The other weekend I changed the spark plugs on my 2009 Mazda6 3.7L V6. It wasn't as difficult as I had thought.I didn't take pictures of every single step, so in-between details were not photographed and should be relatively easy to figure out. This is a hastily put together DIY so I will likely edit it over the next few days for better clarity (also the game starts in a few minutes so I was trying to rush this
Old worn factory plugs at 72,643 miles:
The plugs were worn in my opinion, top ones are rear bank and measured .063, .065, and .080. Bottom ones are front bank and measured .068, .065 and .065. It's really hard to see in the photos but you can see where the ground has worn; it's the best I can do with my camera phone.
I replaced them with NGK Laser Iridiums versus going with the single platinum Motorcraft plugs, part# 5367 or ILTR6B11 NGK Laser Iridium 5367 ILTR6B11
I got them from Rockauto [I know I linked to Amazon as it's easier for met to link to an Amazon product versus Rockauto] as they were the least expensive for all 6 after shipping compared to locally or on Amazon. The NGK plugs are pre-gapped at .044; I checked them all and they were spot on in my case. I did not take any pictures of the new plugs. Perhaps I will pull one of the front bank ones next week to check on it and take a picture then.
1. First things first, I let the engine cool down for about two hours; the engine was luke-warm to the touch at this point with it being about 70 degrees outside.
(As you can see, I already had removed the intake hose; I used a 5/16" socket on the hose clamps versus a flat-head screwdriver. The hose flexes, so compress/flex it so you can remove it).
2. Remove the engine cover; to do this you will need to remove the oil fill cap, then lift off the cover. In the engine bay photo, you can see where the ball-studs of the cover go into rubber holes on the intake [circled in GREEN, and the one ball-stud circled in WHITE], simply pull up until it releases.
3. Remove the breather hose that goes from the intake hose to the valve cover then remove the intake to airbox hose. To do this, you'll notice these clips:
Position the clip as such; don't bend it too much or it may break, just enough to clear the retention ridge and the hose should pull off with minimal force.
3.1 Disconnect the PCV hose, brake booster hose [Circled in RED on photo]. For the these hoses, you'll have to get the spring clamp with some pliers and then wiggle the rubber hose off the intake portion. It can be a little difficult so I usually use a wiggle/twist motion and sometimes pliers to loosen the initial hold.
PCV hose connection up close
Brake booster vacuum hose and additional vacuum hose up close
3.2 For the TB vacuum line and the TB connector [circled in BLUE], you'll notice the red lock portion on the electrical connector, and a blue retention clip on the vacuum line. On the electrical connector, you'll lift the red part up into the unlock position and this will allow you to press on the release portion of the clip so you can pull it off the connector. Be carefull pulling on the red tab, it is possible to pull it too far and they can break from being brittle from engine heat. The blue retention clip on the vacuum line is somewhat the same; you lift the blue portion to the unlock position and then gently pull the hose off.
4. Electrical harness on intake. In the engine bay photo, you'll have noticed three gray zip-tie clips that hold the electrical harness onto the intake. These can be removed by pressing in the wedged part underneath to release the clips from the hole. I usually press one part in, lift, and then press the other end in. If you have needle-nose pliers this may help. For the clip on the far right, I found it far easier to just cut the electrical tape that was holding the harness to the plastic bracket; I tried pulling the clip out of the hole but it was not going to come out. You can re-tape the harness later on, however, I found it unecesarry as the other three zip-clips hold the harness in place quite well.
5. Bolts that hold the intake. In the photo you'll notice 8 bolts circled in yellow, with one hidden under the throttle body. I used a 5/16" deep socket on a 1/4"-drive ratchet; I believe an 8mm would work as well. The one nearest the firewall doesn't come all the way out of the hole as it has a rubber damper/retention system so just loosen this one all the way out. The one in the middle of the intake is the longer one and will be quite obvious which goes where as the others (besides the TB one) are the same size.
This is the bolt hidden under the TB. In order to prevent the bolt from falling out of the socket when loosening or tightening, I used a piece of blue paper shop towel to secure the bolt into the socket. Once you have all 8 bolts out, you should be able to pull off the intake; you may have to wiggle it out from getting caught in the harness or whatnot.
Do be sure to cover up the runners/plenum to prevent debris from falling in. I folded a couple blue shop paper towels to cover it up while I worked. (sorry I don't know what the correct terminology is when the intake is split like this).
Underside of intake showing gasket:
I believe the factory procedure advises to replace these three rubber gaskets when removing the intake, however, mine were still very pliable and no cuts or nicks so I decided to reuse the old gaskets. I did however clean the mating surfaces.
6. Remove clips from coils. To do this, you'll slide the red lock into the unlock position and then press on the clip to release it from the coil [press on the black portion of the clip directly under where the flat head is in the picture] These can be pesky so I used a flat head screwdriver to tap them out. Be careful doing it this way; I broke one lock clip as I backed it out too far. The clip still clicks and secures onto the coil plug connector however.
For the next portion, I did it one cylinder at a time [except that I removed all the coil bolts at once, as well as disconnected all the clips], primarily to keep each coil with it's cylinder without having to mark each one if I were to remove the coils all at once.
7. I don't exactly recall what size bolt holds the coils in place. Remove the bolt, and then remove the coil. From the factory, they may have used dielectric grease, which is good, however, in my case, it created somewhat of a vacuum that made it a little more difficult to pull the coils off. These coils don't seem to clip onto the spark plug, rather, there is a spring and the coil bolt holds it in place. I used a combination of a twisting motion and lifting, along with very careful prying [with a plastic pry tool] under the bolt hole to lift the coils off.
7.1 Remove spark plug. These are tapered seat spark plugs. Thankfully none of mine were difficult to remove.
7.2 Replace spark plug. For tightening, I honestly don't know what the torque specification is, however, I have installed tapered seat before on previous vehicles and small engines, and I have had no problems using 1/32-1/16 [as NGK depicts on the package] of a turn after the seat contacts. It's more of a feel thing for me. Certainly don't crank on this with a 2-foot breaker bar or anything like that. If you're unsure about it, use a torque wrench.
7.3 Replace the coil. For tightening the coil bolt, I used a 1/4"-drive raatchet and tightened snug, probably 1/16 to 1/8 turn after it contacts.
After replacing all the spark plugs, start putting things back in the reversal of removal. Getting the manifold to line up correctly can be tricky; you will likely have to wiggle it back into place so it sits flat. There are some alignment pegs that help with this so make sure these go into there recesses if you're having trouble aligning it. Don't forget to reconnect the TB electrical connector.
When tightening the manifold back down, go in a star pattern, that is, I started from the middle, then an opposite corner, etc. doing the firewall bracket bolt and the bolt under the TB last [Don't forget the one under the TB, I did and had to remove the intake hose again to get it back in. Use a little piece of paper to wedge the bolt to the socket so it doesn't fall out] I did not use a torque wrench on these; I went snugged up plus an additional 1/8-1/4 turn. I realize it's not best practice to not torque fasteners.