The first real part replacement was done on the Prius last night. Over the weekend, my wife was on the way home when the car started misfiring. The engine light turned on and it turned out to be a P0301 code (misfire on cylinder 1). Thankfully she was able to make it home. I checked it out, removed the coils and plugs. Most everything looked good, a bit of white/foamy gunk on 2 plugs (the top, not the business end). So I may have a bit of a gasket leak. I reassembled it all and went for a quick spin. It seemed fine... until it warmed up. Then it started doing it again. No engine code was set, so I ordered 4 new plugs and one coil pack. Last night I got the parts in the mail and went to town on it.
At first, the plugs appear to be pretty buried in there. But, the first step is to remove the 'relay' box. Two 10mm bolts and you can swing it out of the way.
With the relay box moved, you can actually get a wrench in to remove the coil packs.
And then its just a matter of removing the plugs. A 6" extension works well here, though there still isn't an over abundance of room.
I started with replacing all the plugs. They are the original Denso iridium plugs with 145k miles on them. They came out nicely and they all looked to be in good shape with a nice tan tip. This is one of the ones that had the stuff on it.
With the new plugs in, I buttoned it back up and went for a quick spin. It got up to temperature with no hiccups at all. So, it seems like it was a bad plug. Not too bad for 145k miles!