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Mazda CX-9 Spark Plugs Replacement Guide
How to change the spark plugs in a 2nd generation 2016 to 2021 Mazda CX-9 with the Skyactiv-G 2.5L I4 engine.

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2019 CX-9 2.5L I4
Pull Off Engine Cover
Plastic Cover Removed
This automotive maintenance tutorial was specifically written to assist owners of the second generation 2016, 2017, 2018, 2019, 2020 and 2021 Mazda CX-9 SUV in checking or changing the spark plugs in the Skyactiv-G 2.5 liter turbocharged inline four cylinder engine.

Owners of other Mazda vehicles such as the CX-5, CX-3, CX-30, MX-30, CX-8, Mazda8 (MPV), MX-5 Miata, Mazda2 (Demio), Mazda3 (Axela), Mazda6 (Atenza) and Mazda5 (Premacy) may also find these DIY instructions to be helpful.

The OEM (original equipment manufacturer) spark plug part number is Mazda PY8V-18-110 (also known as # PY8V18110 or PY8V 18110).

The NGK part number is NGK DILKAR7M8 (also known as # NGK 90288).

The tools and other items needed to complete this procedure include an 8mm socket, a 10mm socket, a 1/4" drive ratchet, a 14mm spark plug socket (or a 9/16" spark plug socket), a 3/8" drive ratchet, an extension bar, a tube of dielectric grease and possibly also a plastic pry bar tool or a flat head screwdriver.

The first two steps are to open the hood and gently pull off the plastic engine cover.

Set the plastic engine cover aside in a safe place.


Skyactiv-G Turbocharged
Four Ignition Coils
Metal Bracket Over Coils
Once the engine cover has been removed, you'll be able to see the four black plastic ignition coils.

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 spark plug well.

The two center ignition coils are partially obstructed by a silver metal bracket.

The metal bracket is held in place by four bolts. Three of the bolts are 8mm and one is 10mm.

1st Bolt - Left Rear
2nd Bolt - Middle Left
3rd Bolt - Under Hose
From left to right, the first bolt is 8mm, the second bolt is 10mm, the third bolt is an 8mm and the final fourth bolt on the far right side of the bracket is another 8mm.
Loosen Counterclockwise
Remove First Bolt
4th Bolt - Right Side
Loosen the three smaller bolts by turning them in the counterclockwise direction with an 8mm socket and a 1/4" drive ratchet.

Set the three 8mm bolts aside in a safe place.

8mm Bolt
8mm Bolt
Small 8mm Removed
One 10mm Larger Bolt
10mm Bolt Removed
1 10mm & 3 8mm Bolts
Remove the larger bolt by turning it in the counterclockwise direction with the 10mm socket and a 1/4" or 3/8" drive ratchet.

Set the 10mm bolt aside with the three 8mm bolts.

Lift Up Metal Bracket
Push Down Release Tab
Use Plastic Pry Bar Tool
Lift up the metal bracket and push it back a bit so that the two center ignition coils are clear.

To help further reduce the risk of having debris or any other object fall down into the cylinder, I recommend only checking or changing one spark plug at a time.

Push in the release button on the black plastic electrical connector.

If the release tab is very stiff, you may need to use a plastic pry bar tool or a large flathead screwdriver to depress it.

Power Plug Disconnected
Loosen Counterclockwise
Ignition Coil Bolt Removed
Loosen the single silver metal bolt that secures the ignition coil in place by turning it in the counterclockwise direction with an 8mm socket and a 1/4" drive ratchet.

Set the ignition coil bolt aside in a safe place.

Lift Out Ignition Coil
Spark Plug Well
Loosen Counterclockwise
Gently rotate the ignition coil back and forth a few times to make sure the rubber dust boot is not stuck or "frozen" to the top of the old spark plug.

Set the ignition coil aside in a safe place.

If you see a CEL (check engine light) or SES (service engine soon) warning indicator on your SUV's gauge cluster, use an OBDII scanner (also known as an OBD2 scan tool) to check for an ignition coil related DTC (diagnostic trouble code) such as P0350, P0351, P0352, P0353 and P0354.

The OEM (original equipment manufacturer) ignition coil part number is Mazda PE2018100A also known as Delphi GN10625

(All of the information written on the side of the OEM coil was "GN10625 PE2018100 K6266 8X18 H6T61271".)

A few other compatible replacement ignition coils with their part numbers include the following: Beck Arnley 1788527, NGK 48895, Standard Motor Products UF656 and United Motor Products COP574.

