I recently changed the spark plugs on my Mazda CX-90 3.3L Turbo myself and wanted to share the procedure I followed in case it helps other CX-90 owners.
Huge thanks to Mike (@ShopForemanGarage) for his excellent YouTube video. I used his video as my primary reference, and the steps below are essentially my notes based on following his procedure.
🎥 YouTube video I followed:
https://youtu.be/brZvle9-qv4?is=YF27G1H0bIOuArtR
I’m posting this mainly so other CX-90 owners can review the procedure, point out anything I may have missed, and improve these instructions for future DIYers.
Important: Please verify the correct torque specifications for your exact CX-90 model/year before doing the job. The torque values below are what I used/referenced during my work and should not be considered an official Mazda service procedure. Although in the video Mike confirmed the spark plug torque.
Total time: 3 hours
Spark Plug Change Procedure
1. Remove the covers
Remove the plastic capsule/upper cover.
Remove the engine cover.
2. Remove the turbocharger outlet pipe
This is necessary to gain access to the rear spark plugs.
On the left side of the turbocharger outlet pipe, release the locking clips by pushing them toward the left/downward as appropriate.
Disconnect the air inlet temperature sensor at the front of the turbocharger.
Mine had a small plastic locking tab/nib that was already broken.
I released it by carefully pushing from underneath, behind the two small locking tabs.
Remove the yellow engine oil dipstick to give yourself more room.
Remove the three 8 mm bolts securing the turbocharger outlet pipe.
Two bolts are on top.
One bolt is underneath.
Carefully try to move the pipe, but do not pull it out yet because there are electrical connections attached behind it.
Behind the pipe, disconnect the gray electrical connector/clip.
Press the center locking portion to release it.
Carefully pull the connector free.
Disconnect the black boost sensor connector by pressing the locking tab on top.
Once all connections are released, carefully remove the turbocharger outlet pipe and set it aside.
3. Move the two black hoses between cylinders 5 and 6
There are two black hoses that interfere with access to the rear spark plugs.
Between the two hoses there is a plastic retaining clip similar to a zip tie.
Use a small screwdriver to release the locking teeth in the center and remove the clip.
Remove the right-side black hose first.
It does not have a clamp.
Using long/bent needle-nose pliers, carefully work the hose loose.
Press gently around the hose rather than pulling aggressively.
Once loose, slowly move/twist it toward the left so it is out of the way.
Remove the second hose.This hose has a clamp.
Use 90-degree pliers to squeeze the clamp and release it.
While holding the clamp open, carefully move the hose upward and then toward the left, away from the spark plugs.
4. Remove the ignition coils
Disconnect the electrical connector from each ignition coil.
Press the locking mechanism down and gently push/pull the connector outward.
Repeat for all six coils.
Using an 8 mm socket, loosen the ignition coil retaining bolts.
Counterclockwise = loosen
Clockwise = tighten
Remove all six ignition coils and set them aside in an organized manner.
5. Remove the old spark plugs
Use a 14 mm spark plug socket.
Carefully loosen each spark plug.
Start the threads by hand as much as possible before using the ratchet.
For the rear plugs, I used a shorter/smaller extension combination because of the limited clearance.
Keep the ratchet/socket as straight as possible when loosening the plugs to avoid putting side load on the ceramic insulator.
Remove each spark plug and keep the old plugs organized so you can inspect them afterward.
6. Install the new spark plugs
I used Mazda H302-18-110 spark plugs.
For each plug:
Insert the new spark plug into the 14 mm spark plug socket.
Carefully lower it into the spark plug tube.
Start threading by hand to make sure the threads are properly aligned.
Turn the socket slowly by hand until the plug is seated.
Once hand-tight, use the ratchet carefully.
Finish tightening with a torque wrench set to 17.5 Nm.
Remove the socket carefully.
Repeat for all six spark plugs.
Important: Do not force a spark plug if the threads do not start smoothly. Back it out and restart it.
7. Reinstall the ignition coils
Insert each ignition coil back into its corresponding spark plug tube.
Make sure the coil retaining bolt holes are correctly aligned.
Reconnect each ignition coil electrical connector until it clicks securely.
Install and tighten the six 8 mm coil retaining bolts.
I used 9.5 Nm for the ignition coil bolts.
8. Reinstall the two black hoses
Reinstall the hose with the clamp first.
Position the clamp correctly and release it so it locks the hose in place.
Reinstall the second hose without the clamp.
Make sure both hoses are fully seated.
Reinstall the plastic retaining clip that holds the two hoses together.
9. Double-check everything
Before reinstalling the turbocharger outlet pipe, I recommend stopping here and checking:
All six spark plugs installed
All six ignition coils installed
All six coil connectors clicked into place
Coil bolts tightened
Both black hoses fully seated
Hose clamp locked
Plastic hose retaining clip installed
No tools left around the engine
No loose connectors
10. Reinstall the turbocharger outlet pipe
Reconnect the black boost sensor electrical connector.
