An engine misfire is a malfunction, during which one or more of its cylinders are not working. It causes excessive wear and overheating of the engine, and leads to scuffing of the surfaces of pistons and cylinders. In the following we’ll explain how to recognize this problem and how to fix it.
Five signs of malfunction
- Engine jerks at idle. Sometimes the vibrations are so strong that you can feel them in the steering wheel, gear lever, and car body. In addition, the idling rotational speed of the engine is unstable.
- Reduced engine power. You may particularly notice malfunctions in engine operation when you press the accelerator pedal, as well as jerks on acceleration. The ‘Check Engine’ indicator may light up on the dashboard.
- Carbon deposits on the spark plugs and cracks in the high-voltage wires. These are usually easy to spot when inspecting parts.
- Unusual sounds when the engine is running. For instance, intermittent sounds can be heard instead of a steady hum.
- Increased fuel consumption. This is typically caused by problems with the fuel mixing and ignition processes.
Three causes of engine misfire
- Problems in the ignition system. Faulty spark plugs, broken coils and high-voltage wires, or incorrect settings can cause the ignition to fire too early or too late, which in turn disrupts the combustion process of the fuel-air mixture and leads to engine malfunction.
- Disruption of the fuel supply and mixing processes. Soiling of the fuel injectors and malfunction of solenoid valves, clogging of the air filter, leaks in the intake or fuel supply systems or brake vacuum booster can cause a lean or rich air/fuel mixture, which affects combustion efficiency. Failure of the mass airflow sensor, throttle position sensor, or idle air control valve has similar consequences.
- Combustion chamber leakage. This is usually caused by the burning of the valves, pistons, cylinder head gasket, and scuffing on the cylinder surface. It can also be caused by incorrect valve adjustment, faulty tappets or hydraulic tappets, or incorrect valve timing.
Six tips from AUTODOC
- Replace consumables on time. For instance, air filters should be replaced every 10,000–15,000km. Depending on the type, spark plugs last 30,000–100,000 km and fuel nozzles 100,000–120,000 km.
- Clean fuel injectors regularly, around once a year. Do this by adding a special additive to the fuel. In case of significant soiling, you should visit a service station.
- Use high-quality motor oil only. The products of engine wear can cause engine overheating, piston ring jamming, and destruction of elements. It is recommended to change the lubricating material and oil filter every 10,000–15,000 km.
- Use high-quality fuel. This will prevent the build-up of carbon on the surfaces of the engine components.
- Let the engine run at the highest rpm from time to time. This will briefly increase the temperature in the combustion chambers to 500°С and clean the tips of the spark plugs of deposits.
- When servicing the engine, tighten all threaded connections with the torque specified in the car’s technical documentation. This will ensure the leak-tightness of all joints and the integrity of sealing elements.
Conclusion
An engine misfiring not only affects its performance, but is also a symptom of serious defects. That’s why it’s important to perform thorough diagnostics of the engine at the first sign of a problem and repair the fault as soon as possible. Timely engine servicing ensures long, trouble-free operation.
Den: a smiley technician with plenty of experience starring in AUTODOC’s video tutorials. Never seen without his goggles. Races his BMW X5 E53. Dreams about receiving a Gold Play Button for getting 1,000,000 subscribers on YouTube.
