If unscheduled replacement of spark plugs is necessary, only spark plugs recommended for this engine should be used.
This will prevent engine failures, a decrease in its power, a deterioration in throttle response, an increase in the content of harmful substances in the exhaust gases and interference with radio reception. Particularly important characteristics of candles are the number of electrodes, glow number and, in some cases, the ability not to interfere with radio reception.
Normal operation of spark plugs is one of the most important conditions for the efficient operation of the engine. Only spark plugs recommended by the manufacturer should be installed on the engine. With a good engine, spark plugs are rarely cleaned.
V6 petrol engines
Loosen the clamps and remove the air pipe connecting the air filter and the throttle body.
Pic. 3.1–41. Location of engine cover screws
Loosen the four screws and remove the engine cover (pic. 3.1–41).
Pic. 2–10. The location of the high-voltage wires on the spark plugs of a V6 gasoline engine
Remove the high voltage wires from the spark plugs (pic. 2–10).
Clean the spark plugs with a brush, vacuum cleaner or compressed air to prevent dirt from entering the engine cylinders after the spark plugs are removed. Unscrew the spark plugs with spark plug wrench 3122 B.
Screw in new spark plugs and tighten them to 30 Nm.
Connect high voltage wires to spark plugs.
Install the engine cover and air pipe connecting the air filter and throttle body.
V8-2V petrol engines
Loosen the clamps and remove the air pipe connecting the air filter and the throttle body.
Pic. 3.2–3. Location of engine cover screws
Loosen the screws and remove the engine cover (see fig. 3.2–3).
Release the clips and disconnect the electrical connectors from the ignition coils.
Pic. 2–11. The location of the ignition coils on the spark plugs of a V8-2V gasoline engine
Unscrew the ignition coil bolts and remove them (pic. 2–11).
Clean the spark plugs with a brush, vacuum cleaner or compressed air to prevent dirt from entering the engine cylinders after the spark plugs are removed. Unscrew the spark plugs with spark plug wrench 3122 B.
Screw in new spark plugs and tighten them to 30 Nm.
Check and, if necessary, replace the sealing rings, install the ignition coils and secure them with bolts, tightening them with a torque of 10 Nm.
Connect the electrical connectors to the ignition coils.
V8-5V petrol engines
Unscrew the screws and remove the engine cover (see fig. 3.2–3).
Left cylinder head
Pic. 2–12. Location of electrical connectors (1) and bolts (3) fastening ignition coils, as well as bolts (2) mounting bracket on the left cylinder head of a V8–5V gasoline engine
Disconnect electrical connectors 1 (pic. 2–12) from ignition coils.
Unscrew bolts 2 and remove the bracket.
Unscrew bolts 3 fastening coils of ignition and remove coils.
Clean the spark plugs with a brush, vacuum cleaner or compressed air to prevent dirt from entering the engine cylinders after the spark plugs are removed. Unscrew the spark plugs with spark plug wrench 3122 B.
Screw in new spark plugs and tighten them to 30 Nm.
Check and, if necessary, replace the sealing rings, install the ignition coils and secure them with bolts, tightening them with a torque of 10 Nm.
Install the bracket and connect the electrical connectors to the ignition coils.
Right cylinder head
Pic. 2–13. Location of electrical connectors (1) and bolts (3) fastening ignition coils, as well as bolts (2) mounting bracket on the right cylinder head of a V8–5V gasoline engine
Disconnect electrical connectors 1 from ignition coils (pic. 2–13).
Unscrew bolts 2 and remove the bracket.
Unscrew bolts 3 fastening coils of ignition and remove coils.
Clean the spark plugs with a brush, vacuum cleaner or compressed air to prevent dirt from entering the engine cylinders after the spark plugs are removed. Unscrew the spark plugs with spark plug wrench 3122 B.
Screw in new spark plugs and tighten them to 30 Nm.
Check and, if necessary, replace the sealing rings, install the ignition coils and secure them with bolts, tightening them with a torque of 10 Nm.
Install the bracket and connect the electrical connectors to the ignition coils.
Checking spark plugs
By the appearance of the spark plugs, you can diagnose the condition of the engine. A clean, white, non-tarnished spark plug insulator indicates a too lean air-fuel mixture. It also indicates that the candle is too hot (heat is removed from the central electrode slowly). It is necessary to adjust the composition of the air-fuel mixture or replace the spark plug.
The deposition of dry soot indicates a too rich mixture. If the coating is black, oily - the engine is worn out, it must be checked and repaired. If the insulator is covered with a light brown coating, then the mixture is optimal and the engine is in good condition.
Too large or too small an electrode gap, which changes the size of the spark, leads to a decrease in engine efficiency. The gap must always meet specifications and is checked with a wire gauge or feeler gauge. You can correct the gap by bending the side electrode with a special tool. In no case should the central electrode be bent, as this can lead to breakage of the insulator and failure of the candle.
Before installing the spark plug in the engine, check that the threads are clean and undamaged.
There are two types of seals installed in the cylinder head: flat seated and resilient (steel or copper-asbestos) with a gasket or with a conical seat without a gasket. When installing a new candle, first of all, it is necessary to check which seal is provided in the cylinder head, the diameter and length of the threaded part. If you install a candle with a long threaded part in a head with a short thread, then the protruding part of the candle will be covered with carbon deposits and resins, lead deposits. The candle will overheat, possibly melting the threads. When turning out such a candle, the threads in the cylinder head can be damaged. With a short threaded part of the candle and a long one in the head, soot and various deposits clog the thread, it melts. After long work, you have to go through the threaded part in the cylinder head with a tap, but so that the dirt does not remain in the cylinder.
The most important parameter characterizing the candle is the temperature regime of its elements and, first of all, the central electrode and the surface of the insulator skirt. The main problem in creating a spark plug for a high-speed engine is the fulfillment of conflicting requirements. On the one hand, it is necessary to ensure a sufficiently high temperature of the insulator skirt to prevent the formation of soot on it, leading to shunting, during long-term operation at low loads and idling, especially at low temperatures. When switching to high loads at high temperatures, the spark plug insulator self-cleansing due to the burnout of deposits on it. On the other hand, at high speed and high load, the temperature of the central electrode and the lower part of the insulator should not exceed the upper limit at which glow ignition occurs (ignition of the mixture even before a spark from the ignition system occurs). From cycle to cycle, ignition occurs earlier and earlier, the temperature of the parts rises until something burns out: at best a candle, at worst a piston. So, because of a small candle, there can be big trouble.
How to prevent the possibility of the occurrence of incandescent ignition? First of all, you need to follow the correct (according to instructions) setting the ignition timing, preventing too early ignition.
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