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Old 03-24-2020, 02:39 PM   #1
cederholm
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Default how to bench test a coil??

I'm having starting issue and I don't think I'm getting spark. How do I bench test a coil?

Thanks all.
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Old 03-24-2020, 03:51 PM   #2
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Default Re: how to bench test a coil??

I found this,

https://www.yesterdaystractors.com/c...mall&th=786236

...and I'm not getting a reading on the secondary winding. I think I have a 6v coil kicking around from an old Chevy, any reason I couldn't use that?

Thank again,
Carl
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Old 03-24-2020, 03:52 PM   #3
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Default Re: how to bench test a coil??

This might be the information your looking for

https://fordbarn.com/forum/showthread.php?t=148526
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Old 03-24-2020, 04:17 PM   #4
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Default Re: how to bench test a coil??

Perfect! Thanks
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Old 03-24-2020, 06:21 PM   #5
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Default Re: how to bench test a coil??

The primary should measure 1.4 ohms. Opening and closing points manually will show if you have the high tension side working with ignition switch on points shorted and then opened. My bet is you have other issues. Do you know how to use a volt ohm meter ?
You can quickly troubleshoot, especially if you have no spark.
With points open and ignition switch on you should have relatively the same voltage at the starter switch, both side of coil, both terminals of junction box, and the moveable point arm
Points open as stated. It should be within a 10th of a volt or so. If not find what the problem is with your meter.
Update you post and let us know what you have following the checks.
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Old 03-25-2020, 08:55 AM   #6
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Default Re: how to bench test a coil??

Thanks Larry,

Not sure if I fully follow you but this is what I have so far.

Using my multimeter I have 1.5 ohms across the primary circuit and no reading across the secondary from either of the small posts.

If I understand you correctly you're saying with ignition on I should get a voltage reading from the secondary post of the coil. And then in turn the same reading at the distributor, both primary circuits, the starer switch and junction box.

Thanks for our help,
Carl


Quote:
Originally Posted by larrys40 View Post
The primary should measure 1.4 ohms. Opening and closing points manually will show if you have the high tension side working with ignition switch on points shorted and then opened. My bet is you have other issues. Do you know how to use a volt ohm meter ?
You can quickly troubleshoot, especially if you have no spark.
With points open and ignition switch on you should have relatively the same voltage at the starter switch, both side of coil, both terminals of junction box, and the moveable point arm
Points open as stated. It should be within a 10th of a volt or so. If not find what the problem is with your meter.
Update you post and let us know what you have following the checks.
Larry Shepard
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Old 03-25-2020, 10:02 AM   #7
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Default Re: how to bench test a coil??

Number one, its easy to test for spark. With the hood open, stand on the left side of the car and pull a spark plug strap about a 1/4 inch off the top of a plug and with ignition on, push starter rod with your hand. Should see a nice blue spark with engine cranking. If not, put a voltmeter ACROSS the two primary screws on the coil, turn engine over slowly by hand, you should see the voltage go from battery to zero as the points open/close. If you don't, first thing to do is clean points. Then check again.
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Old 03-25-2020, 10:27 AM   #8
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Default Re: how to bench test a coil??

Very helpful, I'll check and report back.

Thanks,
Carl

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Originally Posted by eagle View Post
Number one, its easy to test for spark. With the hood open, stand on the left side of the car and pull a spark plug strap about a 1/4 inch off the top of a plug and with ignition on, push starter rod with your hand. Should see a nice blue spark with engine cranking. If not, put a voltmeter ACROSS the two primary screws on the coil, turn engine over slowly by hand, you should see the voltage go from battery to zero as the points open/close. If you don't, first thing to do is clean points. Then check again.
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Old 03-25-2020, 11:33 AM   #9
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Default Re: how to bench test a coil??

I HAVE spark! ...but it still wont fire. Not even with a good dose of starter fluid.

Hmmm, back to the drawing board.
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Old 03-25-2020, 11:44 AM   #10
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Default Re: how to bench test a coil??

Check your spark plugs they maybe fouled. Replace if needed.
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Old 03-25-2020, 11:49 AM   #11
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Default Re: how to bench test a coil??

They are clean and dry. Had a little carbon soot but I cleaned them.

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Check your spark plugs they maybe fouled. Replace if needed.
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Old 03-25-2020, 12:03 PM   #12
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Default Re: how to bench test a coil??

Quote:
Originally Posted by cederholm View Post
I HAVE spark! ...but it still wont fire. Not even with a good dose of starter fluid.

Hmmm, back to the drawing board.
Great! Now you need to check if you have spark at the right TIME.
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Old 03-25-2020, 12:27 PM   #13
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Default Re: how to bench test a coil??

WooHoo!! She started and ran perfect - oh what a sweet sound.

One thing I found, the secondary terminal on the coil and the wire from it were rusted. I think that lead to a hard start and my flooding it. I still need to replace that wire, but I think cleaning it made a world of difference.

Thanks all,
Carl
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Old 03-25-2020, 12:50 PM   #14
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Default Re: how to bench test a coil??

Need compression also..bot a new 6v coil from major supplier would run good a idle but at road speed misfire ..took a while to figure this one out..don't buy new coils unless a name brand !! napa ,delco etc...better to find an old coil from the 50's.
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Old 03-25-2020, 05:59 PM   #15
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Default Re: how to bench test a coil??

Secondary coil winding is high resistance due to many fine windings. It has to be checked on a high ohm scale between the negative terminal and the coil tower terminal if the coil is marked correctly for negative ground polarity on a late type 1.5 ohm coil. It can be checked from either terminal but one will give the primary coil resistance added in and the other will just be the secondary coil reading. Small terminal to small terminal will just be the primary ohms reading either way.
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Old 03-25-2020, 06:09 PM   #16
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Default Re: how to bench test a coil??

I use and prefer the Pertronix Flame Thrower coil.
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