1970s HEI modules from the 70's and 80's

[Cadman-iac]

I've been wondering about whether it's possible to use a 5 pin module from a 6 cylinder Chevrolet in another HEI distributor in order to retard the timing when it's knocking, or rather to prevent it from happening in the first place.
As I've been going through my distributors, I noticed that I have 2 with a 5 pin module. The one I know what it came out of is a 1981 El Camino with the 229 V6. Obviously a computer controlled engine, but it also has a vacuum advance on it. There's a vacuum switch on the manifold that grounds a circuit to the module that retards the timing any time the vacuum drops below about 9 or 10 inches.
I've got to study the service manual for this system, but it looks fairly straightforward from what I can see.
Does anyone know about these modules?
The distributor has the usual connection for the coil, but also has a single wire coming out of the location where normally you would see the ECM connection.
I know that the vacuum switch is set at that from testing it years ago, as I had considered using it for something else.
I hadn't looked into why it was on the car until I pulled the distributor for parts, and that's when the light bulb came on.
One thing that is not clear to me right now is that the pickup coil/magnet and assembly, although it's got 6 points on it, it has an odd configuration to it.
I'll have to get some pictures to post a bit later today.
But is anyone familiar with this setup?

Rick

[TJ Hopland]

The coils have to have the right amount of points on them since that's what is the trigger.  Differences other than number of cylinders was if it was for vacuum or computer controls.  Vac was set up to pivot and had the arm for the vacuum can to attach to.   The computer ones just had a mounting bracket sort of thing.  Other difference was rotation so the polarity was different.   Wire colors was how you knew if it was a reverse one,  Olds I think was one that was the other direction.  White vs yellow wire maybe?  I don't recall anymore. 

Those 5 pins which being mostly a one year thing are pretty hard to come by and I think it was just one year because they just were not that useful.  You allready have the vacuum control so another vacuum control is goona be a pretty narrow use case where it does anything.

What I saw is over time the vacuum cans even if they claimed to be direct replacements tended to get more and more range in em so you tended to get detonation at cruise so people roll back the whole works and kill the pep when likely all they needed to do is limit the travel of the vacuum.   

[Dave CLC#16900]

I don't recall the number of pins (5?) but I did buy some HEI modules with an extra pin that retards timing.  They come in different amounts of retard, somewhere between 5 and 10 degrees. 

I installed one a few years ago in my '75 Coupe with a small performance cam to retard timing during crank.  This let me bump initial advance to 16 degrees and crank at ~10 as I recall.

[Cadman-iac]

 Yeah, I got all that figured out. The piece with the starwheel,  or reluctor on it can be swapped with one from a V8, and the module doesn't know the difference. It only registers the signal each time the tips pass each other. The pickup coil magnet and trigger, or pole piece is swapped at the same time as the rotating piece.
 I dug through the 81 service manual and found the information on the 5 pin module and related stuff. Apparently the ECM has nothing to do with this part, as far as I can see. There is a tachometer signal conditioner that I don't understand what it actually does. It was mounted between the relays for the air pump valve and another that I can't remember its purpose. On a V8 car, the map sensor would sit there.
 The distributor housing has an extra slot on top for the 5th wire to pass through, but it's a smaller slot than the one for the ECM 4 wire connection. If someone wanted to, you could make a slot for this. But since I have the whole distributor, I'm thinking about trying it out on my Suburban to see if it would work for a V8.
 I can check the timing when the 5th wire is grounded to see how much it retards. It may not be worth the bother, but I won't know until I try.
 If it works, I can fine tune it with an adjustable vacuum switch, like maybe what they used on the Deville's in the late 70's. My 77 has one that turns on a light to indicate too many toes in the carburetor, and I've got another from a 78 I parted out.

 These are the pickup coils for both a V6 and V8. Note the odd configuration of the V6 pole piece. Every other one is larger.


 The various modules used in the HEI distributors. These are the ones I'm not currently using, thus the lack of multiple 4 pin modules.


 The harness on the left is for a fully computer controlled engine, the one on the right is the 5th wire on the 5 wire module that goes to a vacuum switch that grounds it at 10"Hg.


 The vacuum switch used with this system.


 The schematic for the 5 pin system.



 What little bit of literature I could find on this system.



 This is what they are calling a tachometer signal conditioner. After opening it, you can see they didn't want anyone to figure out how it works by covering it in silicone.


