[george kujanski]

Yellow and red wires? red and white wires? pickup coil wire colors? on and on.......

Anyway, my GTO isn't running quite the way I want, so I connect my oscilloscope to the ignition. I notice some things in the waveform that look like it could be a misbehaving coil.

Several years ago I did an investigation regarding the chevy vs. Pontiac coil...you know, the above wire colors. i found that electrically there was no difference in the coil parameters between the two except the two coils had opposite magnetic poles, i.e. one was wound in the reverse direction of the other.

I still maintain that should have nothing to do with magic noise injection into the pickup coil, etc.

Back to today....I decided to change the coil, I had both from the previous investigation anyway, My HEI had the red/yellow wires.

I installed the coil with red/white wires. Guess what?





No observable change! The engine ran the same, scope display was the same, etc. I'll leave this coil in, just because.

On another note I bought an adjustable vacuum can, the Accel version. When I installed it I set it to about 14 degrees according to the instructions and it was about 20 crank degrees, down from 28 with the original can. Started adjusting it some more....now it went back to 28, probably it's maximum. WTF?

In another thread it was mentioned these are made poorly, the adjusting screw comes out, etc. I took it out, welded up the old one for about half of it's original travel, now it's at about 14 degrees.

Save your money.

Enuf for tonite...it still isn't running the way i think it should......

george

[MescaBug]

George,

I just experienced a weird problem with an HEI pickup coil. My HEI was acting funny, I disassemble the whole unit, added some new grease and felt washer, and a brand new pickup coil. The old PU coil had a broken wire (green).

White and green wires. Resistance checked out at 850.

I read some old threads where you, Schurkey and Suntuned talked about coil wires color and polarity and whatnot. Conclusion was that all pickup coils were basically the same, except the plastic connector color and wire length.

So I installed the rebuilt HEI, set the timing without vacuum advance. When I hooked up the vacuum adv to ported vacuum, a quick blip of the throttle almost stalled the car. I was like, wtf? A longer blip, and it stalled.

Seems like the vacuum was retarding instead of advancing, thus killing the engine. Remove the dist, repaired the old PU coil, put it back in, works like a charm. Tried the new PU coil once more, killed the engine.

My conclusion: I'm sure pickup coils do have a polarity. Is it possible that a reverse-wound PU coil (Chevy) in a Pontiac can in fact, works the opposite way? What's weird, is that Chevy PU coil have short wires, that cant reach the module in a Pontiac HEI....

I hope I am not jack-theading... But there seems to be quite a debate about coils and PU coils... I thought I'd share my findings. I asked Schurkey for his opinion, and I think he was baffled as well...

[george kujanski]

What kind of coil was the replacement? If it`s the same type, check if the connector is terminated the same way, i.e. the wires are not reversed.

George

[MescaBug]

Originally Posted by george kujanski

What kind of coil was the replacement? If it`s the same type, check if the connector is terminated the same way, i.e. the wires are not reversed.

George

Original Delco coil for HEI.

Looks exactly the same as any Pontiac HEI coils I've seen.

[george kujanski]

Normally the two wires are terminated in a plastic connector for proper polarization. Your pic shows individual terminals so there may be a chance they are backwards. I should have taken note on the connections when I had mine open yesterday. Bottom line is you need to make sure it's connected correctly first.

George

[Half-Inch Stud]

George,

My HEI crapped a 990 chip this Spring. 1st ever chip failure; it would act like fuel starvation when warmed-up and cruising. So I put another GM 990 HEI chip in, and it appears 100% even up to today.

Anyway: Back to topic; I was moved to ask if you noticed the pickup Magnet polarity between Chevy & PMD HEI to say that those are same? I'm thinking the pickup coils are wound different sense, like the HV coil. So I'm thinking the pickup coils are clocked different too for the application.