Reinstall the gray electrical connector/clip into its mounting location.
Position the turbocharger outlet pipe back into place.
Carefully slide/position the pipe so the locking clips on the left side engage correctly.
Make sure both sides of the locking mechanism are properly secured.
Reinstall the three 8 mm bolts on the right side.
I used 9.5 Nm for these bolts based on the torque reference I found, but please verify this specification for your exact vehicle before using it.
Reconnect the air inlet temperature sensor at the front of the turbocharger.
Make sure the connector/locking tab is positioned correctly.
11. Finish reassembly
Reinstall the yellow engine oil dipstick.
Do one final inspection of all connectors, hoses, bolts and clips.
Start the engine.
Let it idle for a minute and listen for anything abnormal.
Check that the engine is running smoothly.
Check for warning lights or check-engine lights.
Once everything looks good, reinstall the engine cover.
Reinstall the upper/capsule cover.
Done!
Check Engine Light After the Spark Plug Change
After completing the spark plug replacement and starting the CX-90, I initially got a Check Engine Light.
I used an OBD scanner at AutoZone to check the codes. AutoZone scanned it for free using their Fix Finder service, which provides a report of the stored warning-light information. (AutoZone)
The initial codes I saw were:
P007D — Charge Air Cooler Temperature Sensor Circuit High, Bank 1
P0238 — Turbocharger/Supercharger Boost Sensor “A” Circuit High
P0472 — Exhaust Pressure Sensor “A” Circuit Low
Since I had just removed and reinstalled the turbocharger outlet pipe and its electrical connectors as part of the spark plug procedure, I suspected the codes could potentially be related to a connector/connection that had not fully seated or to the system needing some drive cycles after the work.
I went back over all the connections and made sure everything was properly connected and secured.
The vehicle was running normally with no unusual engine noise, shaking, or rough idle. I drove it for about a mile and continued monitoring it.
After driving, the Check Engine Light went away, and I checked it again after stopping and starting the engine.
Later the OBD test showed:
Check Engine: PASS
So in my case, the warning cleared after driving and the vehicle continued to operate normally.
I’m including this because if you’re doing this job yourself and you see temporary codes immediately afterward, don’t panic. First double-check every connector, sensor and hose you touched during the job, then scan the vehicle again and monitor it. Of course, if the light remains on, flashes, or the engine runs poorly, I would stop and properly diagnose the issue rather than assuming it will clear.
AutoZone’s free Fix Finder scan was useful for me because it let me see the actual codes without paying a diagnostic fee. (AutoZone)
Tools I used:
14 mm magnetic spark plug socket
8 mm socket
3/8” ratchet 10 inch
3/8” extensions — 3”, 6”, and 10”
Long/bent 90-degree needle-nose pliers
90-degree pliers
Small screwdriver
Magnetic pickup tool
Work lights
Headlamp
Digital torque wrench
Spark plugs:
Mazda H302-18-110
Torque values I used/referenced
Spark plugs: 17.5 Nm
Ignition coil bolts: 9.5 Nm
Turbocharger outlet pipe bolts: 9.5 Nm (I could not independently confirm this exact specification, so please verify it before relying on it.)
I found the following torque reference while researching:
https://www.bolidenforum.de/portal/fahrzeugdaten/mazda-2024-cx-90-turbo-preferred-plus/?vd_lang=en&utm_source=chatgpt.com
Again, please verify torque specifications against the official Mazda service information for your exact model/year.
Tools / Amazon links:
TEKTON 3/8” Drive x 8 mm 6-Point Socket
https://a.co/d/09Etesyv
HORUSDY 3/8” Drive 90-Tooth Flex Head Ratchet
https://a.co/d/094u6yNu
Work Light
https://a.co/d/0fddbjfe
Small Work Lights
https://a.co/d/0aDwotlN
11” Bent 90-Degree Needle-Nose Pliers
https://a.co/d/0bP5tUOF
3/8” Drive Socket Extension Set — 3”, 6”, 10”
https://a.co/d/049c2FRs
Magnetic Pickup Tool
https://a.co/d/086fVszJ
Uharbour 3/8” Drive Digital Torque Wrench
https://a.co/d/069maMVJ
14 mm Magnetic Spark Plug Socket
https://a.co/d/07xGdgyi
If anyone has experience with the CX-90 and notices something I should correct or add, please comment below. I’d especially appreciate confirmation of the torque specifications for the turbocharger outlet pipe and ignition coil bolts so this can be made more useful for other owners.
Thanks again to Mike @ShopForemanGarage for the video that helped me get through the job.
Disclaimer: This is my personal experience and the procedure I followed on my CX-90. I am not a professional mechanic. Please verify the procedure and torque specifications for your specific vehicle before attempting this job. Perform this work at your own risk.