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Mazda MX-5 Miata Spark Plugs Replacement Guide
How to check or change the spark plugs in the SkyActiv-G 2.0L I4 engine in a 4th generation 2016 to 2021 Miata.

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Paul B. Michaels
Author & Photographer
Auto Mechanic Since 1989

2018 Mazda Miata Engine
Four Ignition Coils
Sensor & Ignition Coil

This automotive maintenance tutorial was specifically written to assist owners of the 4th generation ND (2016, 2017, 2018, 2019, 2020 & 2021) Mazda MX-5 Miata in checking or changing the spark plugs in the SkyActiv-G 2.0 PE-VPS 2.0 liter inline four cylinder engine.

Owners of other Mazda vehicles such as the Mazda2 (Demio), Mazda3 (Axela), Mazda5, Mazda6 (Atenza), CX-3, CX-5, CX-7, CX-9, RX-8 and MPV may also find these DIY instructions to be helpful.

The original Mazda OEM spark plugs are part number Denso ZC20HPR11.

A few other compatible replacement iridium spark plugs with their part numbers are as follows: NGK 94124 ILKAR7L11, Denso (4711) IXEH20TT and NGK LKAR7BIX-11S (93501).

The tools needed to complete this procedure include an 8mm socket with a 1/4" drive ratchet, a 9/16" spark plug socket, an extension bar and a 3/8" drive ratchet.


Push In Release Tab
Use Plastic Pry Bar Tool
Disconnect Power Plug
If you have access to compressed air or a wet/dry shop vacuum, thoroughly clean off the top of the engine to help reduce the chance of having debris fall down into the engine when you check or change the plugs.

In order to check or change the first spark plug (located closest to the front of the vehicle), you'll need to disconnect the electrical connector for the sensor.

Push in the release tab on the ignition coil's electrical connector.

If you have trouble pushing in the release tab, use a plastic pry bar tool or a flathead screwdriver.

Slide the power plug straight off the base of the ignition coil housing.

Loosen Counterclockwise
Sensor Wire - Coil # 1
Single Bolt Removed

Loosen the single bolt that secures the ignition coil in place to the top of the engine by turning it in the counterclockwise direction with an 8mm socket and a 1/4" drive ratchet or an 8mm wrench.

Set the bolt aside in a safe place.

I'd recommend only checking or changing one spark plug at a time to help reduce the risk of having debris or any other foreign object fall down into the spark plug well or the cylinder head.

Pull Out Ignition Coil
Mazda P51B18100
Attach Spark Plug Socket
Gently rotate the ignition coil back and forth to make sure the rubber boot at the bottom of the spark plug is not stuck or "frozen" to the tip of the old spark plug.

If your vehicle is displaying a SES / CEL (service engine soon / check engine light) and an OBD2 Scanner indicates a DTC (diagnostic trouble code) that is related to the ignition coils such as P0350, P0351, P0352, P0353 or P0354, you may need to replace a faulty ignition coil.

The original OEM ignition coil part number is Mazda P51B18100 (also known as P51B-18-100 K6266 7Z20).

A compatible replacement aftermarket ignition coil is part number Spectra Premium C-995.

Attach the 9/16" sized spark plug socket to the extension bar and a 3/8" drive ratchet.

Lower the socket over the top of the old spark plug. Make sure the socket is securely attached to the top of the old plug.

Loosen the old spark plug by turning it in the counterclockwise direction.

If you have trouble loosening an old stubborn, stuck and/or rusted in place old spark plug, spray a small amount of penetrating oil into the spark plug well and allow it to seep into the threads for at least 5 to 10 minutes.


Spin Out Old Spark Plug
Inspect Old Spark Plug
Spin In New Spark Plug
Once the old spark plug is loose, detach the 3/8" ratchet from the extension bar.

Spin out the old spark plug the rest of the way by hand.

Carefully lift the old plug out of the well and detach it from the socket.

Inspect the old spark plug.

If the electrode tip of the old spark plug appears to be oily or covered in dark black soot, the engine may be burning oil and should be inspected a professional mechanic.

If the electrode tip of the old plug appears to be white or ashy, the engine may have experienced over heating.

I recommend buying the Denso (4711) IXEH20TT iridium tipped spark plugs since they have excellent reviews on Amazon.

The service interval or "service life" of the iridium tipped spark plugs is 75,000 miles. If you do any sort of racing such as autocross or drag racing, they should be checked and replaced more frequently. The owner's manual specification for the compatible spark plugs part numbers are PE5R-18-110 and PE5S-18-110.

Push the new spark plug into the socket. Your 9/16" spark plug socket should have a magnet or a rubber insert to securely hold the new plug in place.

Carefully lower the new spark plug down into the well.

Spin in the new plug a few turns by hand in the clockwise direction to help prevent it from becoming cross threaded.

Tighten New Spark Plug
Apply Dielectric Grease
Lower In Ignition Coil
Tighten the new spark plug in the clockwise direction to just a fraction of a turn past the point when you feel the new crush washer collapse.

Try to avoid over tightening the new spark plug to prevent from damaging the threads.

If you are re-installing an old spark plug, just tighten it to a tiny fraction of a turn past finger tight.

I've never used a torque wrench when replacing spark plugs, to prevent the costly mistake of over tightening them.

If you insist on using a torque wrench to tighten the spark plugs, the service manual specification range is 11 to 17 lb-ft of torque.

(An optional step that some mechanics in very cold climates or close to the ocean recommend is to apply a small amount of anti-seize lubricant to the threads on the new spark plugs to help prevent them from becoming corroded (rusted) in place. Most spark plug manufacturers do not recommend using anti-seize since it can easily lead to over tightening.)

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 in the rubber dust boot at the bottom of the ignition coil.

The dielectric grease will help keep out any debris, dust or moisture and ensure a reliable electrical connection.

Lower the ignition coil back down into the well and push it on to the tip of the new spark plug.

Line Up Bolt Hole
Spin In Silver Metal Bolt
Tighten Clockwise
Rotate the ignition coil back and forth a few times to help spread the dielectric grease.

Line up the bolt hole in the ignition coil assembly with the corresponding hole in the top of the engine.

Spin in the ignition coil bolt a few turns by hand in the clockwise direction to help prevent it from becoming cross threaded.

Tighten the bolt in the clockwise direction with the 8mm socket and a 1/4" drive ratchet until it is snug.

Try to avoid over tightening the bolt to prevent from cracking the plastic ignition coil housing.

Push On Power Plug
Ignition Coil Secured
Spark Plugs Replaced
Slide the electrical connector straight on to the base of the ignition coil.

The power plug should "click" securely into place.

Start the engine and listen closely for any strange noises that might indicate a problem such as loose spark plug or a disconnected ignition coil electrical connector.

Be sure to record the spark plug change in your vehicle's service records.

For more, check out all of my 2016-2021 Mazda MX-5 Miata DIY Repair & Maintenance Guides.

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