7 Symptoms of Bad Spark Plug And How to Change it?

What is a Spark plug?

Spark plug, also called Sparking Plug, device that fits into the cylinder head of an internal-combustion engine and carries two electrodes separated by an air gap, across which current from a high-tension ignition system discharges, to form a spark for igniting the air-fuel mixture.

The electrodes must be able to resist high temperatures, and the insulator separating them must withstand high temperatures and also an electric stress up to several thousand volts. Spark-gap length affects the energy of the spark, and the shape of the insulator affects the temperature of operation.

When too cool, operation leads to carbonization and short-circuiting of the gap; when too hot, there may be preignition.

How do spark plug works?

Electrical energy is transmitted through the spark plug, jumping the gap in the plugs firing end if the voltage supplied to the plug is high enough. This electrical spark ignites the gasoline/air mixture in the combustion chamber. The plug is connected to the high voltage generated by an ignition coil or magneto.

A spark plug is an electrical device that fits into the cylinder head of some internal combustion engines and ignites compressed aerosol gasoline by means of an electric spark. Spark plugs have an insulated center electrode connected by a heavily insulated wire to an ignition coil or magneto circuit on the outside, forming, with a grounded terminal on the base of the plug, a spark gap inside the cylinder.

Internal combustion engines can divide into spark-ignition engines, which require spark plugs to begin combustion, and compression-ignition engines (diesel engines), which compress the air and then inject diesel fuel into the heated compressed air mixture where it auto ignites. Compression-ignition engines may use glow plugs to improve cold-start characteristics.

The spark plug has two primary functions: To ignite the air/fuel mixture. Electrical energy is transmitted through the spark plug, jumping the gap in the plugs firing end if the voltage supplied to the plug is high enough. This electrical spark ignites the gasoline/air mixture in the combustion chamber. To remove heat from the combustion chamber.

Spark plugs cannot create heat, they can only remove heat. The temperature of the end of the plug\’s firing end must be kept low enough to prevent pre-ignition, but high enough to prevent fouling.

The spark plug works as a heat exchanger by pulling unwanted thermal energy from the combustion chamber and transferring heat to the engine’s cooling system. The heat range of a spark plug is defined as its ability to dissipate heat from the tip.

SPARK PLUG Construction:

Insulator

Insulates the terminal, center shaft and center electrode from the housing, preventing escape of high voltage from the electrodes.

Since the bottom of the insulator projects into the combustion chamber, high purity alumina with superior heat-proof characteristics, mechanical strength, excellent insulation and thermal conductivity at high temperature, etc. is used.

Terminal

The terminal connected to a high-tension cord through which high-voltage current from the ignition system flows. A terminal nut installed so this type can support almost any high-tension cord in the world. For vehicles not requiring a terminal nut, the terminal can be removed.

Ring, packing washer

Makes the insulator and the housing fit tightly to each other and maintains the airtightness.

Center shaft (stem)

Center shaft connecting the terminal and the center electrode. This shaft is made of steel and has the role of allowing high-voltage current to flow from the terminal to the center electrode without loss.

Housing

The housing forms an outer shell that surrounds the insulator, supports the insulator, and installs the spark plug in the engine. At the bottom the ground electrode is located, so current can flow through the engine itself to the center electrode over the gap.

Glass Seal

Mounted between the center shaft and insulator to maintain the airtightness. Denso uses the glass seal method. A special mixture of glass powder and copper powder is charged in the installation section for the insulator and center shaft and center electrode and melted at high temperature. This bonds the center shaft and the center electrode and fuses the insulator and the metal.

The sealing for both is good and the thermal ratio of expansion is appropriate, so even under harsh conditions gaps do not occur and good airtightness can be secured.

Gasket

Makes the housing and the engine fit tightly to each other and maintains the airtightness of the combustion chamber. There is a procedure for tightening and the appropriate tightening margin must be secured.

Electrode with copper

Special nickel alloy is used for the center electrode to reduce electrode wear. Copper is sealed into the center section to improve thermal conductivity.

Ring, packing washer

Makes the insulator and the housing fit tightly to each other and maintains the airtightness.

Center Electrode

A new iridium alloy tip with a diameter of 0.4 mm is laser welded to the tip of the center electrode to make the center electrode. This lowers the spark voltage, secures reliable spark, reduces the quenching effect, and improves ignition performance.

Iridium, like platinum, is a precious metal and has extraordinarily superior properties for a spark plug electrode, for example high-temperature withstand, high strength, and low resistance. In order to further improve oxidation resistance at high temperatures, Denso developed a unique new iridium alloy containing rhodium.

U-groove ground electrode

Nickel chrome material used for the ground electrode and various measures is taken with the shape to improve ignition performance.

One of these measures is the U-groove.

