Distributor ?'s - Chevelle Tech
Electrical & Wiring Troubleshooting electrical problems.

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post #1 of 56 (permalink) Old Jul 8th, 18, 11:41 AM Thread Starter
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Distributor ?'s

This must be my year for electrical gremlins! Last night took the Chevelle out for a ride...just going along and BOOM...quits. Flat-bed ride home. Finally got under the hood. Have an MSD Street Fire HEI-type distrib. Checked spark at a plug...weak and yellow...so I "think" it might be the coil. I know there has been much discussion about the epoxy-filled coils and how they "go away" so...what can I replace it with? Is there a in-cap type that is better and if so, where to get it. I really don't want to replace the entire distrib. if I don't need to. This is a street-only car with an occasional blast down the road. If more info is needed, I can supply it. TIA for your help!
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post #2 of 56 (permalink) Old Jul 8th, 18, 1:10 PM
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Re: Distributor ?'s

Before you go changing out parts check the voltage input at the positive (ignition) side of the coil. If it's less than 12v that is more than likely your problem.
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post #3 of 56 (permalink) Old Jul 8th, 18, 2:17 PM Thread Starter
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Re: Distributor ?'s

Will do.
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post #4 of 56 (permalink) Old Jul 8th, 18, 3:25 PM
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Re: Distributor ?'s

I'd do what was said first, check the volts with the key in run. Then, if it reads low, disconnect the BATT in wire, and jumper that terminal on the cap directly to the positive battery or alternator post, and see if it perks back up. Go from there.

As far as the coils, I suggest to use a stock HEI NAPA replacement, don't waste money on the same coil with a different sticker on the box.

An alternative would be to move the coil off the cap. There are coil cover adapters to move the coil off the cap, away from it. I have foound they work the best, over the in cap coils.

Also, if you have a good parts store with an off vehicle electrical component tester, might have both the coil and module tested. IF the in cap coil is faltering, the first result will be for it to compromise, and possibly "take out" not only itself, but the HEI module as well. Resistance readings are no longer that accurate, especially if the problem occurs when the coil gets to operating temps. Colder, they can read good as they are failing.
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post #5 of 56 (permalink) Old Jul 8th, 18, 4:05 PM Thread Starter
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Re: Distributor ?'s

Thank you, Dave! I was hoping you would see this and respond. My local NAPA store is close by if I end up needing it. Will try the other test(s) first. I have had this distrib. in the car for almost 5 yrs. and negver had an issue. I need to get it fixed up due to a big road trip coming up.
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post #6 of 56 (permalink) Old Jul 8th, 18, 8:24 PM
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Re: Distributor ?'s

Just info on what happens to the in cap HEI coils. They are epoxy filled, and epoxy is not a heat leaching compound, it is a heat rejection one. As we all know, coils produce heat internally, starting at the inner core, center of the windings. the center is where the most windings heat remains, and must be drawn away from, and out of the core, to the outer surfaces of the windings.

Since epoxy holds heat, the windings retain more resistance than they should, and overheating results. Eventually, the epoxy compromises, and cracks on its outer surfaces, and coil heat literally causes the insulation layers between the windings to disintegrate, allowing windings to touch, changing the heat production possibilities, and circuit resistances, over loading the coils to failure. This is called "layer shorting".

An added issue is usually that along the way of over heating, windings touching, and failure, the loading from coil to module increases, and causes module failure long before the coil finally gives up. Add to all this that the in cap coils have a coil cover, so even less cooling air flow travels across the coil, making things even worse.

Epoxy is usually used to make carb spacers that reflect manifold heat back into the manifold, away from the carb, reject heat away from something.

Oil as a cooling media in coils works very close to what an old car had, with a liquid cooling system and no water pump, called "Thermo-Siphon". The heat production media heats up the oil in contact with it, the oil rises to the top of its pool, and outward in a canister, to the inside of the outer jacket, begins to fall down the pool wall, cooling as it flows, then at the bottom of the pool, is drawn back into the heat source, to cool all over again, thermo siphon.