Some of the most common symptoms of a failing or faulty ignition coil include misfiring, stalling, reduced fuel economy (lower MPG), backfiring, rough idling, loss of power and difficulty starting the engine.

If necessary, attach an extension bar to your 14mm spark plug socket and the 3/8" drive ratchet.

(A 9/16" spark plug socket will also work.)

If you have trouble removing the old spark plug, you can try spraying a very small amount of penetrating oil down into the spark plug well.

Allow the penetrating oil to seep into the threads and loosen any rust, sand or debris for about 10 to 15 minutes.

Detach Ratchet - Spin Out
Lift Out Old Spark Plug
Inspect Old Spark Plug
Once the old spark plug is loose, detach the ratchet.

Spin out the old plug the rest of the way by hand with the extension bar.

Carefully lift the old plug straight out of the well and detach it from the socket. Your socket should have a rubber insert or a strong magnet to hold the spark plug in place.

Inspect the condition of the old OEM spark plug.

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

If the electrode tip of the old spark plug appears to be ashy white, the engine might have experienced over heating at some point in the past.

Empty Spark Plug Well
Lower In New Spark Plug
Tighten Clockwise

If you have a spark plug gap gauge tool, check the gap on the new spark plugs.

The spark plug gap specification for the OEM NGK DILKAR7M8 (90288) spark plugs is 0.030".

Most spark plug manufacturers recommend that you do NOT apply anti-seize lubricant grease to the threads of the new spark plug. Anti-seize grease is a lubricant and can easily lead to over tightening.

Push the new spark plug into the socket.

Carefully lower the new spark plug down into the well. Try to avoid hitting the electrode tip against the side walls of the spark plug well or the cylinder head.

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

Attach the 3/8" drive ratchet and continue tightening the new spark in the clockwise direction until it is snug.

If you have a very reliable and sensitive torque wrench, the Mazda CX-9 shop manual specification for tightening the spark plugs is 14 lb-ft or 18.98 N-m.

If you insist on using a torque wrench, please verify the correct torque specifications for your vehicle.

Note - I have never used a torque wrench to tighten spark plugs.

The guideline to remember is that new plugs (with a new gasket / crush washer) should be tightened to about 3/8 of a turn past finger tight. You might actually feel when the new crush washer compresses / collapses.

If you are re-installing old plugs after checking their condition, just tighten them to about 1/4 of a turn past finger tight.

(The spark plug torque specification for the Mazda CX-5 with the Skyactiv-G 2.0L I4 engine is very similar at 12 to 14 lb-ft or 15 to 20 N-m.)

Try to avoid over tightening the spark plugs. They should be snug but not extremely tight.

Apply Dielectric Grease
Lower In Ignition Coil
Push In Ignition Coil
Apply some dielectric grease to the opening in the black rubber dust boot at the bottom of the ignition coil.

The dielectric grease will help ensure a more reliable electrical connection by preventing dust, debris and moisture from entering the dust boot.

Lower the ignition coil down into the spark plug well.

Push down the ignition coil to make sure the rubber dust boot is secure over the top of the new spark plug.

Rotate the coil back and forth a few times to help spread around the dielectric grease.

Single Ignition Coil Bolt
Spin In Bolt Clockwise
Tighten 8mm Bolt
Line up the bolt hole in the ignition coil with the corresponding hole in the valve cover.

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
Replace 10mm Bolt
Tighten 10mm Clockwise
Push the electrical connector straight on to the ignition coil.

You should feel or hear the power plug "click" securely into place.

Spin In 8mm Bolt - Left
Tighten Bolt Clockwise
8mm Bolt Under Hose
Once you are done replacing or checking the spark plugs, lower the silver metal bracket back into place.

Spin in the three 8mm bolts and the one 10mm bolt a few turns by hand in the clockwise direction to make sure they don't become cross threaded.

Tighten 8mm Clockwise
Spin In Bolt By Hand
Tighten Clockwise

Double check that all of the bolts are tight before moving on to the next steps.

Metal Bracket Secured
Push On Plastic Cover
Spark Plug Change Done!
Lower the plastic cover down into place.

Push on the cover to secure the rubber friction fasteners to the metal pegs on the top of the engine.

Be sure to write down the spark plug change in your SUV's service records.

The maintenance schedule in the owner's manual specifies that the spark plugs should be changed every 40,000 miles (or every 64,000 km).

For more, please check out all of the 2016-2021 Mazda CX-9 DIY Repair & Maintenance Guides.

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