Our friends 2010 Subaru Forester started throwing a PO301 code which is typically a misfire code. After checking the code, with our trusty code reader, it was in fact the misfire for cylinder number 1. So we ordered some plugs and coil packs for the car and planned to get to work.
Well, the first obstacle was that this particular 2010 Subaru Forester does not have a coil on plug setup. It has a master coil and uses plug wires to fire off the spark plugs. No big deal, my friend can just return the coils and recoup that money. So we decided to replace the plugs and be done with the project.
You can replace the driver’s side spark plugs pretty easily, you just need to pull off the plug wire and remove the spark plug. It’s a little tricky to do this but if you have a 5/8 spark plug socket, and two small extensions, you can get it done. The trick is to slide the socket and one extension into the bore, and then attach the second extension. You can then get the socket on the plug and remove it. You will need to pull the same trick on the way out in reverse order.
So we replace the plugs on the driver’s side and move on to the passenger side of the vehicle. This is a little more difficult because you will need to remove the air box to get to the plugs. This is how you do it.
First you remove the plastic air shroud that is connected to the air box. There are two plastic clips that are holding it in place (this particular car did not have them) that will need to be removed. You will then lift the plastic shroud up and out of the car.
Disconnect the Mass Air Flow sensor by pushing down on the clip and pulling it straight out.
Loosen the two clamps for the air intake with a flat head screwdriver and remove it. I did not get a picture of the Throttle Body side clamp.
Lift up the two metal clips that hold the air filter in place. Then remove the back side of the air box.
Remove the anchor bolt to the air box, it is a 10mm. I’m calling the one on the bottom the anchor bolt.
Remove the upper bracket that holds the air box in place. There are 2 10mm nuts that you will need to remove. I found it easiest to use an open ended wrench to accomplish this.
Once the nuts are removed, you will be able to slide the bracket off and manipulate the entire air box assembly out of the vehicle. Be careful, there is another piece that is dropped down through the body that will be coming out with it. Just maneuver the air box around to get it out.
This is where we found the issue with Cylinder 1. Taking the spark plug boot off the plug was pretty easy and felt just like all the others, but when trying to get the socket on the plug, I was unable to and found the contact that was supposed to be in the plug boot still attached to the plug.
I had to stick my head in the vacated spot to see that it was my problem. I used a pair of needle nose pliers to pull the broken contact off the plug and was able to get the plug out.
At this point, we needed to purchase new wires. My local auto parts store had a set and we replaced them.
The spark plug wires are super easy to replace, just do them one at a time so the order does not get messed up. Lay the new ones down on the ground so you can match the lengths of the ones you take off. I needed to remove the vacuum hose that was on the plenum to get the rear plugs off the coil, but once removed they came off without too much fuss.
Once the wires are replaced, make sure you put that vacuum hose back and re-assemble the air intake in the reverse order of disassembly.