I've taken coil covers off a lot of wrecking yard HEI's, still in their cars, and found more than I'd like to see of cracks in the in cap HEI coils. Those coils finally got so hot, they cracked their epoxy bodies, and failed. The key give away is to look at the car, no accidents, no dents, the coil is cracked, and the car was junked because it stopped in its tracks for its very last time, owner done with it, wrecking yard.

That is why I always suggest one of the MSD, or before, Mallory large HEI coil change over caps, which allow for a remote coil, mounted off the cap. I go with a round oil filled coil then, coil, and usually, HEI module failures stop.

Just info to consider.
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post #7 of 56 (permalink) Old Jul 8th, 18, 9:06 PM Thread Starter
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Re: Distributor ?'s

Isn't it interesting how the advertising hype favors epoxy-filled coils..."..to withstand racing conditions." or "...epoxy-filled for better heat and vibration resistance"...why? Must be cheaper and more profitable for the makers.
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post #8 of 56 (permalink) Old Jul 9th, 18, 5:42 AM
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Re: Distributor ?'s

Duke,
Epoxy IS better than oil for heat dissipation & vibration resistance. Epoxy has 2-3 times the thermal conductivity of transformer oil.
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post #9 of 56 (permalink) Old Jul 9th, 18, 9:59 AM
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Re: Distributor ?'s

This has been gone over time and time again, there is only ONE epoxy that is heat leaching, and it was only used on our Space Shuttles, never in auto ignition coils, as it was just a small bit too expensive, only 100K dollars per OUNCE.

Please list all heat leaching epoxies, so we can all search for ourselves, for the FACTS on those listed.

DO NOT JUST COPY AND PASTE.
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post #10 of 56 (permalink) Old Jul 9th, 18, 1:35 PM Thread Starter
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Re: Distributor ?'s

OK, have 12V+ at the input wire for coil,,,same as the battery voltage. Took off coil and it "looks" fine...almost like new but of course I have no idea wht's going on inside. This coil has about 5k miles on it (as does entire engine). Should I bother testing it and the module or just go ahead and replace both. Don't need any breakdowns when I go to Ohio in Aug.
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post #11 of 56 (permalink) Old Jul 9th, 18, 7:20 PM
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Re: Distributor ?'s

Duke, Please have them tested, never learn anything just by throwing parts at a situation. Please also do the jumper wire from BATT positive terminal to BATT on cap, and see if it gets better, if not, then, parts store, run test there.

Still waiting for the epoxy info, any time now.
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post #12 of 56 (permalink) Old Jul 9th, 18, 7:26 PM
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Re: Distributor ?'s

Quote:
Originally Posted by Dave Ray View Post

Still waiting for the epoxy info, any time now.

With your tongue planted firmly in cheek, no doubt.

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post #13 of 56 (permalink) Old Jul 9th, 18, 7:45 PM
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Cool Re: Distributor ?'s

Do parts stores really still have the equipment and knowledge to test coils and modules? Some of the counter help Iíve dealt with can barely cash you out without incident.
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post #14 of 56 (permalink) Old Jul 9th, 18, 8:49 PM
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Wink Re: Distributor ?'s

Amen
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post #15 of 56 (permalink) Old Jul 9th, 18, 9:08 PM Thread Starter
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Re: Distributor ?'s

Quote:
Originally Posted by Dave Ray View Post
Duke, Please have them tested, never learn anything just by throwing parts at a situation. Please also do the jumper wire from BATT positive terminal to BATT on cap, and see if it gets better, if not, then, parts store, run test there.

Still waiting for the epoxy info, any time now.
Will check with my local NAPA tomorrow and see if they can check both. Will also tyr the direct wire test and get back to you. Agree that just throwing parts is foolish...BTDT before. Expensive and dumb!
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