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77 280z Restoration


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5 hours ago, Zed Head said:

Apparently the E12-92 retards timing by 8 degrees, but it's not clear exactly when.

The E12-92 will work identically to the E12-80 if you only connect up the "C" and "B" connection on the top of the module. The other connector is what controls the retard, without that connection it functions the same as the E12-80. I've been running a E12-92 for about 20 years now on my 240Z and it runs great.

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That’s exactly what my research led me to believe.   Without other connector attached it operates as an E12-80.   I think Zed Head had a good point and I will still place a timing light on the engine today and see where it’s at.   Before I did all the ignition changes it’s was spot on at 10 deg at 800 rpm and the mechanical and vacuum advance was perfect.  Off the top of my 17 deg of mechanical advance with a total around 35 at 3000 rpm.  Don’t quote that.   I’d like to find an adjustable vacuum advance Part number 22301-7901 and replace mine.  Would be fun to mess around with the advance curve and see how it effects performance.  

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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.

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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. 

31E19D58-BD36-4E2E-B5EB-E8706586F348.jpeg

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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".

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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 by Zed Head
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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.
P1160646.JPG

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.
P1200608.JPG

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.

 

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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.

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I have many questions.  Can't wait.  Maybe some Pertronix or 123 modules can be looked at, to compare.  Or David Vizard's 4500 RPM limit (V8) for the HEI module.  Many unanswered questions floating around out there.

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On 9/18/2022 at 10:34 AM, Av8ferg said:

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

there is a two piece with the sender mounting into a separate screw in brass holder and then there is the one piece where the sender and the screws are all one brass piece. the OE is the two piece with separate screw in / sender bits. I did not know about this, ended up with the one piece which fitment is the same, came with a O ring (not used not sure why its included). It seems the seal is made by the conical shaped end of the sender in both types. 

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Very interesting ignition discussion!  I have some info on fuel injectors that I read many years ago. The injectors in our Z’s need cleaning more often then those a generation late.  The vintage of injectors in our Z’s we’re tested by running a test engine for many hours continuously and there were no issues with gumming up. What they missed was that an engine doesn’t run continuously during its life.  When the inservice engine was shut off a bit of fuel would remain in the injector, evaporator and leave behind varnish. That would make the injector slow to close after the electric signal was cut off and would lead to a fuel mixture that was too rich. Later generations solved this problem though I don’t remember how. 
The most effective way to clean was a cleaning kit that consisted of a pressurized can of concentrate cleaner that could also serve as engine fuel and the associated plumbing to connect this to the fuel rail, control the pressure and a pinch clamp to block off the gasoline return line. (I think you blocked the supply by pulling the fuel pump fuse, but I don’t remember for certain.)

When I owned my 76 (bought it new), I owned one of these kits and it worked very well.  

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Sorry I don’t recall a reference. I read this more than two decades ago when I was trying to figure out if my 95 Ford engine needed the injector cleaning that my Z got.  The 95 went well over a 100,000 miles and never needed the injectors cleaned.  The 76 Z couldn’t pass our Phoenix, AZ area emissions test if the injectors weren’t cleaned more frequently.  It would run too rich. Nothing that was noticeable in performance, just failed emissions on high HC. 

Sometimes as an old guy you wonder why you remember certain things with great clarity and are vague recalling things of far more importance!

 

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