Coil testing

[pumper.atv 26]

:USA: How does a guy test a coil- have hade bad luck with coils on the farm and we just replace them casue we don't know how to test them :)

[Save Old Iron 1,563]

Start with visual inspection

Cracks, dents, leaks, severely corroded wire terminals and spark plug connection(s) - does it smell "burned"

Then some initial tests for resistance of the primary coil and resistance of the secondary coil

Tests are also possible for the "quality" values of the inductance of the wiring coils within the body. When a coil is struck by a rapid change in current, it "rings" electronically - like an oscillation in current flow

I said "rings" to give an idea relating it to the quality of a bell. A good bell, when struck, will ring for quite some time before dying out. So will a good coil, electrically that is.

Imagine a bell is cracked or you put you put your finger on the bell and strike it. The ring will die off rapidly. So will the ring or spark producing capacity of a coil if some but not all of the wiring inside the coil is shorted. It will "ring" or spark slightly, but not as much as a good coil.

The "quality" of a coil is not hard to check with the right tools, but this test is beyond the scope of a home user. I can cover this as a topic in a future session of SOI University if there is interest.

If you need to know how to check the coil with an ohmmeter, let me know. There should be plenty of sites on the internet for checking a standard ignition coil for proper resistance values.

[MikesRJ 552]

Testing the coil assumes you have already checked the other electrical components and adjustments. (i.e. Engine Timing - http://www.mywheelhorse.com/graphics/file/...gineTiming.pdf) and the points are gapped correctly per the timing and are in good condition. A new plug and inspection for obvious visual issues with wiring is sometimes in order as well. Don't overlook the obvious. The problem may be as simple as a loose or broken bad high-tension wire.

Here's two links for testing your coil:

Bench Testing (Meter Testing):

http://autorepair.about.com/od/troubleshoo...il-test-ohm.htm

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 is defective.

Manual (In-Circuit) Testing:

http://autorepair.about.com/od/troubleshoo...test-manual.htm