How to Change the Spark Plugs in Your Car’s Engine
Updated on February 21 2024
Gasoline engines all have spark plugs that ignite the air and fuel mixture inside your engine’s combustion chamber. When the spark plug ignites, it creates a mini-explosion that pushes the piston down. This action turns the crankshaft and turns the driving wheels to accelerate the vehicle. Without question, the spark plugs are essential parts of a gasoline car’s ignition system. When one or two spark plugs fail, it will cause the engine to misfire, leading to engine trouble and a host of annoying symptoms.
What are the signs of faulty spark plugs?
Watch out for these troubling symptoms. You may be dealing with faulty, defective, or worn-out spark plugs:
- Hard starting. A weak car battery is mostly to blame if the engine takes a while to start after cranking. But if the battery is solid, the next thing to check is the spark plugs. Remember that dirty or worn-out spark plugs will make it doubly challenging to start your car, especially during cold starts or cold weather.
- Rough idling. An engine that idles roughly could also be dealing with a defective fuel pump or a clogged throttle body. Also, you could be dealing with dirty or failing spark plugs.
- Engine misfiring. Bad spark plugs can cause engine misfires, leading to poor acceleration, bad idling, and excessive vibration when steeping on the gas pedal.
- Poor acceleration. If your car feels slower or sluggish than usual, a new set of spark plugs might be the cure. Keep in mind that a clogged air filter can also cause sluggish performance.
- Hesitation or surging. If you step on the gas and your car hesitates or surges when accelerating, you might want to consider changing the spark plugs before doing anything else.
- Mediocre fuel economy. If you notice your gas mileage is not what it used to be, consider changing the engine oil and the spark plugs. Worn-out plugs produce a weak or inadequate spark and will coax the engine to burn more gas.
Tip: When dealing with rough idling or hard starting, remember that a gasoline engine needs three critical elements to operate: air, fuel, and spark.
How to Change the Spark Plugs
- New spark plugs
- Ratchet and spark plug socket
- 10mm or 12mm wrench
- Anti-seize lubricant
- Penetrating oil (optional)
Step 1: Prepare the vehicle.
Park your car in a safe and level area, preferably inside a shaded garage whenever possible. Always work with a cool engine to avoid burns and scalds. If the engine is hot, pop open the hood and allow the motor to cool for 15 to 30 minutes before changing the spark plugs.
Step 2: Remove the engine cover and spark plug wires.
The next step is to remove the plastic engine cover (when applicable) to access the spark plug wires. Use a socket set or 10mm wrench to loosen the bolts that hold the plastic cover in place. Set the plastic cover aside.
Locate the spark plug wires above the engine. If you have a bigger V6 or V8 engine, you may need to remove more interference items to access the spark plug wires like the intake plenum, intake tube, etc. Grab the rubber boot of the spark plug wire, press firmly, and pull it out. You may need to twist the boot back and forth to loosen it from the spark plug underneath. If you damage the boot or see cracks or wear on the spark plug wires, replace the cables immediately.
On the other hand, if your car has ignition coils (or coil-on-plugs), loosen the bolts of each ignition coil using a socket set and pull it out gently. Other engines have ignition coils with locking tabs. Grab a flathead screwdriver and depress the locking tab before removing the ignition coils.
Step 3: Unscrew the spark plug.
Grab a ratchet and spark plug socket, insert the socket inside the spark plug hole, and turn counterclockwise to unscrew the spark plug. If you feel more resistance than usual when loosening the plugs, remove the spark plug socket and spray penetrating oil inside the spark plug hole. Allow to soak for five minutes and proceed in removing the spark plugs. Keep this in mind if your vehicle has an aluminum engine block.
Step 4: Install new spark plugs.
The next step is to install the new spark plugs one by one. Take the spark plug out of the box and gently drop it face down inside the spark plug hole. Grab the socket and tighten it using a clockwise motion. Do not overtighten the plugs! You can apply a small amount of anti-seize lubricant on the spark plug threads before installing each plug.
When buying new spark plugs, make sure to double-check the part number in the box. Using the wrong spark plugs could lead to minor issues later on, and some engines will persistently misfire. Check the owner’s manual to ensure you are buying and installing the right set of spark plugs for your car. It may not look like it, but there are many kinds of spark plugs in the market. If you have a newer car, the engine may need Iridium or Platinum spark plugs. Always insist on OEM spark plugs.
Step 5: Install the spark plug wires or ignition coils.
Reconnect the spark plug wires or ignition coils that correspond to each cylinder. Make sure not to mix up the cables to prevent misfiring or possibly damaging the engine. Now is also the perfect time to re-install the plastic engine cover.
Step 6: Start the engine.
The final step is to start the engine and check for signs of misfiring or hesitation. Allow the engine to warm up and take your car for a test drive.
Consider replacing the spark plugs every 20,000 to 25,000 kilometers. For vehicles equipped with long-life Platinum or Iridium spark plugs, you can change the plugs every 50,000 to 80,000 kilometers. Of course, not all cars are the same. Check the owner’s manual to be sure.