 A Cadillac vacuum switch from a 78 for the economy lights on the dash. If I can get the 5 pin system to work, I can possibly use a switch like this to adjust when the timing retard occurs.

 What started out as a simple search for HEI distributor advance parts has morphed into all this.
 What made me think about this setup is the question I posed on using a knock sensor to turn on a light or to somehow retard the timing without having to use an ECM. That isn't possible, but this 5 pin setup just might be.
 I'll post my results when I get done with it.

 Rick

[Cadman-iac]

I don't recall the number of pins (5?) but I did buy some HEI modules with an extra pin that retards timing.  They come in different amounts of retard, somewhere between 5 and 10 degrees. 

I installed one a few years ago in my '75 Coupe with a small performance cam to retard timing during crank.  This let me bump initial advance to 16 degrees and crank at ~10 as I recall.

That's very interesting Dave. I would think it would have to be a 5 pin module, as the normal 4 pin has no method of retarding the timing.
How did you work that, tie the 5th wire to a ground circuit on the ignition switch?
And what did you have to do to get the wire through the housing, cut an extra slot for it?
 And where did you find those?

Rick

[Suntuned]

  TJ Hopland  You are correct about the accuracy of the available vacuum advance units you can have two of the same number and one advance would start @ 8" and the next one @11" one may have 14 degrees advance and the other one 12 degrees they are not always real accurate now days. that's why you have to test and then limit the vacuum advance if necessary. There are eight data point specs given  for most stock Cadillac  vacuum advance units and  it  is different depending on the distributor model # & year . The original Delco units are the most accurate, they fall within the called for spec for example start @ 8-10" end @ 14.75-16.75 with 10 degs advance they will be within that parameter. 

[TJ Hopland]

I have had them that could pull close to 30 degrees if you let em.  I can't imagine any application that would want that much in in vacuum.  More typical is around 20 but when most of the specs are in the lower teens its still too much and will mess things up.

[Cadman-iac]

TJ 

Most of the vacuum advance units I've got have between 16-20 degrees in them, but of the 3 Cadillac units, one is missing the vacuum unit, however the other 2 have 28 degrees of advance. That's a lot in my opinion.

Rick

[Cadman-iac]

  Dave,
 I took a closer look at the two 5 pin modules I've got. I had thought they were the same, but after reading your post I started wondering about it.
 Seems I've got two different ones, and if you look closely at the picture I posted earlier you can see the difference in the 3 pins on one side.
 So I know which one came from my 81 El Camino, it has 3 different sized terminals, and the 5th wire connector only fits the smallest one.
 The other module has 3 evenly sized terminals on the one side, and has different letters labeling them.
 Now I'm trying to remember what I took the other one out of.
 I did some more research on the web on these, it seems that this idea does work. But the retard feature is apparently activated differently between them. The one I took from the El Camino uses a ground to retard the timing.
 The other one I'm not sure yet, but I think you have to apply 12 volts to the 5th pin to retard the timing. Gotta keep looking into this to be sure, and I don't know yet how much either one will retard the timing.
 
 It's funny, I was just trying to figure out the centrifugal advance curve variations on these and stumbled upon a way to retard the timing without a computer.

 Now I have to ask you, when you put one in your 76 Cadillac, you didn't have to change anything else to make it work did you?
 The reason I ask is I was looking at the second module and I believe I have the harness that was connected to it, and  possibly the distributor housing as well. I had thought it used the same housing as the 81 El Camino, which has a vacuum advance unit on it, and the extra slot for the 5th wire.
 Looking through all my distributor housings, I don't have another one that matches the 81, so I am wondering if those with the other design 5 pin modules did not have a vacuum advance, but used an ECM instead, and has the bigger slot for the wiring to the ECM.
 Another reason is because of how the pole piece is shaped on the 81 with the module that has 3 different sized terminals.
 It would be nice to find out this stuff before I attempt to use it, but I'll end up trying it anyway. I just would like to know before I accidentally let the magic smoke out of something if that makes sense.
 Thanks for any help you can provide.

 Rick

[bcroe]

The direction of rotation of an HEI does not affect the
polarity of the pickup coil output. 

I read there are different versions of the 5 pin module. 
An early one used in 79 Cad 350 Olds engines outputs
the pickup coil signal to an electronic module.  This
module then can then delay feeding the signal back to
the HEI module varying amounts, for starting, normal,
or light load cruising. 

