testing HEI coil

al daniels

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the pickup coils in these had a problem with the wires breaking inside the insulation due to the movement of the advance mechanism.connect an ohmeter to the two wires coming off of the pickup.cant quite remember the specs,i think 3000 to 5000 ohms.doesnt really matter because either you get a reading or not.also wiggle the wires while you take the reading.any fluctuation or no reading indicates a broken wire.this is the next most common failure after the mod.
 

NickD

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Probably the same unit in my 82 454 engine, was centrifugal and vacuum advance as opposed to the electronic spark controlled unit used in later model years that lack these mechanical components.

Here is the circuit and a refresh of my memory.



Just a three transistor circuit. The base of TR3 is grounded through the trigger coil and that transistor will be normally in the off state. TR2 is normally on, and TRI is normally off. Dwell is determined strictly by the trigger coil. Trigger coil generates a negative pulse that reverse biases D1 causing TR3 to switch on as well as TR1 to allow current flow in the coil primary circuit. Just shorting the two trigger terminals together in tapping method would do the same as the pulse. Instead of a coil for the load, a 20 ohm 5 watt resistor could be used to check if the collector voltage is also pulsing with a voltmeter attached to the collector pin, to assure the module is switching.

R1 is the current limiting resistor for TR3, that capacitor is just a B+ filter, not showing the zener diode from the collector of TR1 to ground, but I know its there. Collector of TR1 is also the not shown tach terminal.

Just enough to replace the points.
 

mhamilton

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Thanks Nick! Haven't been able to find a full schematic. I will definitly save that one!

Al, I agree, though I've checked the pickup coil as well. It's got to the module or coil, I'm leaning toward a bad module. But I will check thoroughly.

Here's another question: when you connect a tach to the HEI, does the other end of the tach go to ground or 12V? Or is the tach a 3 wire setup with its own positive and negative, and just a signal from the HEI tach wire? The tach in this car works, but I did not wire it and have no idea what was done. And with the previous coil failure, I'm wondering if that could be causing an issue here. BUT--for all these tests I've done the tach wire was disconnected and left aside, so it is not involved with this no-spark problem.
 

NickD

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Had a whole box full of HEI parts, was shortly after my accident that my loving wife decided to divorce me. Had a court order to sell my home and was forced to clean it up. When this thread popped up on the HEI, looked for that box. Must of pitched it along with a bunch of other stuff. It was all brand new stuff, just wondered how you got your collection.

Ha, had to buy new bushings for my last HEI job, that almost killed me. Was surprised to find this circuit diagram, pitched over two hundred feet of automotive books and literature.
 

mhamilton

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NickD said:
Must of pitched it along with a bunch of other stuff. It was all brand new stuff, just wondered how you got your collection. Ha, had to buy new bushings for my last HEI job, that almost killed me. Was surprised to find this circuit diagram, pitched over two hundred feet of automotive books and literature.
I'm actually not sure why there were so many HEI coils in the garage... I know two were from spare HEI units I had. The other 3? One was out of the car in question, the other two I'm not sure lol. Know what you mean about saving literature... one of my favorite references is a 1986 Chilton's for American cars. Covers basics of all the big 3 models from 76-86, plus generic info on ignition, ac, brakes, emission controls, etc.

Maybe this weekend I will find out if the module or coil is the problem, and sort out those other coils in the working car to find out which work! I will post back.
 

mhamilton

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fixed

It was the module, the brand new module that was just installed. Got another new module, the engine started on the first click.

I knew you could get a bad module out of the box, but nobody has module testers in the stores anymore! Anyway, going to wrap this up and hopefully it won't have any more issues. Thanks again to everyone for the help!
 

Broc Luno

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OK, I know this an old thread, but I'm just now going through my pile of old HEI's, and sorting them out. Since these are pre-ECM ignitions, and mostly from the 1970's, they are now antiques. I guess I am too ... I've been building HEI's for friends for years. Took a long time to learn the idiosyncrasies of the type. So please, if I mis-state something, jump in and correct.

Note, I do not work on 7-pin module units that interface with ECM's as they are a science all their own.

OK, lesson number 1: It's the coil. Does not matter if it's a Ford Dura-Spark or a GM HEI, the coil is the common failure point. These are all epoxy potted E Coils. They have poor thermal conductivity. Ford's at least are out in the open. GM's are in in the back of the engine with poor air circulation and under a "Coil Cover" that helps trap the heat. What happens is they get hot and short internally. That short takes out the module. Often when they cool down, they will start and run again, for a while ... So, if you have a bad module, please replace the coil first. I have found that ProForm coils are pretty reliable. More so than OEM Delco coils if you are hitting them with increased plug gaps.

Lesson number 2: It's the ground. Almost all of these distributors ground through the body and the hold-down clamp to the manifold and engine block. This is iffy at best. There is a fiber gasket under the distributor flange. The hold-down clamp may be painted, or plated, or corroded. It may not make good contact ...

