What are the common faults of automobile spark plugs?

Update:03 Sep, 2025

1. Spark Plug Carbon Deposits
Symptom: Black, dry carbon dust covers the electrode and insulator skirt.
Causes:
Overly rich mixture (air-fuel ratio imbalance);
Extended, low-speed, short-distance driving;
Insufficient ignition energy (e.g., aging high-voltage wires);
Oil leaking into the combustion chamber (piston ring wear or valve seal leakage).
Impact: Reduced ignition energy, leading to starting difficulties, idling jitter, and increased fuel consumption.

2. Spark Plug Oil Contamination
Symptom: Wet, oily stains on the electrode and insulator surfaces.
Causes:
Engine oil burning (piston ring/valve guide wear);
New vehicle run-in period or severe cylinder wall wear.
Impact: Spark plug short circuit, ignition failure, and possibly blue smoke from the exhaust pipe.

3. Electrode Ablation
Symptom: Severe electrode wear, rounding, or ablation deformation. Causes:
Spark plug heat value mismatch (e.g., low heat value plug used in a high-rpm engine);
Ignition advance angle is too large;
Prolonged high-load operation (e.g., aggressive driving).
Impact: Excessive ignition gap, leading to misfire and reduced power.

4. Ceramic Insulator Crack
Symptom: Cracks or breakage in the insulator.
Causes:
Excessive force during installation;
Thermal shock (e.g., rapid cooling/heating);
Poor-quality spark plug or mechanical damage.
Impact: High-voltage leakage, leading to cylinder failure and engine jitter.

5. Spark Plug Melt
Symptom: Partial melting of the electrode or insulator.
Causes:
Pre-ignition or detonation (low fuel octane);
Premature ignition timing;
Poor heat dissipation (e.g., engine overheating).
Impact: In severe cases, debris can fall into the cylinder, potentially damaging the cylinder wall.

6. Abnormal Spark Plug Gap
Normal gap: Typically 0.7-1.1mm (refer to the vehicle manual for details). Problem:
Gap too large: Insufficient ignition energy, resulting in misfire at high speeds.
Gap too small: Weak spark, incomplete combustion.
Cause: Long-term use without adjustment or electrode erosion.

Summary of automobile spark plug failure symptoms

Symptoms	Possible Causes	Solutions
Difficult Starting	1. Severe Spark Plug Carbon Deposits	1. Clean or Replace Spark Plug
	2. Electrode Gap Excessively Large/Too Small	2. Adjust Gap to Standard
	3. Spark Plug Aged or Damaged	3. Replace Spark Plug
Idle Jitter	1. Single-Cylinder Misfire (Spark Plug Failure)	1. Check and Replace the Faulty Spark Plug
	2. Carbon Deposits Lead to Ignition Instability	2. Clean Carbon Deposits
	3. Inappropriate Spark Plug Model	3. Replace with the Correct Spark Plug Model
Weak Acceleration	1. Electrode Burnout	1. Replace Spark Plug
	2. Inappropriate Spark Plug Heat Value	2. Select the Appropriate Heat Value
	3. Insufficient High-Voltage Ignition Energy	3. Check the Ignition Coil/High-Voltage Wire
Abnormally Increased Fuel Consumption	1. Incomplete Combustion Due to Carbon Deposits	1. Clean or replace the spark plugs. 2. Adjust the gap. 3. Check the ECU and ignition timing.
	2. Abnormal Spark Plug Gap
	3. Delayed Ignition Timing
Engine knock	1. Spark plug heat value too low (overheating). 2. Electrode melt. 3. Preignition caused by low-quality fuel.	1. Replace spark plugs with higher heat value. 2. Check the engine cooling system. 3. Use higher-octane fuel.
Black smoke from the exhaust pipe	1. Carbon deposits on the spark plugs lead to incomplete combustion of the mixture.	1. Clean or replace the spark plugs. 2. Check the air-fuel ratio (oxygen sensor/fuel injector).
Blue smoke from the exhaust pipe	1. Grease on the spark plugs (oil entering the combustion chamber). 2. Damaged piston rings or valve seals.	1. Replace the spark plugs. 2. Repair engine mechanical components (such as replacing oil seals).
Intermittent misfires.	1. Spark plug insulator cracks and leakage. 2. Deterioration of the high-voltage wire.	1. Replace the spark plugs. 2. Check the high-voltage wires/ignition coils.
Jitter after cold start.	1. Spark plug performance deteriorates (poor ignition at low temperatures).	1. Replace with platinum/iridium spark plugs (for better low-temperature performance).