Breakdown of high voltage on the engine body or adjacent elements is often accompanied by a characteristic crack under the hood, which is especially clearly audible in wet weather or when the lights are turned on. This phenomenon occurs when dielectricity The candle insulator or high-voltage wire is reduced to a critical level, allowing the electrical discharge to find the path of least resistance. As a result, the spark skips not between the electrodes inside the combustion chamber, but outside, which leads to the failure of the ignition of the fuel-air mixture in a particular cylinder.
Visually determine the location of the current leakage can be in complete darkness: with the engine running in the area of candle wells will be noticeable bright blue-purple flashes. This behavior of the electrical system not only causes unstable operation of the power unit, but can also lead to failure. ignition Or coils because of the increased load. Ignoring the first signs of breakdown is fraught with serious financial costs for repairing the ignition system.
The main cause of external discharges is a violation of the integrity of the ceramic insulator or the ingress of moisture and oil into the candle well. When conductive carbon or technical fluid settles on the surface of the ceramic, the resistance to insulation drops, and a high voltage of tens of thousands of volts rushes to the “mass”. Drivers need to understand that even a microscopic crack in the ceramics, invisible on a cursory inspection, can become a channel for energy leakage.
Physics of the process and the main causes of failure
Electrical breakdown occurs when the electric field strength exceeds the strength limit of the insulating material. In the ignition system of the car, the voltage in the secondary coil can reach 20-30 kV or more. If high-voltage or the case of the candle have defects, the current will not go to the central electrode, but will close to the nearest metal part of the engine. This physical phenomenon explains why the engine starts to work under load or in wet weather, when the conductivity of air and surfaces increases.
One of the key reasons is the ageing of materials. Rubber braiding wires over time dries up, is covered with microcracks and loses its insulating properties. A similar situation occurs with candle ceramics: constant thermal loads (heating to 2000 ° C during combustion and cooling) create internal stresses. If you add to this mechanical impact with careless replacement or oil, the risk of destruction of the insulator increases dramatically. A critical factor is also the gap between the electrodes.: if it is enlarged due to burnout, the resistance of the spark gap increases, and the voltage is easier to penetrate the insulation than to slip between the electrodes.
The impact of the environment cannot be underestimated. Water, snow or condensate, hit on the heated engine, instantly evaporate, but until that moment create a conductive film. If candle wells are not sealed or the rubber wire tips are damaged, moisture becomes an ideal conductor for leakage current. Oil that enters the wells due to wear of the valve cover or the glands of candle wells creates an even more dangerous situation, since the oil film conducts current at high voltages is better than pure water.
Symptoms of a faulty ignition system
Diagnostics of breakdown begins with the analysis of the behavior of the car. The first and most obvious sign is the unstable operation of the engine at idling. The motor can twitch, stall when gas is discharged or work with increased vibration. This is because the fuel in the cylinder with a pierced candle does not burn or does not burn completely, disrupting the balance of the entire unit. The electronic control unit (ECU) fixes the ignition gaps and tries to compensate for them by changing the composition of the mixture, but this is impossible with a physical breakdown.
The vehicle’s dynamic performance is also falling significantly. When accelerating, a “failure” is felt, the car does not pull, especially at high speeds or when climbing uphill. Fuel consumption can increase by 15-20%, as unburned gasoline is simply thrown into the exhaust system. In some cases, the driver may notice black smoke from the exhaust pipe and hear claps in the muffler, indicating that the fuel is burning in the exhaust tract.
Modern cars immediately signal the problem of the indicator sunbathing Check Engine on the dashboard. When connecting the diagnostic scanner, errors can be seen indicating ignition gaps in specific cylinders (e.g., P0301, P0302). However, drivers often hear a characteristic clicking sound, the intensity of which varies with engine speed.
