Owners of other Mazda vehicles such as the Mazda2, Mazda5, Mazda6, MX-5 Miata, Mazdaspeed3, CX-5, CX-7, CX-9, MPV, Tribute, RX-8, Axela, Demio, Verisa, Premacy, and Atenza may also find these DIY instructions to be helpful.

The tools needed to complete this procedure include a 10mm deep well socket, a 14mm spark plug socket (or a 9/16" spark plug socket), a 6" extension bar, a 3/8" drive ratchet, dielectric grease, anti-seize lubricant (optional) and a spark plug gap gauge (optional).

A few compatible replacement 14mm size spark plugs for the SkyActiv-G 2.0L I4 engine with their part numbers include the following: NGK LKAR7BIX-11S (93501), Denso (4711) IXEH20TT, NGK 94124 ILKAR7L11 and Champion 9412.

Attention: Some Mazda3 vehicles are equipped with a variation of the 2.0L I4 engine that requires 5/8" sized spark plugs.

A few compatible replacement 5/8" size spark plugs are as follows: Denso (4718) ITV16TT, NGK (5019) LTR5G and Champion RE10PMC5 (3032),

Please double check the size of your old spark plugs and the OEM part number before purchasing new spark plugs.

You could also check the 8th digit of your VIN number but I would prefer to physically verify the old spark plug size and part number before buying new plugs.

Here are all of the possible variations of the 8th digit in your VIN number and their meaning: F = 2.0 non-Skyactiv (standard emissions), G = 2.0 non-Skyactiv (low emissions - California), 7 = 2.0 Skyactiv (standard emissions), 8 = 2.0 Skyactiv (low emissions - CA), P = 2.0 Skyactiv.

The engine cover is only held in place by a few rubber friction fasteners. Set the cover aside in a safe place.

If you have access to compressed air or a wet/dry shop vacuum, thoroughly clean off the top of the engine to prevent any debris from falling in to the spark plugs wells.

Press the release button on the electrical connector and slide it straight off the ignition coil. If you have trouble removing the power plug, you may need to use a flathead screwdriver to firmly press down the release tab.

I'd recommend checking or changing one spark plug at a time to further reduce the risk of dropping something in to the cylinder head.

Loosen the 5 nuts with the 10mm socket and ratcheting wrench by turning them counter clockwise.

There are four nuts along the top edge and one down below in the center.

Pull off the metal ignition coil retaining bracket.

Loosen the ignition coil bolt by turning it counter clockwise with the deep well 10mm socket and ratcheting wrench.

Rotate the ignition coil back and forth a few times to make sure the rubber boot is not stuck to the tip of the old spark plug.

Lift the ignition coil straight out of the spark plug well.

Carefully lower the spark plug socket down over the old spark plug.

Gently loosen the old spark plug by turning it counter clockwise.

If the spark plug won't turn, spray in some penetrating oil such as PB Blaster, Liquid Wrench or Kano Kroil and wait 15-30 minutes or more before trying again. If you don't have any penetrating oil, try spraying some WD-40 or just warm up the engine for a few minutes to expand the metal engine block.

Once the old spark plug is loose, detach the ratcheting wrench and spin it out by hand by turning the extension bar.

The OEM spark plugs on this 2012 Mazda3 are NGK brand and part number DILKAR7F8 (Mazda part # PE01-18110).

I plan on buying the NGK LKAR7BIX-11S (93501) iridium spark plugs since they have excellent reviews on Amazon and shouldn't need to be replaced for another 100,000 miles.

If the end of the old spark plug looks ashy white, the plugs may have been exposed to high temperatures such as engine overheating or they are the incorrect heat range for your driving conditions and/or environment.

If the old spark plugs are dark grey or covered in black soot, the engine may be burning oil and should be checked by a professional mechanic.

The new iridium tipped spark plugs should be pre-gapped from the factory. It is still a good idea to check that the gap is correct using a spark plug gap gauge disc. If the gap is not very close to the number specified on the manufacturers specifications, exchange the plug for a new one.

Insert the new spark plug in to the spark plug socket and make sure that the rubber insert or the magnet holds it securely.

An optional step is to apply a small amount of anti-seize lubricant to the upper threads of the new spark plug. This will make the plugs easier to remove if they are not replaced again for another 100,000 miles. Do not get any anti-seize on the electrode at the bottom of the new spark plug. Some spark plug manufacturers recommend against using anti-seize since it can lead to over tightening.

Push the new spark plug in to the socket attached to the extension bar.

Carefully lower the new spark plug down in to the well while trying to avoid hitting the electrode tip on the cylinder block.

Spin in the new spark plug by hand until it makes contact with the cylinder head to prevent it from becoming cross threaded.

Attach the 3/8" drive ratchet and carefully continue tightening the new plug until just past the point when you feel the crush washer at the top of the threads collapse.

Note - The Mazda3 service manual's torque specification for tightening the spark plugs is 12 to 14 lb-ft (or 15 to 20 N*m).

If you applied anti-seize lubricant to the threads, less force will be necessary to tighten the plugs. Do not over tighten the plugs to avoid cracking the ceramic part of the plug or stripping the aluminum threads in the cylinder head.

Double check that the new spark plug is tight before moving on to the next steps.

Apply a small amount of dielectric grease to the opening of the rubber dust boot at the bottom of the ignition coil. This will help prevent it from becoming stuck to the tip of the new spark plug and keep out any water or debris.

Lower the ignition coil down over the tip of the new spark plug and rotate it a few times to help distribute the dielectric grease.

Re-insert the 10mm ignition coil bolt and spin it in by hand a few turns to prevent it from becoming cross threaded.

Tighten the ignition coil bolt by turning it clockwise with the 10mm deep well socket and ratcheting wrench to just past hand tight. Do not over tighten the bolt to prevent from cracking the plastic ignition coil assembly.

Push on the power plug until it clicks securely in to place.

Tighten the 10mm nuts to just past hand tight.

Start the engine and listen closely for any strange sounds that might indicate a disconnected power plug or a loose spark plug.

If everything sounds normal, close the hood to finish the job.

For more, check out my other 2010-2013 Mazda Mazda3 Repair & Maintenance Guides.