  • The surface contacted by the air-fuel mixture is large,
  • There is much edge section, and sparks occur easily.
  • The flame core (flame size) widens easily.

There are many other features as well and large ignition energy can be obtained. Denso obtained patents for spark plug U-grooves from 1975 to 1992.

Tapered cut ground electrode

The ground electrode has a shape in which the electrode tip is cut to a finely tapered shape. This reduces the quenching effect, so it improves ignition performance.

What Do Spark Plugs Do?

Your engine is a pretty remarkable machine, designed to turn an energy source (gasoline) into actual movement. But how does it do this? The answer is the principle known as internal combustion. In order to turn the fuel in your car from a source of potential energy into a source of kinetic energy, your engine needs to find a way to release it, and it does so through the combustion process.

The engine cycle is what makes this process happen. In your engine cycle, your valves fill your cylinder with a mixture of air and fuel, which are highly-explosive when combined. As the piston in your engine moves upward, it compresses this mixture until it’s in an extremely small space, creating even more potential energy.

At the peak of this compression, your engine ignites this mixture with a small spark, creating an explosion that forces the piston back downward, turning the crankshaft in your engine and creating the power which makes your car move forward.

Your spark plugs are what supply the spark that ignites the air/fuel mixture, creating the explosion which makes your engine produce power. These small but simple plugs create an arc of electricity across two leads that are not touching, but close enough together that electricity can jump the gap between them. Your spark plugs, along with the electrical and timing equipment which powers them, are part of what’s known as your ignition system.

Generally, your spark plugs made from extremely durable material, and capable of withstanding millions and millions of explosions before wearing out or needing to replace. But it’s true that over time, the explosions and corrosion lead to smaller or weaker sparks, which leads to reduced efficiency in your engine, and could lead to other issues including misfiring, or failure to fire.

What are the symptoms of bad spark plugs?

Engine Has A Rough Idle

If your Spark Plugs are failing your engine will sound rough and jittery when running at idle. This can cause vibrations to resonate through the vehicle which could cause further costly damage.

Trouble Starting

Car won’t start and you’re late for work… Flat battery? Low fuel? One often overlooked cause is Spark Plug failure. Without that crucial spark for ignition, you’ll be stuck where you are.

Engine Misfiring

When your engine misfires it momentarily cuts out and feels jerky because the cylinders are not firing correctly. This can lead to an uncomfortable ride and higher emissions.

Engine Surging

Again, this can lead to an uncomfortable – and potentially dangerous – ride. The engine is working inefficiently, sucking in more air than is usually needed in the combustion process, causing continual stop-start motions.

High Fuel Consumption

Are you filling up more than you used to? Failing Spark Plugs can really take a bite out of your fuel efficiency. A simple change of Spark Plugs could be the solution.

Lack Of Acceleration

If your vehicle feels unresponsive and the accelerator has lost its sensitivity you might consider a service with a change of Spark Plugs to get things up to speed again.

What are the costs of replacing your spark plugs?

The cost depends entirely on the make of your vehicle. Some have more cylinders than others do. One way to count the number of spark plugs in your car is to count the cylinders. However, some cars have dual spark system. An example is a V4 engine that has four cylinders. Each cylinder has two spark plugs.

Regardless of the number of cylinders, your car has, replacing your spark plugs is usually cheap. One spark plug piece costs less than 10 dollars. Replacing all plugs plus labor for the mechanic should be between $40 -$150. It is not a complicated process; hence, it should take the mechanic an hour or less.

When Do I Replace My Spark plugs?

Spark plugs will serve you for many years and miles without the need to change them. However, motor manufacturers recommend you change them after every 30,000 miles.

How long a spark plug lasts depends on the type of the plug. Copper spark plugs have a short life compared to platinum or iridium.

Always replace spark plugs with the manufacturer’s original choice. If you cannot find the same spark plug, then replace it with high-quality spark plugs. Copper plugs are substandard and will wear off fast.

How to Change Spark plugs?

Changing spark plugs takes about an hour (for a four-cylinder engine) and will save you at least a hundred bucks in labor if you do it yourself. In most cases it’s a simple job that will help to maintain peak performance and the highest possible gas mileage.

Tools Required

  • gap gauge
  • Needle-nose pliers
  • Rags
  • Socket/ratchet set
  • spark plug wire puller
  • swivel socket.
  • Torque wrench

Step-1: Do it Yourself or Take it to a Pro?

The answer depends on the type of engine in your vehicle. Some V-6 models require removing portions of the intake manifold to replace the park plugs. If you’re not comfortable with that, take your vehicle to a pro. But if your engine affords easy access to the rear bank, you can probably do the job yourself. Just be sure you gap the spark plugs properly and use a torque wrench.

