Cap & Rotor

[name]

I disagree, I have seen the insulation material crack and split and then they arc out internally.

I am the third owner of this vehicle, when I pulled the coil out to give myself some room when dealing with the ICM, I noticed it was mounted on the bracket with hex cap screws instead of being rivited, there also were no GM markings on it so I suspect it was changed out by a previous owner for whatever reason.

If it is arcing out internally, what would the symptoms be ?

 

[L31MaxExpress]

I am the third owner of this vehicle, when I pulled the coil out to give myself some room when dealing with the ICM, I noticed it was mounted on the bracket with hex cap screws instead of being rivited, there also were no GM markings on it so I suspect it was changed out by a previous owner for whatever reason.

If it is arcing out internally, what would the symptoms be ?

Mine was down on power, idled rough, then in the middle of a rainy/snow storm it quit firing completely. I did not even notice it had been down on power until I changed the coil out.

 

[name]

This kinda sounds familiar, The reason why I did a tune up was because I was having trouble getting up to speed to get on the Ohio Turn Pike ( 70 MPH ) But I just figured it was because of the plugs, wires, cap and rotor had 50K miles on them.

I took the coil to Autozone to have it checked but they said they could not do it .

 

[Scooterwrench]

There is probably no bench test for a coil with an internal crack. Only way to test that would be with an oscilloscope while running.

 

[Scooterwrench]

Mine was down on power, idled rough, then in the middle of a rainy/snow storm it quit firing completely. I did not even notice it had been down on power until I changed the coil out.

I had that happen once on a 78 Sportster. Bike ran great. I rode through a rainstorm and it didn't show a problem until I shut it off. Stopped at a buddies house and went I went to fire up and leave the starter said stay right here-stay right here-stay right here. Diagnosed no spark and determined it was the coil. When I pulled the coil off there was a crack in the backside. I figure water was laying in that crack and when I shut the bike off and the coil cooled it drew the water in and that was it,stay right here!

 

[name]

There is probably no bench test for a coil with an internal crack. Only way to test that would be with an oscilloscope while running.

Did a quick search on how to test with an ohm meter, low side is reading .5 high side is reading 8.34 . I do not know if these numbers indicate a bad coil on their own or not because I do not know what they should read. I do understand that this test may not be absolute .

 

[Caman96]

I bench tested this coil.

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Using this test, can’t remember the exact readings, but they were in spec according to this video.

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I can’t confirm or deny this test is legitimate or not, I’ve heard both on this forum.

 

[Schurkey]

There is probably no bench test for a coil with an internal crack. Only way to test that would be with an oscilloscope while running.

An automotive oscilloscope is the BEST way, but not the only way. And not many folks have a suitable 'scope.

Did a quick search on how to test with an ohm meter, low side is reading .5 high side is reading 8.34 . I do not know if these numbers indicate a bad coil on their own or not because I do not know what they should read. I do understand that this test may not be absolute .

The practical way (no oscilloscope) way to test a coil is to first make a visual examination for cracks/carbon tracks, then perform all the ohmmeter tests, then verify spark power using a spark tester calibrated for HEI ignitions.

If it passes ALL the visual and ohmmeter tests, AND can reliably fire the spark tester (preferably with the coil hot, and misted with water from a squirt-bottle) then the coil should be good.

Ohmmeter tests--specs are in the service manual:
Primary resistance
Secondary resistance
Primary to ground (should be infinite resistance--open circuit.)
Secondary to ground (should be infinite resistance--open circuit.)

SOME coils have the primary and secondary windings entirely separate; most coils have a connection between primary and secondary, so there's only one "ground" test needed.

The spark tester needs an actual spark gap. Avoid any "spark tester" that makes a light-bulb glow to indicate spark power.

 

[Scooterwrench]

If it passes ALL the visual and ohmmeter tests, AND can reliably fire the spark tester (preferably with the coil hot, and misted with water from a squirt-bottle) then the coil should be good.

That's a good test,didn't think of that.

The spark tester needs an actual spark gap. Avoid any "spark tester" that makes a light-bulb glow to indicate spark power.

Pretty hot new spark plug(long center electrode)with the ground terminal cut off and filed flush with the shell makes a good spark tester. If it jumps a fat blue spark across that your good to go.

 

[Schurkey]

Pretty hot new spark plug(long center electrode)with the ground terminal cut off and filed flush with the shell makes a good spark tester. If it jumps a fat blue spark across that your good to go.

Need a convenient way to ground the plug shell. Adequate for conventional, ballast-resistor systems. Not at all optimum for for non-ballast-resistor systems such as HEI. Doesn't have a big-enough spark gap to properly load an HEI coil.

I use a pair of spark testers. One for ballast-resistor systems (Points, old Chrysler electronic) and one for systems that don't use a ballast resistor (HEI and others.)

HEI-style on left, Ballast resistor style on right, with visible center electrode.

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HEI style has recessed center electrode, makes for longer spark gap.

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There are other styles of spark testers, including some with an adjustable gap. But I like these.

Example of HEI style:
www.amazon.com/dp/B003WZXAWK/?coliid=I3S98D7T1J0RLJ&colid=2VLYZKC3HBBDO&psc=1&ref_=list_c_wl_lv_ov_lig_dp_it