Methods of visual and instrumental diagnostics
A comprehensive check is required to determine the exact breakdown site. Start with a visual inspection when the engine is turned off. Remove the decorative casing and carefully inspect the high-voltage wires and tips. Look for breakage marks in the form of dark stripes, dots or charring on the insulation. Any mechanical damage, cracks or melting indicates that the element needs immediate replacement. Pay special attention to the places of contact of the wire with the metal parts of the engine.
If there are no visual defects, the method of “blackout” is used. At dusk or in the garage, start the engine and open the hood. Carefully, using an isolated tool, inspect the area around the candles. Bright blue sparks will indicate the exact location of the current leak. Be very careful: the voltage is very high, and although the current is small, the impact can be noticeable, and the risk of getting burned from hot engine parts is great. You can also use a special spray to search for leaks, which, when hitting the breakdown site, changes color or begins to spark more intensely.
Instrumental diagnostics includes checking the resistance of high-voltage wires with a multimeter. Normal values are usually in the range of 3 to 10 kOhms (depending on the length of the wire and the type of system). If the resistance is infinitely large (break) or close to zero (short circuit), the wire is faulty. Also checked the condition of candles: the soda, oily plaque or destroyed insulator indicate the need to replace them. It is important to check not only the candle itself, but also the condition of the candle well for the presence of oil or moisture.
☑️ Diagnosis of candle breakdown
The effect of oil and moisture on the work of candles
The oil in the candle wells is one of the most common causes of breakdown. The oil can get there through worn-out pads of the valve cover or special glands of candle wells (if they are structurally provided). While in the well, the oil covers the ceramic insulator of the candle and the inner surface of the tip of the high-voltage wire. At high voltages, the oil film becomes conductive, creating a path for current directly to the engine body. As a result, the spark on the electrodes of the candle either disappears completely or becomes very weak.
Removing this problem requires not just replacement of candles, but engine repair. It is necessary to remove the valve cover, replace the gasket and oil glands, and also carefully clean the wells from the remnants of oil. If you just wipe the oil and put new candles, after a while the situation will repeat. In addition, oil can corrode the rubber wire tips, making them porous and conductive, which will require replacing the entire set of wires or coils.
Moisture acts in a similar way, but is seasonal. After washing the engine, driving through deep puddles or in heavy fog, water can condense in candle wells. Unlike oil, water can evaporate when the engine is heated, so sometimes the problem goes away after a long trip. However, constant humidity accelerates the corrosion of the contacts and can lead to irreversible damage to the insulation. To protect against moisture, it is recommended to use special water-repellent sprays for high-voltage systems.
⚠️ Warning: Attempting to wash candle wells with water without further thorough drying with compressed air is guaranteed to lead to a breakdown. Water combined with high voltage will create ideal conditions for short circuit.
Table: Normal parameters and signs of malfunction
For the correct assessment of the state of the elements of the ignition system, it is necessary to know their normative indicators. Below is a table that helps to distinguish a serviceable part from a replacement. Remember that the parameters may vary slightly depending on the vehicle manufacturer and engine type.
| Parameter | Normal value. | Sign of malfunction | Consequences of neglect |
|---|---|---|---|
| Candle gap (gasoline) | 0.7. 1.1 mm | Clearance > 1.3 mm or < 0.6 mm | Insulator failure or ignition failure |
| Resistance to BB wire | 3 - 10 kom | Infinity or value leaps | Unstable spark, three-engine |
| Color of the insulator | Light brown | Black gar, oily, red plaque | Kalyl ignition, mass breakdown |
| Clearance between electrodes | uniform throughout the circumference | Electrode melting, erosion | Increased breakdown voltage, load on the coil |
How to clean candles properly?
If light stain appeared on the candles, they can be gently cleaned with a soft brush and a special cleaner. However, if the gap is broken or there is damage to the ceramics, cleaning won’t help – just replacement. Do not use sandpaper, it leaves conductive particles.
Consequences of operation of the car with broken candles
Long driving with a faulty