77 280z Restoration

[Zed Head]

The question I raised is whether the timing is retarded or not, meaning that the timing would change when you switched modules.  Since you would normally set the timing for just one module after installing it you wouldn't know if the retarding mechanism was in play or not. 

It's not about how it works but how the two different modules compare.  Even the base setting, of either, might have a delay based on the internal circuitry.

A timing measurement will tell.

[Av8ferg]

Okay, I get what you’re saying and yes it appears the timing has changed with the HEI on.   Warmed it up and put my timing light on and it was off about 3-4 degrees (retarded) at 800 rpm.   I reset it to 10 deg and she’s now even running smoother,   I took it out for a 30 miles drive and had no issues.  Well, I thought I had one but I’m coming to believe my temp guage or sender  it’s very accurate.  I bought a radiator cap with a thermometer in it as a back up and it was showing much cooler than the temp guage.   Took my son through a drive through  for lunch and them temp gauge really creeped past mid range.  I pulled over and the cap on the radiator was reading about 180 ish.  So I’m missing the lower half of a fan shroud and don’t currently have the lower skid plate installed, not sure if that’s a factor.   I’ve kept it off until I take the car to a shop to make sure the alignment is good.   I did it the good of’ boy method.  Eye ball it while drinking a beer, but she tracking  perfectly.  Maybe I should drink beer more when working on the car.  It got even higher than this pic my son took. 

[dutchzcarguy]

14 hours ago, Av8ferg said:

but she tracking  perfectly.

 

14 hours ago, Av8ferg said:

Maybe I should drink beer more when working on the car.

Yes,  ...... and less when writing on this site!  (when i look at your sentence structure!  😉 )

[Dave WM]

just curious is then temp sending unit the one piece type or the two piece? I recently installed the 1 piece and it seems to indicate higher than the actual water temp using a thermometer.

[Av8ferg]

Well when typing in a small phone with big fingers and “auto correct”  turned on mistakes are made.  I🤓

[Av8ferg]

Dave the sending unit is a single female type bullet connector.  Is this the one you’re talking about? 

[Captain Obvious]

21 hours ago, Zed Head said:

Since you would normally set the timing for just one module after installing it you wouldn't know if the retarding mechanism was in play or not. 

It's not about how it works but how the two different modules compare.  Even the base setting, of either, might have a delay based on the internal circuitry.

That's a really good point there. You set the base timing using one of those two modules, but there's really no guarantee that the output timing from the other one will be the same. Could simply be that the propagation delay through the modules are different, or it could be something way more significant than that.

I know that GM put a "cranking mode" base timing setting into a lot of their later modules used as a bootstrap mode to fire the ignition before the computer was able to take over. Now that's for the later modules that used an ECM to control the timing after the engine was running, but they may have put something like that in the earlier simpler non-ECM controlled units too. And if they did, the question is... How does that relate to the rotational position of the VR pickup titts?

And now that I'm thinking about it, I thought of something else... I know the earlier modules (up to 78) fire directly when they receive a pulse from the VR pickup, and they fire on the rising side of the VR signal. Many (most?) of the rest of the later modules fire on the falling edge? I don't remember what GM did, but I will look into it. I should have thought of that before. Arrgh.

Bottom line is put a timing light on it and see if you're OK. You might have to pick one style as primary and the other as 'backup only".

[Zed Head]

The fact that the engineers must have designed algorithms that converted degrees to time (very small intervals of time) in to the ignition system has been in the back of my brain since I started learning about them.  I wonder how accurate it could actually be.  And it must be more accurate at low RPM.  I wonder if weird stuff happens if you use the retard setting at high RPM.  It would be interesting to compare high PRM timing between the two modules.  

I've always read that the GM HEI module used a positive crossing trigger.  The rising edge.  But, another thing that's been in the back of my mind is that silicon transistors switch at 0.7 volts, apparently (not a semiconductor expert).  People use the GM HEI module in place if the "ignitor" on the 280ZX Turbo ECCS ignition systems.  Which should never go negative, it should just have a zero to 5 volt square wave.  Maybe the HEI module has circuitry that works on a zero transition though.  Not my field.  If it has to cross zero it should not work in the ZX ECCS system.

Anyway, it was fun to learn something new about these two modules.

 

Lots of interesting stuff about the GM HEI modules in the Megasquirt world.

http://www.megamanual.com/ms2/GM_7pinHEI.htm

Edited September 20, 2022 by Zed Head
+ X Turbo

[Captain Obvious]

12 hours ago, Zed Head said:

I've always read that the GM HEI module used a positive crossing trigger.  The rising edge. 

I did the same digging you did and that page turned up on my radar too. On that page they indicated that the simpler 4-pin GM HEI module used a positive transition, but the other later modules used positive to negative. I have not verified this myself, but they say:

"The 4-pin HEI uses a negative-to-positive transition, while the 7/8-pin uses a positive-to-negative transition (though this *might* have changed in some applications). Thus polarity of the reluctor signal is critical to proper function."

I've poked around a bunch with the Datsun modules they put by the passengers feet (up through 78) and those fire on the rising edge of the VR pickup. I've got a couple of the later matchbox ignitors here, but haven't checked them.

Here's a couple pics of ignition module waveforms. This is a 77 module being driven by a ZX distributor (so the shape of the VR is a little different than previous years). This should be about 6000 RPM engine speed. Note that when the output signal goes high, it releases the coil and initiates a spark. You can see that it sparks on the rising transition.

And here's a 78 module om my newer digital scope. Note that I'm not using a real VR input on this one, I'm just using a signal generator to provide a simulated input signal. But the important part is that it also fires on the rising edge. This is 6000 RPM.

I know we are getting off topic here and if anyone wants to get all real geeky with the ignition modules, let me know and I can start a thread with that intention.

 

[Captain Obvious]

I will check a couple of the distributor mounted matchbox modules when I get a chance. I've got a couple tossed in a box that came from who-knows-where. I'm sure some of them work. Probably. Maybe? At least at room temperature.

[SteveJ]

2 minutes ago, Captain Obvious said:

I know we are getting off topic here and if anyone wants to get all real geeky with the ignition modules, let me know and I can start a thread with that intention.

 

Me! Me! Me! I want to get geeky! I even started playing with the inductive pickup I bought for my scope. I really need to re-familiarize myself with working with o-scopes. It was a LONG time since collage.

[Captain Obvious]

4 minutes ago, SteveJ said:

It was a LONG time since collage.

https://en.wikipedia.org/wiki/File:Hamilton-appealing2.jpg

Hahahaha!!!!