Testing a coil with a Multimeter

Ara Klujian

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Jun 19, 2008
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#1
Their are primary and secondary fields on the coil. The primary field is the positive side and negative side. that field wires connect to. Take a multimeter and hook neg to neg and pos to pos in Ohm setting with coil disconected from all field wires. If the multimeter stays at a steady resistance without jumping from OL to high or low to high. The coil is good at a steady reading. Next take the MM and connest one end to the pos side on coil and the other to probe the secondary side and check the same resistance. The same principal applies with readings. Finally the negative side. Same thing repeat proceedure. If the coil fails to pass proper resistance it is bad.
You may encounter a coil that shows steady resistance at a non specification level. If this happens it may be the wrong coil for that engine or it may still be considered faulty. This is why it is important to know the specs. I've encountered this before.
 

Larry Cobb

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#2
Ara;

Meter testing is a good initial test procedure.

Coils can however, break down when they get hot.

This requires actual spark-gap testing with the engine up to operating temperature.

Take an old spark plug and increase to gap to 1/5 of an inch.

Turn the engine over with the gapped plug on each side.

Compare each coil output.

Larry
 
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JDARNOLD

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#3
You can also get a couple of inline spark testers from harbor freight, run the unit and compare the spark from side to side.