So all the HEI's I build have the condenser (capacitor) hold down screw extended out the bottom of the unit. A separate ground wire with crimped and soldered terminals is run from under a nut on this "stud" (the extended screw) on the bottom of distributor body to a bolt pad on the intake where the old round coil mount used to attach. Almost all GM and aftermarket manifolds still have these bolt bosses on top of the back of the manifold. Handy, close and they easy to reach. Corrosion, grease, dirt, and salt make any connection into a semi-conductor. It will give a false voltage reference and restrict current flow. Neither is good, so do the dedicated ground and the ignition will almost certainly improve.

Lesson number 3: Clean is good. If you look under cap of most HEI's you'll see rusty advance weights. And if you look under the rotor, you'll see a film of brown rust powder everywhere. Look closely at the cap and you'll see a fine film of brown too. This dust film is partially conductive. It's responsible for most of the flash over going to the wrong places.

The solution is to clean everything. Small parts brushes and 409 or other good household cleaners will get it off the plastic parts. No need to replace the cap and rotor 99% of the time. Just clean it real well. Top, bottom, inside, outside - everywhere. Then use some DOW high temp grease sparingly applied to the terminals when you reassemble. It'll keep the moisture at bay and slow the next round of rust. You can wipe thin film on the advance weights (hardened blue steel that likes to rust) to slow it down there. If you install a Moroso advance kit to recurve the distributor (good idea), make sure you wipe a thin film of high temp grease on the blued steel parts too.

Lesson number 4: Oil is good. I don't know how many distributors I have taken apart in my life? Prolly over a 100, and I'm just a hobbyist. Almost all had defective advance systems, broken springs, worn out swing pivots, and the like. Many would not advance at all - stuck. And you wonder where your gas mileage went ??? HEI's run a long time, even in bad shape. At least back in the points days, you had to get a tune-up now and then. And if the mechanic was worth a hoot, they would lube stuff, even if they did not clean it ...

About every 25,000 miles, you should pull the distributor out, knock it apart, clean everything, lube it all and reassemble. About 2 hours work all up. You'll be amazed at what you find. Frozen mechanical and very sluggish vacuum advances are common. You'll need a 2x4 cut into a Vee Block with a drilled opening in the vee at one end to drive out the roll pin from the gear that rides the cam. Once that gear is off, the main shaft slides out the top. If it feels like it's binding part way up, it's just baked on oil and condensation goo. Brake Clean up the housing leg and some elbow grease will get it out.

Now you can see if the vacuum advance is working? Couple of drops of oil in the cup around the main shaft bearing will help. Look over the body and make sure no wires are rubbing. I suggest popping the "Module" out and looking at the bottom. I'll bet there is a small patch of dried out high temp compound in the center. Not nearly enough. Clean it all and get some high temp heat past. Spread a thin layer over the metal base of the whole module. Remount on the pad and make sure you have a bit of "squeeze out" around the edges. OK, now you have some reasonable heat transfer. Is it any wonder modules burn out? They can't shed the heat with poor contact and dry surfaces ...

Now hold the main shaft upside down and oil the bottom of the advance shaft/collar. Move it back and forth until you can feel the new oil loosening and smoothing things out. Now flip it over and put a few drops between the "plates" and a drop on each pivot point. If the plastic pivot bushings are shot (very likely), you'll need a Moroso advance kit. There are no more GM/Delco plastic bushings to be had. The Moroso kit comes with new bushings that fit their weights. They are not interchangeable.

OK, now reassemble, re-install, and re-time your motor. All good to go :)
 
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NickD

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Since I received my first HEI from Delco, (history), they had to supply to GM for $6.00 that included the entire complete distributor and eight silicone spark plug wire with connectors. But forget the six bucks, paper work costs more than that.

GM dealer wanted 150 bucks just for the base distributor, excluding the cap, coil, and spark plug wires.

Had some minor problems, gals soldering the trigger coil had cold soldering joints. other was lack of lubrication for the upper shaft bushing. Filling that with Wolf's Red high temperature bearing grease cured that. Carbon tip on the rotor would break off.

Did have manual centrifugal and vacuum spark advance. Easiest car to steal just apply 12 vots to the distributor terminal, starter solenoid could be jumpered.

Dumbest thing was suggesting gaping the plugs at 63 mils, spark would blow out, ran so much better gaped at 25 mils.

Mechanical distributors were replaced by distributorless (what a name), my last design was about 9 years ago before my company moved to China, I stayed here. For an eight cylinder vehicle had to be manufactured for also $6.00, but from 1972 to 2011 a buck was only worth about 11 cents. So somethings don't change. Sticker prices sure did, skyrocketed.
 

Broc Luno

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All good. There are still many HEI's in use on older trucks that get run occasionally and a lot of boats. In both cases, the goo of time, plus corrosion from sitting are killing these ignitions.

To replace one with a complete MSD Pro-Billet distributor and a 6AL box will cost upward of $500. Not practical. Just go through your exsiting HEI and make it work as it should. Mileage and power will return and you save a ton of money :)
 
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