The module with 5 pins on one end was used in the CCC
systems for a totally computer controled spark advance. 
Also worked with some add on systems.  Might be the
way to go for anything fancy, just lock the mechanical
advance parts in a good position.  The rotor tip should
partly overlap the plug stud for any advance number used. 
Bruce Roe

[Cadman-iac]

  Bruce,
 The thing with this distributor I pulled from the 81 El Camino is that it has both the centrifugal advance and the vacuum advance on it.
 Looking at the service manual it shows the same setup, and the 5th wire goes directly to the vacuum switch for grounding when it hits the parameters.
 I have read and noticed, that the HEI coils have 2 different wire colors depending on what it was used on.  The Olds Toronado uses the same one as the Cadillac and Chevrolet, with red and yellow wires, but all other Oldsmobiles and Pontiacs use one with red and white wires. Apparently, the pickup coil is matched with the coil, but I haven't found anything that explains the difference. I suspect it's in the direction the pickup coil is wound because the distributor rotation is CCW on the Olds and Pontiac. It must make a difference in the signal, that's the only thing I can think of for the difference.
 I have both ignition coil types, but not the pickup coils, I just have the ones with the yellow and white wires. I can't remember if they all have the same wire colors and just the connector housing is a different color, or if the wires were as well.
 If it's just the connector housing, is there a way to tell if it's a Cadillac or an Oldsmobile pickup coil?

 I finally remembered that I parted out a 1980 Cutlass Cruiser A body wagon some 30 years ago, and I kept the parts from
the distributor from the 260 V8. So I may have an Oldsmobile pickup coil in my collection. The problem is that I've needed the connector housing for some of these other distributors if the connector was broken or brittle, and I wasn't aware back then that there were different colors for different vehicles, and I used what I needed to.
 
 What started as a simple task has turned into an interesting education for sure.

 Thanks for your input, Rick

[bcroe]

As I said reversing an HEI rotation WILL NOT reverse
the pickup coil output signal, so there is no reason
to reverse wind the coil. 

My observation is  all pickup coils are the same,
though they may be wired into varied circuits.  I do
not believe the varied output coil wiring colors
have any influence on the pickup coil used.   

I have seen a couple explanations on why
different output coils were used, none that
satisfied me.  But I have not made measurements
on them yet. 

Starting in the 80s with computer engine control,
there were a few different HEI module variations. 
The only one I have seen fully explained is the
CCC version.  Bruce Roe

[Cadman-iac]

  You know the saying "You don't understand everything you know about this" applies to me here, lol. I didn't think about the direction of rotation as being the same as reverse winding the pickup coil, but after your explanation it makes sense now.

 I mis-typed earlier when I said I had pickup coils with yellow and white wires, they're yellow and green.

 Yeah, the 7 pin units are fully computer controlled, which is what I've been trying to get away from. I've been running one since 1989, so I'm familiar with them.
 I'm not wild about using the module in an HEI, but it's kinda gotta go together or you're back to points.
 My reasoning is that if it's mechanical it can be fixed if it breaks, but more often than not an electronic part is toast once it quits working.
 In the case of the HEI, a spare module doesn't take much space, it'll fit in the glove box.

 I did find a video where the guy shows how to wire the various modules and how they work.
 I didn't know that they all will work like the 4 pin modules in a pinch, you just have to use the right size terminals to connect it with. I'm not sure how long you'd want to try running one like that, but I know now that if I had to I could in a pinch.

 The guy said something about the 5 pin module with different sized pins being used in an Olds, but I think he got the two confused. I know for a fact that the one that has 3 different sizes is the Chevrolet one, I just last week pulled it out of the car.
 The one with 3 evenly sized terminals is the one I removed from the Oldsmobile years ago. At the time I didn't know anything about that particular module and system, I think I scrapped some of the pieces needed to make it work with the rest of the vehicle.

 I did want to ask, why did they use the igniton coil with the red and white wires, instead of just using the same one Chevrolet did?
 Is there something different about them other than the color of the wires?

 Rick
 

[TJ Hopland]

I guess I didn't think about the rotation and polarity thing and it makes sense that the rotation would not matter.   I know from experience if the polarity is wrong you end up with the 'fire' happening really sloppily somewhere between the points vs fairly sharply on them.   So if the coil was different you would need the module to be different to match again.

Is the Toronado thing a clue?  Only thing I can think of that would be different about a toro is doesn't Olds usually have the starter on the drivers side? But in toro its on the pass side because the trans ends up in the way?   But what the heck would that have to do with the pickup coil?


