How to Diagnose Faults by Checking Spark Plugs?

Inspecting automotive spark plugs is a very practical way to diagnose problems because they directly reflect the engine's operating condition and combustion efficiency. Observing the condition of the spark plugs can help us discover potential engine issues.

1. Abnormal Spark Plug Color

The color of the spark plug electrodes and ceramic insulator can reveal the engine's combustion status. Different colors usually correspond to different types of problems:
Normal Spark Plug Color: Spark plug electrodes and insulators are usually light brown or gray, indicating good combustion and normal air-fuel mixture and ignition.
White/Gray Burnt: If white or gray burnt marks appear on the spark plug electrodes, it usually indicates engine overheating, possibly due to over-ignition or cooling system problems (such as insufficient coolant).
Black Carbon Deposits: Excessive black carbon deposits on the spark plugs may indicate excessive fuel, incomplete ignition, or spark plug damage. This phenomenon is common in cases of uneven fuel injection or a dirty air filter.
Oil Stains: If there are obvious oil stains (such as wet oil stains) on the spark plugs, it indicates excessive engine oil consumption, which may be due to poor piston ring or valve sealing.

2. Spark Plug Electrode Wear

Spark plug electrodes wear down over time, increasing the gap between them and affecting ignition performance.
You can check the degree of electrode wear:
Excessive Electrode Wear: If the electrodes are worn excessively, the spark plug cannot provide a strong enough spark, which may cause difficulty starting the engine, vibration, or reduced power. The spark plug needs to be replaced.
Uneven Electrode Erosion: Uneven electrode erosion may be caused by a malfunctioning ignition system or poor fuel quality.

3. Spark Plug Carbon Deposits or Stalling

If there is obvious carbon buildup on the spark plug surface or the engine stalls, it may indicate the following problems:
Incomplete Combustion: Carbon buildup on the spark plugs may indicate an overly rich air-fuel mixture or incorrect ignition timing.
Excessive Short-Distance Driving: Short-distance driving can lead to insufficient engine temperature, resulting in low spark plug temperature and incomplete carbon burn-off. Unstable ignition: If the spark plug electrodes show signs of stalling, it may indicate a problem with the ignition system, such as a faulty ignition coil or inaccurate ignition timing.

4. Damaged spark plug electrodes

Physical damage to the spark plug electrodes (such as breakage or detachment) may be caused by excessive engine vibration or a quality issue with the spark plug itself. If a broken electrode is found, the spark plug must be replaced immediately.

5. Check spark plug gap

An improper spark plug gap can lead to poor ignition and affect engine performance. A spark plug gap gauge can be used to check the electrode gap to ensure it meets the manufacturer's specifications.
Gap too small: This can cause difficulty in ignition, poor engine starting, or unstable engine operation.
Gap too large: This weakens the energy for spark ignition, potentially leading to incomplete combustion and reduced power.

6. Common causes of spark plug damage

In addition to wear, carbon buildup, and oil contamination mentioned above, spark plug damage can also be caused by:
Overvoltage: Excessive voltage in the ignition system can damage the spark plugs.
Incorrect ignition timing: Incorrect ignition timing can also cause spark plug damage or abnormal performance.
Incompatible spark plug specifications: Using unsuitable spark plugs can lead to ignition problems.

7. How to use spark plugs for diagnosis

Checking the condition of spark plugs can help diagnose some common engine problems:
Difficulty starting or engine instability: Check the spark plugs; excessive electrode wear or severe carbon buildup can cause poor ignition.
High fuel consumption or weak acceleration: Black carbon buildup on the spark plugs may indicate excessive fuel or incomplete combustion.
Engine overheating or abnormal performance: White burnt marks indicate potential cooling system problems or excessively high combustion temperatures.

By checking the spark plugs, we can effectively diagnose the engine's operating condition. Changes in the appearance of the spark plugs can reflect problems such as overheating, incomplete combustion, and excessive carbon buildup. If abnormal signs are found in the spark plugs, timely replacement and inspection of other related components (such as the ignition system and fuel system) can ensure the normal operation of the engine.