Miller Cycle Spark Plug Replacement
Note: While this guide illustrates EGR valve removal and rear intercooler removal, neither is required to perform a rear bank spark plug change. However, removal of one or both of these components may make getting to the rear bank plugs easier.
Click here for spark plug specifications.
Front Bank (and the basics)
First, remove the front intercooler. If you are unfamiliar with how to do this, view the Intercooler Removal & Cleaning Guide. Once the front intercooler is off, you’ll see the front bank spark plugs exposed.
Remove the wiring harness from the spark plug coil.
Remove the two retaining screws (8mm) holding the coil to the head.
Gently twist the coil and pull it straight out of spark plug tube.
Using a 5/8ths inch or 16mm spark plug socket and extension, remove the spark plug. Use caution, the plug threads may be seized in which it will be difficult to unscrew. Just take your time! I’ve broken the top ceramic part off of spark plugs before being too careless…tiny ceramic pieces are not fun to clean out of the tube!
I bought a “tune-up” kit at AutoZone. It includes anti-seize grease for the threads and a tube of silicon grease. The silicon grease is for the inside of the coil pack boot so it doesn’t get stuck to the ceramic top of the plug. Squeeze a little bit of the anti-seize compound and spread it on the threads. Then, put some of the silicon grease compound on the ceramic part of the plug and also some on the inner part of the boot. Avoid contaminating the electrode end with either of these compounds.
Once plug is prepared, screw it back into the spark plug hole making sure not to cross the threads. Crossing the threads will strip them and you DON’T want that. The spark plug should be able to be hand tightened until snug. If it is hard to turn, then the threads may be crossing. Tighten the spark plug using 11-16 ft/lbs of torque.
The process for changing the rear bank of spark plugs is usually the reason most people shy away from doing this themselves. There is a bunch of stuff in the way and it can become a little intimidating.
First, locate the wiring harness located directly above the rear bank of spark plugs. Each connector (circled in red) will have to be unplugged. There are more connectors than I have circled. I couldn’t get them all in the picture, so you’ll just have to look for them. I suggest marking each one so that you don’t get confused when hooking them back up.
Once the connectors are unplugged, you’ll need to remove the three bolts highlighted in yellow in order to get the whole thing out of the way.
Once the wiring harness is out of the way, if you look straight down through the hole it left behind, you’ll see a 6” rubber hose. You'll need to remove this hose by releasing the clamps on either side and pulling it free. Before you do, see the next step.
Removal of the EGR valve is optional. All three rear bank plugs can be changed without removing it, but the coolant hose pictured above needs to be removed in order to gain access to cylinder #3. Before you disconnect any hoses, remove the radiator cap to release any residual pressure. If you don’t do this, you’ll lose a lot more coolant onto the ground than necessary.
To remove the EGR valve, remove the coolant hoses (red) and vacuum line (yellow). More coolant will come out, so you may want to place a towel under the hoses to stop it from going everywhere.
Next, loosen the rear nut. (Not sure of the size, but it’s big. I didn’t have a metric wrench that would fit, so I used an adjustable crescent wrench) Do not remove the metal pipe that the nut holds in place on the EGR, you will do this only after all of the nuts have been removed.
Now remove the remaining two nuts.
Now that the EGR is unbolted, gently pull straight up off of the bolt studs and the rear pipe should come right out.
Here’s what it looks like removed.
Everything should be out of the way so we can now begin to remove the spark plugs.
Look down at the rear bank and you’ll see the three rear bank coil packs. Remove them just like you did for the front bank. Note that it’s going to be a little more difficult since it is hard to see down in there. I stood on a plastic milk crate from the side in order to get a better angle. If your knees and back can take the punishment and you aren't very heavy, you may consider laying a folded rug or stacked blankets on top of the engine and getting to the rear bank that way. The connector to coil pack #5 is easier to get to from the car battery side if the rear intercooler is removed, but it is also doable without removing the intercooler.
Some people have used a universal (flex) joint attachment in order to reach the #3 and #5 plug. I bought one, but ended up not using it. I found that I only had to use a longer extension (12”-14”) in order to reach it.
Here is a diagram detailing actual cylinder numbers (this is not the firing order…only which cylinders are which for reference). The timing and accessory belts are on the left.
Here are all of my plugs once they were removed. Notice how three of them are different…the rears were Champion and the fronts were NGK. Sheesh...lazy ass people kill me!
[Spark plug removal/installation guide by GSREX - forums.mazdaworld.org -- edited/formatted to HTML from original MS Word format]