrade in performance when the engine is hot, or the fuel pump may supply fuel unevenly. More troublesome issues include problems with valve lifters or slight leaks in the cylinder gasket, causing fluctuating pressure in a cylinder. Long-term neglect can increase fuel consumption and damage the catalytic converter. I recommend stopping immediately to check: start the engine and listen for intermittent clicking sounds, then lightly press the accelerator to see if the RPM fluctuates. If any abnormalities are found, take it for repair immediately—do not continue driving. Regular maintenance should include oil changes and cleaning carbon deposits from the throttle body.