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?

  • 1
    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? Commented Jul 24, 2015 at 8:22

3 Answers 3


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.


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

  • Could you look at your answer and see if there is an issue there?? It really doesn't make sense. Thanks! Commented Jul 23, 2015 at 21:53
  • Ignition coils sorry Commented Jul 24, 2015 at 0:34

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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