Reading spark plugs means examining and evaluating their condition and tip color. Learn to do this to understand the quality of vehicle operation, foresee potential problems and intervene promptly; in this way, you can also recognize when it is necessary to change them to improve engine performance.
Steps
Part 1 of 3: Identifying the Signs of a Damaged Candle
Step 1. Observe the light gray or metallic brown color of a spark plug in good condition
An undamaged item is typically light gray or just brown in color. There should be no encrustations on the surface; if you bought new candles, they should all be similar in color.
- A "good" spark plug does not need to be replaced.
- If one of the cylinders sticks even though the spark plug is in good condition, the problem could be the cable; try to change it to see if this intervention solves the problem.
Step 2. Look for soot
It generally tends to accumulate when the engine receives a mixture that is too greasy, that is, too rich in fuel in proportion to the air at the moment of detonation. Look for black soot on the surface of the candle.
- The presence of a black, dry substance indicates a fatty mixture.
- It may be sufficient to clean the spark plug and thus avoid replacing it; just wipe it with a rag or spray it with brake cleaner.
- If the engine gets too rich a fuel mixture, you need to take the car to the mechanic to figure out why.
Step 3. Check if the oil-soiled spark plug is wet
If there is an oil leak in the engine seeping through the worn piston seals or through the valves on the cylinder head, the spark plugs may be dirty. Check for fresh oil on the spark plug itself.
- Oil-stained candles are usually damp, while soot-covered ones are dry.
- You have to locate and fix the leak to prevent the candles from getting greasy.
- An oil leak can cause serious damage to the engine; take the car to the mechanic for a diagnosis and repair.
Step 4. Watch out for burns and blisters
If you have problems with overheating, the candles could burn out. Look for any swelling or heat damage on the tip insulation, such as molten plastic or burnt metal.
- If a candle is damaged by heat, you need to change it.
- Overheating problems can be caused by a lack or scarcity of coolant.
- Add liquid to the radiator if the level is insufficient; otherwise, it may need to be washed.
Step 5. Check for severe wear
In practice, candles have been "exploited" for too long; if those present on old vehicles have never been replaced, they could stop working, even if they do not show any symptoms of those described above.
- In the presence of considerable wear, the spark plug could also break when you try to remove it; you may also notice the erosion of the connections and fractures in the plastic.
- In this case you have to replace the piece.
Part 2 of 3: Remove the Candles
Step 1. Disconnect the battery
Before working on the vehicle's electrical system, it is always important to disconnect the power supply. Use a correctly sized wrench or socket to loosen the nut securing the black lead to the negative battery terminal; then fit the cable laterally to it.
It is not necessary to disconnect the positive lead
Step 2. Remove the spark plug
The spark plug cables come from the ignition source, which can be the ignition coil or the distributor, and connect to the spark plugs themselves through holes in the engine head. Grab the wire at the base, near the spark plug, and pull it to detach it.
- Generally, you can hear a "pop" and need to exert a good amount of force.
- Do not pull the wire by itself, as you may tear it, leaving the base connected to the spark plug.
Step 3. Clean the area around the hole in the cylinder head
Make sure there is no residue, oil or dust before unscrewing the spark plug; this is fixed directly into the cylinder chamber and anything that falls into it will enter the engine.
- The residues that fall into the combustion chamber cause serious damage to the engine the next time it is turned on.
- If you notice a foreign body entering the spark plug hole, use a wet vacuum or can of compressed air to extract it before reinstalling the spark plug.
Step 4. Use the appropriate socket wrench to unscrew the element
This compass resembles the traditional ones, but it is equipped with an internal rubber cap that holds the spark plug after unscrewing it; a normal bush of the correct size simply loosens and unscrews the piece without removing it from the hole.
Spark plugs are typically available in a single diameter and the socket wrench will almost always fit every model
Step 5. Pull out the spark plug with the socket wrench
Unscrew it by turning it counterclockwise until it is completely free from the thread; then slide the key out gently while the candle is inside.
If the spark plug is still hot, you must leave it in the socket while you inspect it
Part 3 of 3: Install the New Spark Plugs
Step 1. Purchase the correct replacement
Ask the shop assistant for help in choosing the right model for your engine; spark plugs burn at different temperatures, so it is important to buy those that fit your vehicle.
- You can understand which model to choose by consulting the use and maintenance manual of your car (check the model and year of production of the vehicle to which it refers).
- Before proceeding, make sure you have disconnected the battery.
Step 2. Use compressed air to clean the hole
Before installing the replacement, use a can of compressed air or a real compressor to get rid of any dust or debris that may have fallen into the spark plug housing; by doing so, you prevent a foreign body from reaching and damaging the engine.
- Be very careful to prevent any debris or small tools from falling into the hole.
- A wet vacuum is often the best solution for extracting something that has already fallen into the housing.
Step 3. Make sure the new candle has the right gap
The gap between the electrodes defines the length of the spark that serves to trigger the detonation of the fuel and air mixture inside the engine. Use the gap tool to adjust the gap before inserting the replacement spark plug.
- Most of these adjustment tools have the shape of a variable thickness disc; insert the edge between the electrodes and turn it until the distance between them is the right one for your vehicle model.
- Find the appropriate gap value for the motor size by consulting the user and maintenance manual.
Step 4. Insert the candle into the compass
Insert it into the rubber cap located in the tool and then insert the latter on the extension of the key which must be at least a few centimeters long; in this way, you can screw the candle as if it were a simple bolt.
- Make sure the extension is long enough for you to properly snap the replacement into place.
- Most of these sleeves are 9mm in diameter, so make sure the extension is the same size.
Step 5. Screw in the candle by hand
Rotate the extension clockwise without exerting too much downward pressure, otherwise you may prevent the thread from aligning properly, causing damage that requires expensive repairs.
- Rotate the extension clockwise until the spark plug is fully engaged with the engine.
- If you suddenly encounter strong resistance which then dissipates, unscrew the spark plug and start over to avoid crossing the thread.
Step 6. Tighten the spark plug with the socket wrench
Once screwed into the motor by hand, connect the handle to the extension and lightly tighten the piece to make sure that the vibrations do not loosen it; it is not necessary to apply too much force to ensure proper tightening.
- Do not over tighten the candle as you may break it or have difficulty removing it in the future.
- If you break the part, you have to rely on a mechanic to get it out.
Step 7. Plug the cable back in
Take the one you detached earlier and snap it firmly onto the end of the new candle; you should hear a snap when the connection is securely restored.
- You may decide to apply some dielectric grease to the spark plug or wire to ensure good electrical contact.
- When finished, connect the battery again.