The tools shown are available at online suppliers and auto parts stores. While you’re there, ask the clerk for the spark plug gap and torque specifications for your vehicle. And buy a small packet of dielectric grease. It’s also important to ask about spark plug replacement cost before making an appointment.

Step-2: Open Up and Clean Your Work Area

Start by removing the plastic “vanity” cover (if equipped) and the air cleaner assembly from the top of the engine.

  • Label any vacuum hoses you remove so you restore them to the right place.
  • Pro tip: Learn the top of a four-cylinder engine, or the banks on a “V” engine, before you remove other parts.
  • Blast compressed air around the ignition coils to prevent crud from falling into the cylinders. Then blow any remaining loose dirt off the engine before you set out your tools and new plugs.

Step-3: Remove the Ignition Coil and/or Boot

  • Disconnect the ignition coil electrical connector by depressing (or pulling up) on the locking tab.
  • Rock the connector off the coil.
  • Remove the coil hold-down bolt and pull out the entire coil and boot assembly.
  • Pro tip: Some COP systems have a detachable rubber boot and spring. If they don’t come out with the coil, retrieve them with needle-nose pliers and replace them with new parts. Then remove the old spark plug.

If your car doesn’t have COP ignition, the spark plug wire will end in a boot that attaches to the spark plug. A spark plug wire puller makes it easy to pull the boot off.

Step-4: Unscrew the Plug

  • Blow away the dirt and grime that’s settled on and around the plug since it was installed.
  • Slide the proper size spark plug socket over the plug.
  • Pro tip: A swivel head spark plug socket makes the job much easier. You’ll probably need an extension of some length to reach the plug.
  • Rotate the plug counter-clockwise to loosen it.
  • Pro tip: Not all engines leave the plugs as accessible as shown here. The more compact the engine compartment, the harder it will be to get to the plugs. But all plugs can be removed.

Step-5: How To Gap a Spark Plug

Gap all plugs before installation using the manufacturer’s specs. Always check the spark plug gap before installing it.

  • Slide the correct wire gauge (or gap gauge) between the electrodes. The wire should drag slightly between them.
  • If the gap is too small, open it with the gap gauge by prying up.
  • If the gap is too large, tap the side electrode lightly on a solid surface.
  • Place a small dab of anti-seize compound on the plug threads and hand thread the plug into the cylinder head.

Step-6: Install the New Plug

Proper spark plug torque is critical in today’s engines.

  • Always use a torque wrench and the manufacturer’s spark plug torque specs. Insufficient torque can result in a plug blowing right out of the cylinder head, taking the threads with it. Too much torque distorts the plug.
  • If you used anti-seize compound on the plug threads, reduce torque by 10 percent. If you don’t have a torque wrench, go to the spark plug manufacturer’s website to find manual tightening techniques and spark plug torque specs.

Step-7: Lube the Spark Plug Boot and Button It Up

  • Apply a thin coating of dielectric grease around the inside of the spark plug boot before reinstalling the coil. The grease prevents misfires and makes it easier to remove the boot in the future.
  • Reinstall the ignition coil, hold-down bolt and coil electrical connector.
  • Reinstall the air cleaner and vanity cover and fire it up.

Tips for maintaining your spark plugs

Here you should consider preventative maintenance. Monitor your car closely to note changes. Keep looking out for the symptoms. It does not end at this point. Run a further diagnosis using these simple methods.

Inspect wires

Find a place with sufficient lighting and open under the hood of your car. Locate the spark plug wires and do a visual inspection. Look for damages to the cables. Scorch marks and cuts. Check for signs of corrosion.

Run your engine

Look out for electrical sounds. Listen to the sound from your engine. Noises may be from a high voltage leak.

Use water to spray the wires

Spray the areas where boots attach to spark plugs. If arcing occurs or the presence of mist switch off the engine. Remove the spark plug from the boot and look inside the boot for traces of carbon tracking. The presence of carbon tracking means that you will need to replace the spark plug.

Use a spark plug tester

A spark miss or spark misfire can make your engine lose its power and traces of black smoke from your exhaust. Run this checklist to know if you have a plug misfire.

  • Disconnect the spark plug from the spark plug lead
  • Connect your spark plug lead with your spark plug tester
  • Connect the spark plug to the spark plug tester and create a link from the spark plug to the lead.
  • Rerun your engine and listen for a gap of inconsistent timing.

Confirm if the wires to your spark plug are routed well.

Cross-cutting drains power from your car. If your vehicle has a manual, use it to determine which wire leads to which port.

Clean your spark plugs.

Disconnect the spark plug from the spark plug lead. Clean the spark plug thoroughly to avoid debris getting into the combustion chamber. Do not force or remove the spark plug with your hands. Use the spark plug socket wrench.

Use a spray and wire brush to remove any deposits. Never use an abrasive to clean your spark plugs.

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