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J.R., Small Engine Technician
Category: Small Engine
Satisfied Customers: 7445
Experience:  Owner of outdoor power equipment business, repairing all makes and models.
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How to measure resistance on an ignition coil, such as from

Customer Question

How to measure resistance on an ignition coil, such as from plug wire to coil ? Will this test the coil ?
Submitted: 7 years ago.
Category: Small Engine
Expert:  J.R. replied 7 years ago.
What make and model of engine are we dealing with?
Customer: replied 7 years ago.
Shindaiwa LT-20 Trimmer with a S20EL engine and a 70030-71600 ignition coil...I think. I cant get the plug to fire. I mounted the coil to another trimmer to see if the magnets would excite the coil to fire but nothing, I am wondering if the insulation has weakened inside the coil causing a short inside, although it measures high resistance 8K ohms I read 2 other small weed-trimmer coils at 5K ohms (different mfg) . Either Shindaiwa coils are a higher resistance or the insulation inside the unit has weakened? Maybe I just need to install a new coil.
Expert:  J.R. replied 7 years ago.
The only way to test the coil without an expensive ignition tester ($1000.00) is to unplug the small wire from the coil and then check for spark. If you do not have a good spark with the small wire unhooked, then the coil is likely bad.

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