Fitting a HEI Module in Transistor Ignition Unit 1977 280Z

[HusseinHolland]

Put the new GM HEI module on a heatsink with heat sink compound, and made a strip to bypass the ballast coil. I'll test it out soon. Trying to get the interior back together at the moment

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[HusseinHolland]

Reinstalled the 12 volt Volvo coil, and the bypass for the ballast resistor. Plugged in the original HEI module I had installed, and the car started right up. The problem all along to low cranking speed with somehow impacting the spark? Not sure but now it works. Problem is the tach no longer works. Before digging through the whole thread, does anyone know if I have to replace the resistor for a different value or remove it?

[Zed Head]

I had a similar problem and found that installing a condenser/capacitor on the negative post of the coil made the tach work.  I don't have the knowledge to put any math on it but my theory at the time was that the HEI module created more electrical noise, that affected the tachometer.  But over the years I've found more about "kickback" or "flyback" from the coil field collapsing causing electronics problems.  So maybe that's part of it.  Whatever it is, the capacitor worked.  It was just a common alternator radio noise suppression unit. 

Here's something from a Ford manual describing the kickback.  Also an image of their "ignition transformer capacitor".  It's one of those odd things that is there in print but very little words are used to describe how it actually functions.  This system is controlled by the PCM, not an external module.

Short story - a capacitor on the negative post might fix it.

[HusseinHolland]

2 hours ago, Zed Head said:

I had a similar problem and found that installing a condenser/capacitor on the negative post of the coil made the tach work.  I don't have the knowledge to put any math on it but my theory at the time was that the HEI module created more electrical noise, that affected the tachometer.  But over the years I've found more about "kickback" or "flyback" from the coil field collapsing causing electronics problems.  So maybe that's part of it.  Whatever it is, the capacitor worked.  It was just a common alternator radio noise suppression unit. 

Here's something from a Ford manual describing the kickback.  Also an image of their "ignition transformer capacitor".  It's one of those odd things that is there in print but very little words are used to describe how it actually functions.  This system is controlled by the PCM, not an external module.

Short story - a capacitor on the negative post might fix it.

Many thanks - I'll try adding a condenser - I have a spare from a Volvo - there is one already on the positive side, but I'll leave that one alone.

 

[HusseinHolland]

6 hours ago, Zed Head said:

I had

 

Duplicate

Edited October 28, 2023 by HusseinHolland

[HusseinHolland]

So that didn't work out. Adding the condenser, the engine would not start at all. . It shorts out the coil pulse. Checking ignition pulse with the test light the way I would with most systems doesn't work- it actually feels like it's killing the ignition. I'll have to try it again with the regular coil and module and see if it pulses normally.

Edited October 29, 2023 by HusseinHolland
edit voice to text errors

[Zed Head]

21 minutes ago, HusseinHolland said:

Adding the condenser, ... It shorts out the coil.

Not sure what went wrong for you but "shorting out the coil" is not possible if the capacitor is intact.  Capacitors don't pass current.

Any chance you connected it backward and blew it up?  Center lead to coil post, body to ground.

[HusseinHolland]

25 minutes ago, Zed Head said:

Not sure what went wrong for you but "shorting out the coil" is not possible if the capacitor is intact.  Capacitors don't pass current.

Any chance you connected it backward and blew it up?  Center lead to coil post, body to ground.

I used an ignition coil suppressor, not really any way to mis-connect it, as you said, lead goes to coil, tab on housing is ground.

For whatever reason, hooking up a test light to the coil or to the tach feed in the cabin results in a noticable miss in the ignition. Adding the suppressor to the (-) coil terminal prevented it starting, period.

What type of capacitor did you use?

For the time being I put the stock system back in place.

Edited October 28, 2023 by HusseinHolland

[Zed Head]

I think that I used one of the typical Nissan postive side capacitors then switched to a typical alternator capacitor when the wire broke on the first one.  I just mounted it on the main ground point on the intake manifold.  In my case the tach needle would quiver but not move without the cap.  That's how I found that the first was broken, when the tach stopped working again.  So, two different caps, both solved the problem.

Did you check continuity through your Volvo ignition suppression cap?  Should be none, of course.  Maybe a quick beep as it loads up.  Maybe the Volvo unit sucks up too much current and screws up the charge cycle.

Could be that the system is finely balanced and I just got lucky.

[HusseinHolland]

On 9/1/2019 at 6:26 PM, kyle146 said:

Ok so update time! Been driving the car all week with the wires reversed and ballast resistor still active. Today was the day I wanted to bridge the ballast resistor. After I bridged it, it started up just as normal and ran fine. Only little issue was the Tach was freaking out. It was stuttering and all over the place. To rectify the issue I turned off the car, Reattached the resistor terminals to the resisted side and started it again. Tach functioned like normal. I had then Isolated it down to either the grounding was bad or the Blue in line resistor underneath the glove box area was not enough. So I cleaned grounds and bridged the resistor to 12 volts again... same thing, tach all over the place. I then grabbed a 5k Potentiometer I had made with bullet connectors and put it in line with the resistor. Tach functioned fine until I revved and then acted slightly erratic again but not too much. Which told me that I needed a higher resistor. Pulled out a 10k Potentiometer with bullet connectors and connected it just by itself and adjusted the knob to about halfway and started the car. Tach worked perfectly and if it was a little slow I would just turn down the knob a little. Ill be driving all this week with it on 12 volts. I even cleaned and gapped the spark plugs for the new spark it will be receiving.  

This was the post I was recalling - he had a similar issue. Before I switched back to the stock coil & module, I had measured the stock resistor - 2.23K ohms. I added a 2.2K pot in place of it, and tried  lowering the resistance - needless to say the tach didn't work. I'll try again with a 5 - 5.5K ohm resistor 

 

 

[HusseinHolland]

47 minutes ago, Zed Head said:

I think that I used one of the typical Nissan postive side capacitors then switched to a typical alternator capacitor when the wire broke on the first one.  I just mounted it on the main ground point on the intake manifold.  In my case the tach needle would quiver but not move without the cap.  That's how I found that the first was broken, when the tach stopped working again.  So, two different caps, both solved the problem.

Did you check continuity through your Volvo ignition suppression cap?  Should be none, of course.  Maybe a quick beep as it loads up.  Maybe the Volvo unit sucks up too much current and screws up the charge cycle.

Could be that the system is finely balanced and I just got lucky.

There must be more going on with mine. The fact that adding a test light to the (-) coil terminal disrupts the system seems like a problem to me.

I didn't check the suppressor. Volvo used Made In Japan suppressors ((+) side of coil connection), so it should be happy on the car 🤪

Edited October 29, 2023 by HusseinHolland

[Zed Head]

I completely overlooked what you were saying about the test light on the coil while the engine is running.  The test light passes current so would not give a clean "break" of the coil primary circuit.  The magnetic field collapse would be messed up.  Not sure exactly how.  Surprised the engine didn't just stop sparking, actually.  Make and break is the key to create spark.

p.s. if your Volvo capacitor is passing current it would have a similar effect.

Edited October 29, 2023 by Zed Head