# Diagnosing an Intermittent Ignition Coil



## timtenor (Dec 5, 2009)

I have a 1990 Maxima with the VG30E engine. It seems to have an interrmittent coil. The engine runs pretty well at startup, but then gets progressively worse as the engine warms up. I checked the input signal to the coil with an oscilloscope, and it has a steady, consistent periodic pulse waveform. But when I connect a timing light to the coil output, the strobe is not steady, but drops out intermittently, and the dropouts correspond to when the engine misses. So, is my coil bad, or am I fooling myself?

There are no codes set.


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## pulsar86 (Aug 13, 2009)

It does sound like a bad coil. If you have got a workshop manual you can check the coil resistance with a multimeter. If you havn't got the specs get an auto electrician to check the coil for you.


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## edge10 (May 25, 2008)

Somewhat old post, but in case you haven't fixed it yet: As above good place to start is the resistance spec of the primary and secondary. Coils usually fail by the insulation breakdown in windings (resistance lower than spec) or a open to the contacts (open circuit). Also, do a spark jump test - at .10 inch should be a blue snapping spark. Since the failure sound temperature dependend take a heat gun or hair dryer and heat the coil and do the test. Repeat test with a spray from a "cool can" from Radio Shack or electrical supply to get a temp cycle.


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