GM HEI Module - odds and ends

[Zed Head]

Realized that we were about to put a serious hijacking on to Eurodat's thread here -

http://www.classiczcars.com/forums/electrical-s30/52621-fitting-hei-module-transistor-ignition-unit-1977-280z.html#post459983

Started this new one.

Here's a link to a post showing the reluctor output from an 85 and an 88 Jaguar, which apparently used the GM HEI module in their ignition system. Looks similar to CO's Post #15 (to my eyes) in Eurodat's thread.

Sean's Jaguar Tech Pages - Lucas Digital P (HEI-based) Ignition Diagnosis

[Zed Head]

Funny, but the GM people call the reluctor, the metal piece with six outward pointing projections, a "timer core". And the stator (the ring in the ZX distributor with the inward pointing teeth, a "pole piece". And I thought the weird simple names in the Nissan manuals were from translation issues.

Here's a picture of the Z and ZX reluctors showing the different shape of the ZX's. The GM timer cores seem to look like Z parts, with no fancy shaping. The ZX part has a ramp up to the trigger point, CCW, top-view.

Here are some links to other reluctor images, various manufactures. Odd that the ZX is different. Geek stuff.

http://www.junkyardgenius.com/ignition/chevy/magcon01.html

http://myplace.frontier.com/~wgmumaw/Distributor%20Conversion/DistributorConversionBills.htm

http://www.lindertech.com/bhrs/chev_8_dist_elec_conv.htm

http://www.msdignition.com/Products/Distributors/Acc_/8415_-_Reluctor,_Dist,_CNC-Machined_Billet_Steel.aspx

Edited July 11, 2014 by Zed Head

[EuroDat]

I think the waves I posted came from Bubba's Hot Rod shop, but I cant find the thread anymore.

http://www.lindertech.com/bhrs/chev_..._elec_conv.htm

I think it was in a mopar forum somewhere. He was one of the threw that made sense in that thread.

Interesting that the Z reluctor looks similar to the original GM units.

[Zed Head]

Here is a 1985 Toyota reluctor. It looks like Toyota also had a module that controlled dwell, before they went to ECU timing control. I haven't figured out which year does what. But the reluctor shape is like the ZX's.

If the right person had posted a Toyota module conversion this whole discussion could be about Toyota modules. They're going for about $42 though, so a few dollars have been saved.

Added a module picture. Too bulky!

Edited July 11, 2014 by Zed Head

[Zed Head]

I think the waves I posted came from Bubba's Hot Rod shop, but I cant find the thread anymore.

http://www.lindertech.com/bhrs/chev_..._elec_conv.htm

One of the links I posted above was from Bubba. About a GM points conversion using Mopar parts. The wrongness...

Pretty interesting actually, maybe the 240Z guys could use it.

[Captain Obvious]

OK, so reluctors and stuff. Here's the pic that started the conversation:

And I did check to see if I have a ZX dizzy, and I do. I hooked it up to the scope and the pickup works, but I didn't get to taking pics yet.

But in the meantime, I had my own "Doh!" moment... You know all that stuff about rotational direction? It's BS. With the Z distributor, the waveforms look the same regardless of which direction you spin the shaft, and here's the reason:

The voltage changes you see on the scope are caused by the changing magnetic field through the wires wound inside the pickup.

You approach the pickup point and the magnetic field increases - Current is induced in one direction.

You reach the pickup point and the field stops increasing - Current stops.

You move away from the pickup point and the magnetic field decreases - Current is induced again, but in the other direction.

But here's the thing... It doesn't matter which way you approach the pickup point from, since the pole of the magnet isn't changing, the current will always be induced in the same direction regardless of what direction you approach from. The steep zero crossing will always be in the same direction regardless of the rotational direction.

The only way to change the waveform polarity would be to use the other magnet pole (which you can't do) or to switch the wires to the scope. In reality, the only way to change the direction of the steep zero crossing is to swap the wires.

Doh! I should have known that... :stupid:

The ZX dizzy changes the waveform a little because of the assymetric shape of the reluctor, but the Z would be the same in either direction. Only way to change the polarity is to swap the wires.

[Zed Head]

Oops. Makes sense, of course. I've even played out in thought the tooth passing the pickup point. Missed that.

So the extra metal in front of the tooth on the ZX reluctor. That might get the voltage back above zero sooner maybe? You have your Z trace centered peak to peak and the trace between the peaks looks even top to bottom and side to side. If so, I'd guess the ZX trace might be a little asymmetric. Don't know.

You're not going to hook up a coil and measure dwell times and output are you?

I'm going to see if I can find out more about the Toyota module. I'm obsessed now.

[Zed Head]

Found a 4 pin Honda module with dwell control - Honda OE# 30120-PA6-921, 30120-PB1-006 Ignition Module

Compare to another with ECU (ECM) control - Honda OE# 06302-PT2-000, 06302-PT2-A00 Ignition Module

One could spend a lot of time exploring 1980's ignition systems. Lot of odd stuff out there.

[Captain Obvious]

Yeah, it makes perfect sense to me too now, but it would have been better for my self image if I had figured that out before I saw traces on the scope that made me go "huh?" You're not spinning a bipolar magnet past the pickup alternating poles like a generator. You're just moving one of a number of the same polarity pole towards the pickup from one side or the other. I don't know if they are all N or all S (and it doesn't even matter), but all the poles are the same.

No, I'm not going to measure dwell as that is more a function of the electronics in the module, not the reluctor design. Also, I don't have a ZX ignition module as it's already been harvested off the ZX dizzy that I have. All I've got is red and green pickup wires sticking out the side of the module.

I'm obsessed now.

Yes. Yes, you are.

[Zed Head]

Found an alternative to Pertronix for the points guys - Electronic Ignition Module Kit K2543

[Captain Obvious]

I got some new pics.

Here's the ZX distributor spinning the correct (as used) direction:

And here's the ZX distributor spinning backwards(as used). You can clearly see the asymmetry caused by the shape of the reluctor. Someone way smarter than me would be able to explain why that difference is so much more pronounced in one direction that the other. Probably has to do with all that black magic like flux density and the hysteresis of the B-H curve.

However, since it's spinning the wrong direction, it's purely academic. Here's the pic:

Here's the wire polarity I used for the ZX dizzy. I didn't research how it's really used in the ignition system, but for these pics I used red a positive and green as negative:

And I dug back through my pics and found this pic of when I did the Z distributor. For those pics I just arbitrarily connected wires and at that time I used green for positive and red for negative. That's why the polarities are different between my Z and ZX pics.

[SteveJ]

Interesting concept.