Pretty sure the HEI chip is looking for the same voltage sense regardless of application. so since I've seem white or yellow dots on the HEI chip package, I'm wondering why the GM chips would ever need matched to Pick coil & HV coil.

[george kujanski]

I haven't inspected the pickup coil to determine if they are wound differently, terminated differently, or both.

Technically tho, you are correct, I would expect the module to require the same signal to trigger, i.e. one module fits all. the pickup coil output will be the same regardless of the rotation, i.e. according to Lenz's Law..the voltage produced is proportional to : -(time rate of change of the magnetic field).

All that means is when the teeth approach each other, (from either direction), the mag field increases, the voltage produced by the pickup coil increases in one polarity, then the teeth are together for a split second, the voltage drops to zero since the field is not changing. As the teeth move away, the mag field decreases, the voltage then is produced with the opposite polarity.

When looking at the signal on a scope, there is a bunch of dead time and when the teeth line up, you get a positive spike, and then a negative spike, then more dead time, etc. The signal is very sharp to fire the the module at the right time.

So after the long winded explanation, I don't see why there should be more than one style of pickup coil. Rotation should not make a difference electrically. Mechanically maybe, since the arm for the vac advance needs to be on the opposite side in a opposite rotation distributor.

One of these days I'll look at the pickup more closely.

George

[Half-Inch Stud]

George, Correct echo on the pickup coil Voltage output vs magnetic gap in motion.

Pretty sure the 2 pickup coil types exist to appease the temporary magnetic field set by flipped starter stations. I remember reading GM info on that beyond folklore, but never got te magnet sense for PMD vs Chevy: my compass needle remagnetized and flipped its readings. (it happens to $1 china compasses). Regards, HIS

[TheSilverBuick]

I've gone back and forth with the coil types (Buick's use the same one as Pontiac) with zero noticable change in the running of the engine, MSD box or static on the radio.

I've asked on forums before for an engineering report, preferably a GM one, stating why the polorization matters and no one had one, or even a good electrical reason. It's windings in a secondary coil purely to collapse a magnetic field to generate the voltage for the spark, it just needs the magnetic field to collapse, doesn't matter which way.

And the pickup coil has no relation to the coil as it's signal is turned from a sin wave to a squarewave by the module, which the module part number is identical for both coil types.

[fiedlerh]

LAte to the party, but GM's HEI manual...

http://www.pontiacpower.org/HEI.pdf

[george kujanski]

Yep, read that before and still don't believe it. To believe battery cable and starter position makes a difference while a sparking rotor essentially right next to the ignition module is ok makes no engineering sense at all. The sparking and associated RF noise would be the predominant effect. The engineers have worked that out.

I'll need to be convinced and so far on a sample size of one, the two different HEI coil theory is false as far as i am concerned. A greater sample size would be needed... so far I've heard from a few others that HEI coils did not make a difference in their cars, and have not heard from anyone yet where it has.

Don't know where the original story came from, perhaps some well-meaning technician saw a strange effect during development, this became "the fix" (even tho it wasn't the cause), and once in production it was difficult or too costly to revert....I've seen it before......

I'm looking at it from a my fresh engineering perspective and so far (on a sample of one, granted) my theory = 1, published document from somewhere = 0.

Skeptical, need to be convinced. I'd love to see the lab notes taken during the HEI development. Until then.........

George

[johnta1]

Were the 74 'early' HEI/unitized wired the same as a chevy or like the later HEI?
Or even the earlier unitized distributors?

[george kujanski]

No clue.

George

[fiedlerh]

Were the 74 'early' HEI/unitized wired

74 HEI and 74 Unitized were two different things. There were 4 types of ignition systems available in 1974. Points, Uniset points, Unitized and HEI.
74 HEI was like other HEI distributors. Someday I'll have to do a side-by-side comparison.

