How to check the spark plugs. How to find a faulty spark

Very often the cause of unstable work of the engine of the vehicle (especially on idle) and the fall of his power is the fault of the spark plug.

2015-11-19 04:59:50 353

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Very often the cause of unstable operation of the vehicle engine (especially at idle) and the fall of his power is the fault of the spark plug. When the engine is not developing the necessary capacity or, as they say, "troit", the first thing to do is, check for integrity of the spark plug and replace the faulty spare candle.

Search defective candles

On the engine is removed from the contact tip of a candle wire of a high voltage coming from the distributor. This manipulation is preferably carried out by wearing gloves or wrapping your hand with a dry cloth, because the breakdown current through the insulation is though not life threatening, but will still be quite noticeable and unpleasant invigorating. Removing the wire from the candle, listening to the rhythm of the engine. In case of a fall speed, change rhythm or stop the engine, put the wire back on the tip of the candle and move on to the next one. If its mode of operation has not changed, then the candle, which filmed the wire is broken.

Check spark at the breakdown

Check the spark breakdown is permissible only in older model vehicles, with contact system of ignition and a minimum of electronic equipment. Using this method of checking spark modern cars are stuffed with electronic brains that could lead to failure of onboard electronics. Unscrew the candle from the threaded connection of the cylinder head, at its conductive cap is put on the wire from the distributor, and the candle is pushed lateral to the vehicle. Turn on the ignition and "twist" the engine with the starter. A serviceable candle with clear periodicity is clearly seen the passage of a spark between the Central and side contact. This method is not perfect and not without error, as in unscrewed condition, at atmospheric pressure, the spark plug can generate a spark and in real conditions of compression when it is subjected to the pressure of the compressed gases in the combustion chamber, the discharge may not be. That is why to check the candles in the service centers use special stands with the pressure chambers and piezoelectric probes, pistols, simulating the working conditions of the spark with engine running. Probe for inspection of candles can be purchased at auto parts stores or make it yourself from a piezoelectric module with a lighter. The wire coming from the module, extendible and mounted to the tip unscrewed from the engine spark, and the piezoelectric unit is pressed against the housing of the plug and push the button on the unit. The presence of the electric discharge between the electrodes of the spark will indicate its serviceability, no – that candle was useless.

Signs of spark plug fouling

Do not rush to throw a broken spark plug, it is possible that it has lost its functionality due to burning of the electrodes, oiling, fouling or due to incorrect setting of the gap between the electrodes. In such cases, it is quite possible to "return to life", putting the gap by podpisania side of the electrode and remove the insulator and electrodes of accumulated soot and oil. Inspect the cone of an insulator of a candle. Normal insulator color will range from light gray to light brown. If it is too bright and white, then exhibited the ignition is too early, or the candle is too hot for this type of engine. The insulator should not contain scratches, cracks or chips, which can cause increased nagaroobrazovanie and output of a candle failure. And it should not be local areas of darker colour than the rest of the surface of the cone. Such candles it is better to replace with new ones.


Normal service life of the spark plug typically corresponds to 25-30 thousand kilometers of the car. The vehicles in severe conditions, the service life of spark plugs is reduced by half. For these vehicles, given the quality of petrol and oil at our gas stations combined with bad roads, can be attributed almost all cars do drive-bys domestic automobile spaces. It is therefore not surprising that after 15 or even 10 thousand kilometers candle will ask about a replacement.

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