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About 8 months ago my engine light came on, and after pulling the code it was a misfire in cylinder 4. My vehicle is a 2004 Mazda MPV, and only has 60K miles on it. Everyone I talked to was skeptical that with so low of miles the spark plugs would be bad, so I just went ahead and replaced the ignition coil. Even though it looked OK, I replaced the spark plug in that cylinder anyway. To recap, I replaced the ignition coil, and plug in cylinder 4. Everything was great.

Fast forward to yesterday, and the engine light came on again. I expected it would be another misfire, and I would need to replace the ignition coil in another cylinder. To my surprise the problem is in cylinder 4 again.

Now, unless I happened to get a bad part, I assume the ignition coil is good. I pulled the plug that only has 5K miles on it, and it looks OK except the tip is slightly white. enter image description here.

I know if the tip is black/wet/oily it is sign of something else, but what about white? Usually brown means everything is OK, right?

question 1 Is this small amount of white normal with a plug with only a few thousand miles on it, or is an injector bad or something?

question 2 Assuming my coil, and plug are good, what are some other things I can look at that will be causing this misfire?

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    It may just be the angle of the photograph but the plug gap seems pretty big. What is that plug gap set to and what is the manufacturers specification?
    – Steve Matthews
    Jul 24, 2015 at 8:22

3 Answers 3

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Misfires can also be caused by fuel delivery problems. Such as a fuel injector with debris in it, or one that's sticking. Not all configurations of fuel injection will result in a misfire in just one cylinder though. Depends if your injectors are cylinder specific or batch fire into a common manifold.

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I asked mechanics and they say it's usually the ignition coils for a misfire.

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  • Could you look at your answer and see if there is an issue there?? It really doesn't make sense. Thanks!
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Jul 23, 2015 at 21:53
  • Ignition coils sorry
    – Jose Juan Ruvalcaba
    Jul 24, 2015 at 0:34
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Mine was just a spark plug cable that cracked at cylinder 2. I found out by pulling lightly on the cable and it easily broke off about halfway. Replaced cable, and engine ran fine. Planning to change all cables soon.

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