The most typical causes of spark plug failure are carbon deposits from incomplete fuel combustion products, or an increase in the spark gap, which happens from electrode wear. But do not rush to tidy up the candles.
The reason for the formation of gaps lies in the technical condition of the engine, which does not provide correct adjustment of the fuel-air mixture, as a result of which an excessively rich working mixture is formed. The reasons may also be a dirty air filter, a malfunction of the cold starting system, etc.
Check the spark plugs directly on a running engine using a neon lamp or the shutdown method. Option of checking on a special device is possible. With the help of a neon lamp, it is possible to establish the presence of high voltage at the electrodes of the spark plug during the operation of the ignition system. To do this, connect one wire of the lamp to the engine ground, and the other, alternately to the central electrodes of the candles. In this case, the engine should be well warmed up and run at low revs. With a working candle, the lamp emits a bright, intermittently flashing light. Conversely, a weak glow is a consequence of insufficient voltage.
To determine the exact cause of the malfunction, swap the serviceable and defective spark plugs from another cylinder of the same engine. In the event of engine interruptions, check all candles on a special device in the chamber, where compressed air is pumped under a pressure of 7-8 kg / cm2. If there is no spark during the check, interruptions in sparking occur, or a spark jumps over the surface of the insulator skirt, then the candles are faulty.
There is a special round dipstick to check the gap. If necessary, adjust the gap by bending the side electrodes using a strip with a side slot. For all candles on a given engine, the gaps between the electrodes must be the same. Dry or oily dark carbon deposits are removed from the candles in a sandblasting unit with quartz sand with a grain size of 1000-2500 holes / cm2.