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Checking ignition coils

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TERRY LAKER

04-17-2001 13:23:56

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can anyone tell me how you check coils on small engines? Some say it can be done with an ohm meter?

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Bob M

04-17-2001 18:01:32

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Re: checking ignition coils in reply to TERRY LAKER, 04-17-2001 13:23:56

Terry - Here's a rough guide for B&S and Tecumseh coils:

Primary to ground - a few tenths to about 5 ohms. Infinite or 0 resistance indicates an open or short circuit respectively

Secondary to ground - 2,000 to 3,000 ohms (it varies from coil to coil, also with temperature, but is usually around 2,700 ohms). Less than 2,000 indicates a short, and infinite resistance means an open.

To get good readings on the primary make sure EVERYTHING is disconnected - points, condenser, wiring to switch and interlocks, etc. - before testing.

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BS link

04-19-2001 08:32:44

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Re: Re: checking ignition coils in reply to Bob M, 04-17-2001 18:01:32

Link

Big Jake

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Al English

04-17-2001 21:01:13

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Re: Re: checking ignition coils in reply to Bob M, 04-17-2001 18:01:32

Hi Bob, The checks you described are worth doing. And, from the answer you gave I'm guessing you already know this. But, for the benefit of anyone else that's interested, if failing insulation on the coil windings is causing arcing within the coil, a coil tester that actually runs the coil is the only way of isolating the problem...Al English

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Bob M

04-18-2001 04:55:40

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Re: Re: Re: checking ignition coils in reply to Al English, 04-17-2001 21:01:13

Hi Al - You're absolutely right about the coil tester - thanks for reminding!

The ohmmeter tests will check only for opens/shorts in the windings - they won't detect high voltage breakdown of the internal insulation. Consequently a coil will occassionally appear "good" by the ohmmeter tests, yet still not fire. Swapping with a known good coil is the next step if you don't have a coil tester.

Bob M

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