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How do you test an ignition coil?


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2013-09-02 13:06:00
2013-09-02 13:06:00

How to test an ignition coil

This testing procedure is valid for just about any automotive coil. Using an ohmmeter, check the resistance between the side terminals of the coil. Do this with all of the wires to the coil disconnected.

You should see 0.75 to 0.81 ohm of resistance. Then check the resistance between either side terminal and the center high tension terminal. The reading should be 10,000 to 11,000 ohms. Any significant deviation from these numbers would indicate that the coil could be defective.


You can also rest an ignition coil by using a volt meter.There should be a little over 12 volts pulse, or a dip and peak in the meter needle, rather than a steady 12 volts, at the output, while cranking the engine.


Be careful about these answers. My voltmeter has a 9 volt battery installed. An ignition coil can produce 20 kV - that is twenty thousand volts! - at 100 mW, now that would bother me a bit.

So now, how can we check this coil safely? Well, start by shorting the output (the high tension terminal) and check the primary winding for continuity. On a normal meter 0.75 ohms might be very hard to read but, if you use a 1.5 flashlight bulb and battery in series with it, if the bulb lights, the primary winding is probably ok. (Unless its insulation has got fried by a fault called a "shorted turn", in which case the flashlight bulb will still light up but the ignition coil still won't work...)

The secondary, high tension, winding of the coil can be checked by shorting it with a high resistance load having a tap to form a 1000:1 split ratio, so you can use your meter to check for an output voltage of around 20 volts when a small 1.25 volt battery is connected and disconnected to the primary.

The actual output voltage should let you work out the turns ratio between primary and secondary of the coil. maybe Note: to see the output voltage for a longer time, add a diode and capacitor onto voltage divider tap.
I need to know how to check a coil on a Honda accord 94


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