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rotorwrench · 08-05-2021, 07:56 AM

The best way to test a coil is with an oscilloscope. It can be warmed up by powering it up like an electromagnet till its warm but not too hot. A function check should result in a nice blue spark if polarity is correct.

Most coil resistances of primary side checks should at least be within 10% of nominal 1.5 Ohm value. Heating up an old coil of unknown condition can result in open circuit when the wire expands and a crack opens up. An internal wire to wire short in a coil can reduce the resistance. A cracked wire can increase resistance and cause higher operating temperatures as well as intermittent opens after warm up.

08-05-2021, 07:56 AM	#11
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 16,440	Re: Ignition coils too far out of range? The best way to test a coil is with an oscilloscope. It can be warmed up by powering it up like an electromagnet till its warm but not too hot. A function check should result in a nice blue spark if polarity is correct. Most coil resistances of primary side checks should at least be within 10% of nominal 1.5 Ohm value. Heating up an old coil of unknown condition can result in open circuit when the wire expands and a crack opens up. An internal wire to wire short in a coil can reduce the resistance. A cracked wire can increase resistance and cause higher operating temperatures as well as intermittent opens after warm up.