Warning! In the electronic ignition system, a very high voltage is generated! Be careful, observe all necessary precautions when servicing any system components, including not only the main (ignition coil ignition module), but also related, such as spark plug connectors tachometer and other equipment!
Attention! All spark plug replacement work should only be done on a cold engine (engine temperature can be touched by hand) otherwise, when removing the spark plugs on a hot engine, you can damage the internal thread of the spark plug hole on the cylinder head.
1. The correct functioning of the spark plugs is largely determined by the efficiency of the engine output. It is important that the spark plugs of the exact type specified by the manufacturer are installed on the engine). Attempts «improve» engine by installing more expensive and at first glance the best candles are likely to lead to the opposite result. On a serviceable engine, the need for unscheduled maintenance of spark plugs is extremely rare; you should not unscrew the spark plugs unnecessarily to check. To avoid accidental damage to the electrodes, do not service or clean the spark plugs without the use of special equipment.
2. To replace spark plugs, a special spark plug head is required (16 mm) complete with extension, universal joint, torque wrench (see resist. illustration). Using a torque wrench will allow you to achieve the correct tightening torque for the candles.
Attention! Use a spark plug wrench with an elastic insert to prevent damage to the spark plug insulator!
22.2 Tools required when changing spark plugs:
1. Candle head - Equipped with a special elastic insert, which excludes the possibility of accidental damage to the porcelain insulator when the candle is turned out.
2. Torque wrench - Not a required tool, it provides a reliable guarantee of the correct tightening torque of the spark plugs.
3. Ratchet drive - It is used in a set with a candle head and a torque wrench.
4. Extension - Depending on the model and its accessories, access to the spark plugs can be limited to varying degrees, so the use of extensions of the appropriate shape and design will greatly facilitate the procedure.
5. Spark Plug Gap Tool There are several types of this kind of tool available, make sure the tool is equipped with a feeler gauge that matches your vehicle's spark plug gap size.
3. To free access to the spark plugs, you must first remove the ignition module / coils (see chapter 5).
4. On DOHC engines spark plugs are deeply recessed into the candle niches, so you will need a key drive extension to turn them out (see resist. illustration). Putting the head on the candle, connect the drive and, gently turning the collar counterclockwise, unscrew the candle.
5. Compare the removed spark plug to the condition map shown in the photographic insert to give a good idea of the overall condition of the engine.
22.4 Removing a spark plug from a deep niche using a special key: 1. Crank with ratchet drive; 2. Extension; 3. Cardan joint; 4. Candle head (with elastic insert); 5. Spark plug
6. Checking the condition of the spark plugs gives a good idea of the condition of the engine. If there are no traces of any deposits on the insulator of the central electrode, this indicates a re-leaning of the air-fuel mixture, or that it is being used excessively «hot» candle (heat dissipation from the insulator to the housing «hot» candlelight is much less intense than on «cold»)
7. The presence of black deposits on the electrodes indicates a re-enrichment of the mixture, and if the deposits still have an oily consistency, you should also consider a more detailed assessment of the degree of wear of the internal components of the engine.
8. A coating of a golden or gray-brown hue on the insulator confirms the good condition of the engine and the correct layout of the air-fuel mixture.
9. Modern engines use different types of spark plugs. Multi-electrode spark plugs are widely used (see resist. illustration), which have increased wear resistance and reliability. The installation of interelectrode gaps on such candles is made at the factory and, as a rule, does not need any adjustments. If necessary, the installation of interelectrode gaps should be carried out in accordance with the instructions of the candle manufacturers.
22.9 Most modern models come standard with multi-electrode spark plugs
10. Measurement of the interelectrode gap is carried out using a special wire-type probe (see resist. illustration 22.10a). When adjusting, only the side electrodes should be bent - attempts to deform the central electrode are fraught with irreversible damage to the insulator. If a blade-type feeler gauge is used to measure the spark plug gap, the gap can be considered correctly adjusted when the feeler blade is passed into it with slight resistance (see resist. illustration 22.10b)
22.10a Checking the size of the interelectrode gap using a wire-type meter
22.10b Checking the electrode gap with a blade-type feeler gauge
11. Before installing the candle, make sure that the threads on the body and the outer surface of the candle are well cleaned.
