Hello all,

I have a ol truck that I use to haul stuff, and I keep having to replace the coil in the HEI. This truck is currenlty using the 3 wire module, has newer plugs and wires.

After I replace the coil, the truck will run great for some period of time. At some point, I will go out to the truck to drive it or move it, and then it won't hit a lick. Change the coil, and away we go.

Module bad? Something else? I have used up all my good coils, now I gotta start buying parts :mad:

Sure would appreciate any help out there!

Thanks, jer.

I would start with the module. My brother worked at O'Reillys Auto parts and he sold lots of them. It is usually the first thing to go in an HEI. If that doesn't fix the problem, check ebay. There are prenty of complete HEIs for less than $50.00. Good luck!
Rick

Did you ohm-out the bad coils? I would wonder if they were really bad. Maybe you have a bad connection and that R&Ring the coil moves something that gets it working again for a while. Just a thought.

Did you ohm-out the bad coils? I would wonder if they were really bad. Maybe you have a bad connection and that R&Ring the coil moves something that gets it working again for a while. Just a thought.
funny you mention that - I have a Crapsman digital ohm meter that has worked quite well in the past, but it appears the terminals are dirty or something, as it's operation is erratic at best. Tried to fix that, but seemed to be a losing battle. So, I wasn't able to do any testing on the coil(s).

I've got a stack of bad parts that I can't prove is bad ;)

I'll try to dig a bit into it and see what I can find out.

I think a new module should go in with the next victim, I mean coil.

I would start with the module. My brother worked at O'Reillys Auto parts and he sold lots of them. It is usually the first thing to go in an HEI. If that doesn't fix the problem, check ebay. There are prenty of complete HEIs for less than $50.00. Good luck!
Rick

I'll try a module, thanks

From Dave Ray (IgnitionMan), he reads this, and other sites, and then, asks me to post responses for him, when he feels he might be of help.

"Please post this on the Team Camaro board, for hotrodf1.

HEI modules more so than not, ARE NOT usually the cause of HEI coil failures, just the opposite, coils fail modules. HEI in cap coils are epoxy filled, and do not leach heat created in their cores outward, they hold the heat in the center of the coil, and fail. The overheating causes the windings insulation to fail (called layer shorting), and when the wiring touches together inside the coil, the resistance and load gets exponentially greater, overloading the coil, and most times, module to failure.

There are a number of areas to look if coil failure, and subsequent module failure continues. System voltage, test at full operating temperature, 2,500 rpms, ad the distributor BATT terminal. 14.40 to 14.60 volts is fine, lower won't hurt, unless it gets down around 10 volts or so, and then, the HEI will just fail to work, Too high, coils will overheat and fail. HEI coils have a grounding bar under them, goes from the coil yoke to the center terminal of the 3 wire connector, and to distributor ground. Dirty, increased resistance, failure, or, no contact, coil won't fire. Older rotors were made form lower quality plastics and can transmit spark through them, increasing resistance and heat, failure. The carbon brush under the coil is also a place problems can start. The order it is installed is, cap, brush with spring, insulator donut, coil. Some put the carbon brush in after the insulator, placing the brush off and upwards of the rotor bar, making for serious increased resistance, heat, and coil/module failure.

Testing the HEI coil used to be OK with only an ohm meter, but not today. Load testing the coil off the distributor, on a machine designed to do so, IS the right, and only way to test them. If the module is bad, then I would seriously think the coil(s) were responsible for the module going out.

Whenever I do a large cap HEI, I ALWAYS remove the coil in cap coil, and install a remote, round oil filled coil, just saves a lot of problems from that heating device on the top of the distributor jokingly referred to as a coil. This removes a lot of under cap temperature, and usually, stops the coil/module failures in their tracks.

I just saw a situation I have never seen before in an HEI module, it would drive the scope in my distributor machine fine, made excellent pattern, but wouldn't drive the coil to make a spark. I have not seen that happen before, partially failed module."

Dave, and I, hope this helps fix the problem.

Regards,

Milton

Milton (and David) thanks for the refresher and update! I have been out of the daily grind of being a mechanic for 20 years and out of auto parts for 15. I had forgotten about the ground strap in the middle terminal and the grief it can cause when missing.

Jeff

From my memory, the large cap HEI's need that ground strap to run, they won't run at all unless it is in place, and not compromised by dirt/corrosion. This is unlike a remote coil that doesn't need to be grounded. I remember that the in cap coils also have a ground strap that goes to another one of the coil hold down screws in the cap.