I think the '5 pin' module is one of those flawed terms like trying to identify all rear ends by the number of bolts.  I'm thinking I remember the turbo Buicks had their own 5 pin variant that was tied to a knock sensor, possibly first use of such a thing?   I will have to think about where my distributor box may be, I do remember having both a turbo buick and pontiac in there.  Was one of those things I saw at the u pull junkyard 30+ years ago and figured I would need someday......  Somewhere I have a box of modules and weights and springs too, another thing I just got at the junkyard when I saw them. 

Will have to think about where those may be because now I'm curious if I have anything unique.  I do remember experimenting with some of them on a 2 stroke golf cart.  Those you reverse the engine to reverse so you could not have an mechanical advance so I was trying to see if I could do it cheap with electronics. All I can remember about that project is I never got it past twisting wires together for proof of concept.  I had kinda forgot about that till this thread.   

[bcroe]

One end of the HEI pickup coil is effectively
grounded.  On the other lead you will see an
Oscope waveform like this one I took.  If you
were to turn the shaft the other way, the waveform
will be the same. 

The module will trigger the ign on that sharp
negative going edge, which pretty accurately
comes as the pole pieces stop building a stronger
magnetic field and start moving past each other. 
If you reversed the coil wires the waveform would
be upside down, and the module would try to
trigger on that drawn out other transition.  This
would not be at all accurate, besides being half
a cylinder time wise away from the design.  Even
with the HEI turned turned to compensate, the rotor
tip will not be properly aligned with a plug wire
stud, hard to say what will happen then.  Bruce Roe

[TJ Hopland]

I think you pretty much said the same thing I did, makes the timing dynamic mush.   You can get an engine to run but it sure don't like it and you can't change the speed or put a load on it. A real head scratcher if you have never seen anything like it before because it seems like everything is working.     

[Cadman-iac]

  You guys have confused me here. Wouldn't swapping the terminal connections on the pickup coil effectively be the same as reverse winding it, or am I not seeing what you mean?

By the way, on another distributor related topic, did you know that the distributor shaft from a Cadillac is identical to a Chevrolet shaft?
I took the 78 Cadillac distributor apart and noticed that the shaft was worn, and being the curious sort, I took a Chevrolet one and held them side by side, measured the length, checked the position of the hole for the gear retainer pin, all exactly the same.
And, the gears are the same as well, same number of teeth, same angle, same length, everything.
So if you are in need of a new HEI distributor shaft, you can use one from a Chevrolet.
I don't have any Oldsmobile, Buick or Pontiac distributors, but knowing how GM likes to share parts across car lines, I'd be willing to bet that those are the same too.

Rick

[TJ Hopland]

I think some of the 'hot rod' Cad dizzys were chevs that they machined the stop collar off of and replaced it with a clamp on collar. 

I'm not sure what there would be to gain by winding the coil a different direction it would be less work just to flip the wires where they connected to the module.  Its not like one side of the coil itself is grounded. 

Other than needing the correct number of poles and spacing I'm not sure what could be different.  I don't ever recall hearing that there was an issue with high R's so there wasn't a need for a special high speed version.

[Cadman-iac]

 I think I just figured it out. Reverse winding would be that the ground side would be on the outside of the coil, the larger diameter portion, and the positive side would be to the inside, or the smaller diameter part of the coil, or vise versa, I don't know which is correct normally.
 When I was thinking about reverse winding it before I was just thinking of one layer of windings, but instead of starting at the bottom, you would start at the top. It didn't dawn on me that there's a ton of layers of windings, and the field would collapse I believe to the inside, or smaller end.
 I'd have to look that up. But I think that's what you were referring to Bruce.

 Rick

[Dave CLC#16900]

That's very interesting Dave. I would think it would have to be a 5 pin module, as the normal 4 pin has no method of retarding the timing.
How did you work that, tie the 5th wire to a ground circuit on the ignition switch?
And what did you have to do to get the wire through the housing, cut an extra slot for it?
 And where did you find those?

Rick

Hi Rick, Dave Brode wrote about these some years ago on another forum and I bought a couple off of Ebay.  I drove the car yesterday, let me shoot some pictures tomorrow and post them.  I used a relay tied to the starter to retard during crank, don't remember for sure, but think it was to ground the 5th pin.  Stay tuned...