MOT No. 36
The maintenance plan calls for the replacement of spark plugs every 30,000 km. This interval seems real to us and it is not worth extending it. It is necessary to carefully monitor the health of the ignition system, especially on vehicles equipped with a catalytic converter.
Removing spark plugs
Unscrew the spark plugs and put them in according to the sequence of cylinders, so that from the condition of the spark plug it is possible to draw conclusions about the condition of the corresponding cylinder.
If the spark plugs are difficult to turn out, do not use force or the threads in the light alloy head may break.
Warm up the engine and now remove the spark plugs.
When installing, do not screw cold candles into a hot engine, then it will be difficult to turn them out.
Spark plugs must be tightened to 20 Nm. If you don't have a torque wrench handy:
Screw in the spark plug until the sealing ring is in contact - in this case it can no longer be turned either by hand or with a spark plug wrench without the use of force.
Now, if you installed new spark plugs, tighten with a spark plug wrench about a quarter of a turn.
If you are using used spark plugs, it will be sufficient if you turn the spark plug wrench about 15°.
Spark plugs must be tightened to 20 Nm. If you do not have a torque wrench at hand: screw in the spark plug until the sealing ring is in contact (arrow), when it can no longer be turned by hand or with a candle wrench without the use of force. Now, if you installed new spark plugs, tighten with a spark plug wrench about a quarter of a turn. If you are using candles that have already been used, it will be sufficient if you turn the candle wrench another 15°.
Nagar on candles
Spark plugs, in a certain sense of the word, are witnesses of combustion in the engine. Appearance of spark plugs (soot) allows you to determine whether the engine is operating optimally.
Beforehand, thoroughly warm up the engine on a country road or motorway. Control after a short distance may lead to incorrect conclusions. Look at the tip of the insulator cone with the middle electrode and side electrodes.
The tip of the insulator cone is gray or brownish: a well-adjusted injection system, the engine runs economically.
Strong deposits: Additives in engine oil or fuel or increased oil consumption may be the cause. Perhaps you should change the brand of oil or fuel.
Black soot-like deposits: spark plug does not reach the self-cleaning temperature due to frequent short trips, incorrect glow rating
The tip of the insulator cone is whitish: the ignition timing is too early The electronic ignition timing control or the knock sensor does not function.
Melting marks on the center and ground electrodes: glow ignition caused by deposits in the combustion chamber, overheated injectors, incorrect ignition timing, poor ignition timing, a faulty knock sensor, or engine overheating.
The insulator cone is broken, in the initial stage it is distinguishable as a thin crack: knocking combustion due to poor fuel, incorrectly adjusted ignition, knocked down ignition timing, faulty knock sensor, insufficient engine cooling or lean mixture due to unaccounted for air.
Oil layer on the electrodes and inside of the spark plug: damaged piston rings, valve guides or valve stem seals.
If there are no indicated signs on the candles, and the engine still starts slowly or works intermittently, the reason may still lie in the candles. Invisible cracks in the ceramic insulator can fill with condensing fuel during a cold start, causing the spark to leak. Candles may fail to work, although a spark is visible when the candles are removed.
Gap between electrodes
The mixture of fuel and air, as well as combustion products, are corrosive to the metal electrodes of spark plugs. And high voltage, when a spark jumps, tears out particles of metal, due to which the gap between the electrodes increases in operation. The following spark plug electrode gaps are acceptable:
- 4- and 5-cylinder engines: 0.7-0.9 mm:
- 6-cylinder engines: 0.9-1.1 mm.
The high-voltage wires of the ignition distributor are connected to the spark plugs according to the ignition order. The numbers show which cylinder (counting method: front to back) the appropriate wire must be connected. On the left is a 4-cylinder engine, on the right is a 5-cylinder.
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