So, the coil grounds to its own yoke, then, from the yoke to the center terminal of the 3 wire connector via the buss bar under it, then, down to the screw that holds the wiring loom and noise suppressor in the distributor body.

At least, that is the way I have seen on every coil in cap HEI. In cap coils are the only ones I have ever seen that need to be grounded to make spark.

Dave will know more about this, and if so, I'll hear from him on it and post if so.

Regards,

Milton

Make sure you have a ground strap running from the engine to the firewall and one from the engine to the frame. The lack of a ground strap will cause the coils to burn out in short time.

The engine is the ground for the module and coil, and, the engine should have a direct negative large gage wire, called a battery ground wire, directly to the negative post on the battery, so, no extra ground straps should be needed. The coil ground path should already be from coil to distributor body to engine to negative battery cable to battery negative post, no diversions form that path.

Regards,

Milton

The distributor is grounded through the dist clamp and the gear drive. There is a gasket between the bdy and intake to seal oil leakage.

An extra ground strap from the dist body to ground may not be a bad idea.

From Dave Ray (IgnitionMan), he reads this, and other sites, and then, asks me to post responses for him, when he feels he might be of help.

"Please post this on the Team Camaro board, for hotrodf1.

HEI modules more so than not, ARE NOT usually the cause of HEI coil failures, just the opposite, coils fail modules. HEI in cap coils are epoxy filled, and do not leach heat created in their cores outward, they hold the heat in the center of the coil, and fail. The overheating causes the windings insulation to fail (called layer shorting), and when the wiring touches together inside the coil, the resistance and load gets exponentially greater, overloading the coil, and most times, module to failure.

There are a number of areas to look if coil failure, and subsequent module failure continues. System voltage, test at full operating temperature, 2,500 rpms, ad the distributor BATT terminal. 14.40 to 14.60 volts is fine, lower won't hurt, unless it gets down around 10 volts or so, and then, the HEI will just fail to work, Too high, coils will overheat and fail. HEI coils have a grounding bar under them, goes from the coil yoke to the center terminal of the 3 wire connector, and to distributor ground. Dirty, increased resistance, failure, or, no contact, coil won't fire. Older rotors were made form lower quality plastics and can transmit spark through them, increasing resistance and heat, failure. The carbon brush under the coil is also a place problems can start. The order it is installed is, cap, brush with spring, insulator donut, coil. Some put the carbon brush in after the insulator, placing the brush off and upwards of the rotor bar, making for serious increased resistance, heat, and coil/module failure.

Testing the HEI coil used to be OK with only an ohm meter, but not today. Load testing the coil off the distributor, on a machine designed to do so, IS the right, and only way to test them. If the module is bad, then I would seriously think the coil(s) were responsible for the module going out.

Whenever I do a large cap HEI, I ALWAYS remove the coil in cap coil, and install a remote, round oil filled coil, just saves a lot of problems from that heating device on the top of the distributor jokingly referred to as a coil. This removes a lot of under cap temperature, and usually, stops the coil/module failures in their tracks.

I just saw a situation I have never seen before in an HEI module, it would drive the scope in my distributor machine fine, made excellent pattern, but wouldn't drive the coil to make a spark. I have not seen that happen before, partially failed module."

Dave, and I, hope this helps fix the problem.

Regards,

Milton
Great Info. It's on a 68 Mustang, a 351W with some serious compression but the coils and voltage are fine while cranking. My coil failure happen when the ignition is left on for a few (1-3) minutes without starting the car. Almost always kills the HEI coil. I know - don't do that. But it happens while we are restoring/tuning the car. I think it's tied to voltage drops, possibly (10-11 volts) and heat buildup inside the coil. I'm trying to think of a better way to control the HEI input always making sure you have a solid 12-15 volts with plenty of current. Anyone made a setup like this work? Relays, Diodes, other ideas?

HEI coils have a grounding bar under them, goes from the coil yoke to the center terminal of the 3 wire connector, and to distributor ground.

Many people go to their local parts store and buy new cap, rotor, wires, module and coil and replace the whole works all at once. If they do not disassemble their old set-up, they won't even know the stamped steel grounding strap is inside and attached to the coil frame. I sold parts for many years and have seen many coils burned out from not having the ground strap in place. Standard Ignition, or maybe it was Neihoff, put out a bulletin years ago about this problem. The car will start and run without that ground strap as the coil will ground some other way. It just won't run as long as it would with the correct ground. I'm sure there are many other possibilitys also, that's just the first one I would look for.