Driving home the other day I noticed some vibrations up front. Reminded me of out of balance wheels. Then the check engine light started blinking. Then it was on steady, then blink, then steady... Took it easy the rest of the way home. Code reader said P0138 Oxygen sensor circuit high voltage bank 1 sensor 2, and P0304 Cylinder 4 misfire detected. At home is where I saw the engine shaking and extra noise from it (visions of piston rod slapping around in there). Removed plugs (original? tough to get out!), compression tested all 4 cylinders (130 to 140), new spark plugs (had they been in there for 196K miles?). Start engine and same, shake shake with some extra noises that weren't there before (car just sitting in driveway). Anyone have ideas what it could be? What else I can look at/check/test/rule out/rule in before towing it to dealer for their diagnosis? $3000 hybrid battery installed 5000 miles ago (2 months).
Swap the spark igniters between cyl 1 and cyl 4, and see if the misfire moves to cylinder 1. If yes then replace the bad spark igniter. If no then look elsewhere, such as the cyl 4 fuel injector or perhaps a wiring harness connector fault.
Swapped coils 1 and 4, started vehicle, new check engine light came on. Now shows codes P0300 (Random misfire detected), and P0301 (Cylinder 1 misfire). Before tonights swap I saw a narrow narrow crack in part of the original #4 coil (no arcing signs though). I've a densco coil reserved/ordered ($83). Why densco over other brands though? Also, can one misfiring cylinder cause the engine to shake and sound like there's something loose in the upper area of the engine? The sound and "inner feeling" is that it's coming from the head (upper, above pistons, valves/cams area) and at the cylinder 4 area (drivers side).
Changes the coil and your problems will go away. You use denso because all the other coils are the same brand, no compatibility issues
Installed the new coil last night and was quite happy that the shaking and extra alarming noise went away. Smooth running engine again, no shake, no "banging" noises. I've seen engines get the shakes when you pull a plug wire when they are running, but I've never heard the "banging" noise that I heard from the Prius. Felt good to feel confident in my "ride" again going to work today! Thanks for the inputs!
Another note about the "why Denso" question. I have a 2004 accord that I recently (25k miles ago) did a coil swap on. The original coils were on their way out after 175k. My options were Denso or Nippon for about $80 a coil, or try a no-name coil for $120 total for all six. Just for the fun of it, I went with the $120 option, and the coils just failed this past weekend (again, after 25k). The originals were Denso's, and even though they cost 4x more, they lasted 7x longer. I know this is anecdotal, but there are certain things it pays to skimp on. Coils aren't one of them, in my experience.