12. If, during inspection of the candle, damage to the threaded connection is found, the candle must be replaced, and if the thread in the head of the block is damaged, it is necessary to cut a new thread with a special tool without removing the head for a special adapter, which is screwed onto a standard candle. Suitable tools and various repair kits are commercially available for this purpose (e.g. BERU).
13. Thread one of the new spark plugs into the appropriate hole in the engine by hand. After making sure that the candle is not skewed in the thread, tighten it with the required force. To facilitate the procedure for baiting a candle, pull a piece of flexible fuel hose onto its shank (see resist. illustration) in order to exclude the possibility of thread breakage, since at the slightest biting, the hose will simply begin to turn. Proceeding in a similar manner, install all the remaining candles.
22.13 To avoid damage to the threads in the cylinder head as a result of misalignment of the spark plugs, they should be baited using a piece of fuel hose that is put on the shank
14. Replace all removed components.
Spark Plug Diagnostics
Coal deposits
Symptoms: The presence of soot indicates an over-rich air/fuel mixture or a weak spark. Causes misfiring, difficult starting and engine instability.
Recommendations: Check if the air cleaner is clogged, if the fuel level in the float chamber is too high, if the air damper is stuck, and if the contacts are too worn. Try using plugs with a longer insulator, which increases fouling resistance.
Oiling
Symptoms: Lubrication of the spark plug is caused by wear on the valve stem seals. Oil enters the combustion chamber through worn valve guides or piston rings. Causes misfiring, difficult starting and engine instability.
Recommendations: Carry out mechanical restoration work and replace the spark plugs.
Overheat
Symptoms: Porous, white insulator, electrode erosion and absence of any deposits. This will shorten the life of the spark plug.
Recommendations: Check if the glow rating of the installed plugs meets the requirements of the Specifications, if the ignition timing is set correctly, if the air-fuel mixture is supplied too lean, if there are vacuum leaks in the intake pipeline and if the valves are stuck. Also check the coolant level and check if the radiator is clogged.
Too early ignition
Symptoms: The electrodes are melted. The insulator is white, but may be dirty due to misfiring or foreign particles entering the combustion chambers. May lead to engine failure.
Recommendations: Check the glow number of the installed candles, the ignition timing, the quality of the mixture (isn't it too poor), whether the cooling system is clogged and the lubrication system is functioning properly.
Electrically conductive gloss
Symptoms: The insulator has a yellowish color and a polished appearance. It speaks of a sudden increase in temperature in the combustion chambers during sharp acceleration. At the same time, ordinary deposits are melted, acquiring the appearance of a varnish coating. Causes misfiring at high speeds.
Recommendations: Change spark plugs (colder, while maintaining driving style).
Closing the electrodes
Symptoms: Waste products of combustion enter the interelectrode space. Solid deposits accumulate, forming a jumper between the electrodes. Leads to ignition failure in the cylinder.
Recommendations: Remove deposits from the interelectrode space.
The normal state of the candle
Symptoms: Grey-brown flowers and slight electrode wear. The number of glow plugs corresponds to the type of engine and its general condition.
Recommendations: When replacing spark plugs, use spark plugs of the same type.
Ash formation
Symptoms: Soft brownish deposits on one or both spark plug electrodes. The source of formation is the additives used in the oil and/or fuel. Excessive buildup can insulate the electrodes and cause misfiring and engine instability when accelerating.
Recommendations: If deposits build up quickly, change the oil seals to prevent oil from entering the combustion chambers. Try changing the brand of fuel.
Wear
Symptoms: Rounding of the electrodes with a slight accumulation of deposits at the working end. The color is normal. Causes engine start difficulty in cold, wet weather and increased fuel consumption.
Recommendations: Replace the spark plugs with new ones of the same type.
Detonation
Symptoms: Insulators may be chipped or cracked. Insulator damage can also result from inaccurate spark plug gap adjustment. May damage pistons.
Splashing
Symptoms: After misfiring for a long period of time, deposits can loosen while maintaining the operating temperature in the combustion chamber. At high speeds, deposits flake off the piston and adhere to the hot insulator, causing misfiring
Recommendations: Replace spark plugs or clean and reinstall old ones.
Mechanical damage
Symptoms: May be caused by foreign material entering the combustion chamber or by the piston hitting a spark plug that is too long. Lead to cylinder failure and piston damage.
Recommendations: Remove foreign particles from the engine and/or replace the spark plugs.
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