Note: If the original spark plugs are to be reinstalled on the engine after checking their condition, they must be screwed strictly into the previous cylinders – mark them accordingly.
Tools needed when replacing spark plugs
- 1. Spark plug head - Equipped with a special soft insert, eliminating the possibility of accidental damage to the porcelain insulator when unscrewing the spark plug.
- 2. Torque wrench - Although not mandatory, it provides a reliable guarantee that the spark plugs are tightened correctly.
- 3. Ratchet drive - Used in combination with a spark plug head and torque wrench.
- 4. Extension cord - Depending on the model and its auxiliary units, access to the spark plugs may be limited to varying degrees, so using extensions of the appropriate shape and design will significantly facilitate the procedure.
- 5. Tool for measuring and adjusting spark plug gaps - There are several types of this type of tool available - make sure that the tool comes with a feeler gauge that matches the size of the spark plug gaps in your vehicle.
In most cases, replacing spark plugs requires a special spark plug head (with soft liner inside) complete with ratchet drive, as well as a set of wrench drive extensions and a tool for checking and adjusting interelectrode gaps (see illustration above). A special tool is also available to safely disconnect the high-voltage wire ends from the spark plug tails, although its use is not strictly required. Using a torque wrench will help achieve the correct tightening force for the spark plugs.
The best thing to do is to keep a set of replacement spark plugs in your car at all times, with the interelectrode gap adjusted correctly. When buying new spark plugs, make sure that they meet the parameters of your car's engine. The necessary information is provided in Specifications to this Chapter and also on the VECI label attached under the hood (in case of discrepancies, preference should be given to the requirements of the latter).
1. Start removing the spark plugs only after the engine has completely cooled down. In order not to waste time, use the pause to check the condition of the replacement set. Carefully inspect the new spark plugs; if the slightest cracks are found in the insulator, the corresponding spark plug should be rejected. Measure the size of the interelectrode gaps of the new set (see below).
2a. The spark plug gap is checked by inserting the appropriate feeler gauge into the gap and must comply with the requirements given on the VECI label (see also Specifications to the Chapter Engine electrical equipment). The required thickness of the probe should slide with slight resistance between the side and central electrodes of the spark plug (refer to the accompanying illustration).
2b. The gap can be adjusted using a special device, usually included in the measuring device; bend the side electrode of the spark plug accordingly (refer to the accompanying illustration).
3. If the side electrode is not positioned exactly above the central one, adjust its position accordingly. Make sure there are no cracks or other damage in the porcelain insulator of the spark plug. The presence of any kind of defects in the insulator is unacceptable.
Removal
1. To avoid disruption of the ignition order when connecting the coils, service each spark plug individually. Disconnect the coil from the spark plug of the first cylinder, do not pull the wire under any circumstances!
Note: On 2UZ-FE engine models with ignition coils located above the spark plugs, the entire assembly must be removed from the cylinder head cover to gain access to the spark plugs (see chapter Engine electrical equipment).
2. If you have a source of compressed air on hand, use it to remove debris from the spark plug niches of the engine (a regular bicycle pump would be just as good for this purpose).
Caution! When using compressed air, do not forget to wear safety glasses!
3. Remove the spark plug.
4. Compare the removed spark plug with the identification card below, which will allow you to qualitatively assess the overall condition of the engine.
Installation
1a. Before screwing in new spark plugs, lightly lubricate their threads with anti-seize sealant (refer to the accompanying illustration). Thread one of the new spark plugs into the appropriate hole in the engine by hand. After making sure the spark plug is not cross-threaded, tighten it to the specified torque (if you have a torque wrench at hand).
1b. To make the spark plug installation easier, pull a piece of flexible fuel hose over its tail (refer to the accompanying illustration). This eliminates the possibility of thread stripping, since the slightest biting will simply cause the hose to start turning.
2. Using a rotary and translational motion, place the coil on the spark plug tail.
3. Repeat the procedure for the remaining spark plugs.
Spark Plug Condition Chart
Normal condition of the candle
Symptoms: Grey-brown color and slight wear of the electrodes. The glow number of the spark plugs corresponds to the type of engine and its general condition.
Recommendations: When replacing spark plugs, install spark plugs of the same type.
Wear
Symptoms: Rounding of the electrodes with a small accumulation of deposits at the working end. Color is normal. Causes difficulty starting the engine in cold, wet weather and increased fuel consumption.
Recommendations: Replace the spark plugs with new ones of the same type.
Coal deposits
Symptoms: The presence of soot indicates an over-rich fuel-air mixture or weak spark intensity. Causes misfires, difficult starting and leads to unstable engine operation.
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 spark plugs with a longer insulator, which increases resistance to contamination.
Ash formation
Symptoms: Soft, brownish deposits on one or both spark plug electrodes. These are caused by oil and/or fuel additives. Excessive buildup can insulate the electrodes and cause misfires and rough running under acceleration.
Recommendations: If deposits accumulate quickly, replace the oil seals, which will prevent oil from entering the combustion chambers. Try changing the fuel brand.
Oiling
Symptoms: Oiling of the spark plug is caused by worn out oil deflector caps. Oil gets into the combustion chamber through worn valve guides or piston rings. Causes misfires, difficult starting and leads to unstable engine operation.
Recommendations: Perform mechanical repairs and replace spark plugs.
Short circuit of electrodes
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Symptoms: Combustion waste gets into the interelectrode space. Solid deposits accumulate, forming a bridge between the electrodes. Leads to ignition failure in the cylinder.
Recommendations: Remove deposits from the interelectrode space.
Overheat
Symptoms: Porous, white insulator, erosion of electrodes and absence of any deposits. Leads to a reduction in spark plug life.
Recommendations: Check if it meets the requirements Specifications the glow plug rating, whether the ignition timing is set correctly, whether the fuel-air mixture is too lean, whether there are any vacuum leaks in the intake manifold and whether the valves are jammed. Also check the coolant level and whether the radiator is clogged.
Too early ignition
Symptoms: The electrodes are melted. The insulator is white, but may also be contaminated due to misfiring or foreign particles entering the combustion chambers. May cause engine failure.
Recommendations: Check the glow number of the installed spark plugs, the ignition timing, and the quality of the mixture (isn't it too poor?), whether the cooling system is clogged and whether the lubrication system is functioning normally.
Conductive gloss
Symptoms: The insulator has a yellowish color and a polished appearance. Indicates a sudden increase in temperature in the combustion chambers during sharp acceleration. Normal deposits melt, acquiring the appearance of a varnish coating. Leads to misfires at high speeds.
Recommendations: Change the spark plugs (cooler, while maintaining the same driving style).
Detonation
Symptoms: Insulators may be chipped or cracked. Insulator damage may also result from improper spark plug gap adjustment. Piston damage may result.
Mechanical damage
Symptoms: Can be caused by foreign material entering the combustion chamber or by the piston hitting a spark plug that is too long. Leads to cylinder failure and piston damage.
Recommendations: Remove foreign particles from the engine and/or replace. Since the service life of spark plugs is usually 15,000 km, it is sufficient to clean them every 8,000 km.
Splashing
Symptoms: After a long period of misfire, deposits may become loose while the combustion chamber remains at operating temperature. At high speeds, deposits flake off the piston and stick to the hot insulator, causing misfires.
Recommendations: Replace the spark plugs or clean and reinstall the old ones.