George, GM's alleged observations seem strange. One would think why would an electrical field from a cable drawing 200 amps at 10 VDC affect an ignition system from a foot or more away? Especially when said ignition system is partially shielded by an aluminum housing but seeing 12kV spikes directly above the pickup coil and module. I believe one would have to grossly shift the zero crossover point of the pickup coil to trigger the module at the wrong time, or introduce additional false triggers into the module input.

Could the answer could lie in the dynamics of the starting sequence, perhaps in a worst-case scenario? Perhaps keying the ignition while various parts of the starting and or ignition system are in poor condition or poorly grounded?

[george kujanski]

Don't know, but I sure would like to know the back story of how this determination came about. I'm pretty sure it still exists today because any parts mfgr is not going out on a limb to refute the story, they make parts and sell parts, they don't develop ignition systems.

Here's a story...way back I took a course in value engineering, the concept is you analyze the various parts of a product in terms of function as a way to minimize costs, etc.

They told a story of a mfgr that made air brakes for railroad cars and were making them for decades. In analyzing the parts for a brake actuator, the bill of materials called for a single precision ball from a ball bearing placed loosely inside the actuator. When questioned, no one could explain the function.

After much investigation, way back they needed to correct a malfunction but also needed to distinguish between the modified one and the problematic actuator. They had some excess stock of these balls so they added one to each modified actuator and instructed the maintenance crew to replace the actuator if it didn't rattle.

So many years later they were still adding this precision ball to the actuator because the original reason was long forgotten, and no one questioned an existing, working design, and it was on the bill of materials.

True story....at least the way it was told to us in class. I suspect the same reasoning happened with the HEI....the reason for the two styles has long been forgotten and the paper lives on IMO.

HEIs are being replaced now with coil-on-plug, etc. so I'll never know.

George

[TheSilverBuick]

Originally Posted by fiedlerh

74 George, GM's alleged observations seem strange. One would think why would an electrical field from a cable drawing 200 amps at 10 VDC affect an ignition system from a foot or more away? Especially when said ignition system is partially shielded by an aluminum housing but seeing 12kV spikes directly above the pickup coil and module. I believe one would have to grossly shift the zero crossover point of the pickup coil to trigger the module at the wrong time, or introduce additional false triggers into the module input.

Could the answer could lie in the dynamics of the starting sequence, perhaps in a worst-case scenario? Perhaps keying the ignition while various parts of the starting and or ignition system are in poor condition or poorly grounded?

And for reference, the Buick engines used the same coil as the Pontiacs and the starters and distributors are on the opposite sides of the engine as the Pontiacs with the batteries located in the same place.

[68 Firebird]

When I had my HEI from a 76 TA a few years ago I questioned the same thing.
The unit worked well but had a chevy coil and Pontiac magnet pickup installed. Drove for
3 years and never an issue other than me changing springs to adj curve.

Well it was now tune up time and decided to install a new DUI HEI setup to my
cars specs along with new wires and plugs. When I spoke with them on the phone they said they used same pickup and coil for all HEI's (street/strip). Car starts better and is MUCH smoother at idle and less pedal for cruising. Have not tested WOT fully but
does pull better on primary side on rolling takeoff. So far I am very impressed with the
unit and service. Their live wires also fit well, just used wires based on length not how
were numbered(will remove numbers).

Gerry

[Ben M.]

Originally Posted by george kujanski

Don't know, but I sure would like to know the back story of how this determination came about.

I'm curious about this myself. It just doesn't make engineering sense why they would do it, despite all the armchair engineers telling me I'm stupid for not accepting it the way it is.

It wouldn't surprise me if it was something simple as a test or validation setup that ended up getting put into production due to lack of time or resources to standardize to one coil. Which in turn lead to the original team not documenting it fully because they got moved off to other projects, which in turn lead to "you must use this because the part number\book says so!" when in reality there is no engineering reason why the two are different. I experience this all the time at work since I run 50 year old high voltage machines for a living and maintain\upgrade them at the same time with little to no engineering documentation from the original sources.