Interpreting the condition of a spark plug consists of examining and evaluating the condition and color of the spark plug tip. You should learn to perform this procedure to understand how your vehicle works, anticipate potential problems, and fix them on time (as well as when to replace the spark plugs to get the best performance).
Steps
Part 1 of 3: Identify Signs of Spark Plug Damage
Step 1. Identify a light gray or brown metal on a good spark plug
A spark plug that is not damaged will appear light gray or possibly brown. In addition, it should not show any build-up on the shiny surface. If you bought new spark plugs, their colors should be pretty similar.
- It is not necessary to replace a good spark plug.
- If you have a faulty cylinder with a good spark plug, there is likely a problem with the wire. Try replacing it to see if the problem is resolved.
Step 2. Identify signs of char encrustation
Often times, these fouling occurs when the vehicle's engine runs too hard. This type of operation means that there is too much fuel in the fuel-air mixture when the spark plug is fired. Look for soot on the surface of the spark plug.
- Dry soot can form on the spark plug when the engine runs too hard.
- You can probably clean the soot from the spark plug and avoid the need to replace it. You can use a rag or apply brake cleaner to clean the spark plug.
- You will need to take the vehicle to a mechanic to diagnose why it is running too hard.
Step 3. Check the moisture on an oil-covered spark plug
If you detect engine oil leaking from worn piston rings or cylinder head valves, the spark plug may be covered in oil. Look for wet engine oil on the spark plug.
- Oil coated plugs will be wet, carbon coated ones will be dry.
- You need to address the oil leak to avoid fouling more spark plugs.
- An engine oil leak can cause major problems. Take your vehicle to a mechanic for diagnosis and repair.
Step 4. Look for bubbles or burns
If you're having overheating issues with your engine, a spark plug has likely burned out. Look for bubbles on the tip of the spark plug or signs of heat damage such as melted plastic or burned metal.
- You need to replace a heat-damaged spark plug.
- Overheating issues are likely due to worn or insufficient coolant levels.
- You should add coolant if the vehicle is low. If not, you may need to drain and rinse the radiator.
Step 5. Check for signs of severe wear
An excessively worn spark plug has simply been in use for a long period of time. Older vehicles that have never had their spark plugs replaced can experience failure without the spark plugs getting dirty in the manner mentioned above.
- Severe wear can cause a spark plug to come apart when removed. You can also detect signs of eroded connections or cracked plastic.
- You must replace excessively worn spark plugs.
Part 2 of 3: Remove the spark plugs
Step 1. Disconnect the battery
Before working on a vehicle's electrical system, it is important that you disconnect the battery. Use a suitable socket or hand wrench to loosen the nut that holds the ground wire to the negative battery terminal. Then slide the wire out of the terminal and tuck it aside.
You don't need to disconnect the positive cable
Step 2. Disconnect the spark plug wire
The spark plug wires come from an ignition source (such as coil packs or a distributor) and connect to the spark plugs through holes in the engine cylinder head. Hook the spark plug wire from the base and pull it back to disconnect it.
- Often times, the spark plug wires may require a bit of force to pull out.
- Avoid pulling on the wire itself, as you could break it and leave the base connected to the spark plug.
Step 3. Clean the area around the spark plug hole
Make sure the area around the spark plug holes is free of debris, dirt, or oil before removing the spark plugs. The spark plugs screw directly into the cylinder chamber, so anything that gets into the holes will fall directly into the engine.
- Debris falling into the holes can cause serious engine damage the next time you start it.
- If something falls into the holes, you should use an industrial vacuum or compressed air to remove it before reinstalling a spark plug.
Step 4. Use a spark plug wrench to unscrew the spark plug
This wrench looks like regular wrenches, but has a rubber cup inside that engages the spark plug as you unscrew it. An ordinary wrench of the correct size will simply unscrew the spark plug, but leave it in the hole.
Spark plugs generally come in only one size and spark plug wrenches tend to fit most applications
Step 5. Remove the spark plug with the wrench
Turn the key to the right until the spark plug is fully unscrewed. Next, slide the key out of the hole gently with the spark plug still inside.
If the spark plug is still hot, you can leave it on the key while you examine it
Part 3 of 3: Install New Spark Plugs
Step 1. Buy the correct type of spark plug
Talk to a local auto parts store clerk for help choosing the right spark plug for your engine. Spark plugs burn at varying degrees of intensity and it is important that you choose one designed for use in your vehicle.
- You can also find out which spark plug is right for your vehicle by consulting the service manual for your specific year, make, and model.
- Make sure to disconnect the battery before continuing.
Step 2. Use compressed air to clean the spark plug hole
Before installing the new spark plug, you can use compressed air from a can or an air compressor to clean out any dirt or debris that may be in the hole where you are inserting the spark plug. This will prevent something from falling into the engine and damaging it.
- Be very careful not to drop debris or small tools into the spark plug hole.
- An industrial vacuum may be a better option if debris has already fallen into the hole.
Step 3. Make sure the new plug has adequate clearance
The space on the shiny surface of the spark plug determines the length that is used to ignite the air and fuel within the engine. Use a gauge to get the correct gap between the spark plugs before installing them.
- Most gauge tools are shaped like a circle. Insert the edge of the circle into the gap between the spark plug and its glowing surface. Then rotate it until it reaches the space for your vehicle.
- Consult your vehicle's service manual to find the proper clearance for your engine.
Step 4. Insert the spark plug into the wrench
Insert the spark plug into the rubber boot inside the wrench. Then, connect the spark plug to an extension that is at least a few inches long. This will allow you to screw in the spark plug as if you were doing it with a screwdriver.
- Make sure the extension is long enough that you can screw the plug into place.
- Most spark plug tools use a 1 cm (3/8-inch) drive, so use a ratchet extension of the same size.
Step 5. Screw in the spark plug by hand
Turn the spark plug and extension clockwise without applying too much downward pressure. If you force the spark plug to screw in, you can cross the threads in the engine block, resulting in costly repairs.
- Turn the extension clockwise until the spark plug threads into place inside the engine.
- If it suddenly becomes hard and then easy to screw back into the spark plug, you should remove it and start over to avoid stringing it.
Step 6. Tighten the spark plug with a ratchet
Once the spark plug is hand-tightened inside the engine, connect a ratchet to the extension and tighten the plug slightly to make sure it doesn't vibrate out of place. You don't need to push the plug too hard to make sure it's a tight fit.
- Avoid over tightening the plug, as this can break it or make it difficult to remove.
- If you break a spark plug, you will need to have it removed by a professional.
Step 7. Reconnect the spark plug wire
Take the wire you disconnected from the previous spark plug and press it firmly into the back end of the now secured spark plug. The wire should fit into the spark plug when you feel it is firmly connected.
- You can choose to apply a small amount of electrical grease to the spark plug or wire to ensure a strong connection.
- Reconnect the battery once you're done.