1978 2f + Stock Distributor + HEI ignition module

[Freeborn]

Has anybody run this combo successfully?

Story:
I have a freshly rebuilt 2f with Sniper for fuel delivery. I was running a DUI HEI for spark for a while after the ignitor that came with the truck died. This week I thought it might be cool to see if I could get things to work with the stock distributor. I finally got the proof of concept wired up this afternoon and got it to start and set idle timing. The thing I'm running into is that the minute I step on the gas (not in gear, just in the garage) it dies immediately. I'm curious to see if there's something I'm missing like a mismatch in the strength of the pickup coil output. More generally I'm interested in hearing others' experience in similar situations.

 

[65swb45]

I remember an FAQ from @Poser about this exact mod…over 20 years ago.

Did you try the FAQ?

 

[nabbasi]

I could not get it working with a few of the aftermarket igniters mentioned here over the years. I ended up going with a non-USA distributor and a relay to get full power to a Pertronix coil.

 

[numby]

Just guessing here but since the HEI module determines the dwell maybe there's a conflict somehow with what the signal generator is telling it? A classic symptom of frozen points in a traditional distributor is a good idle but dying when trying raise rpms or accelerate.

 

[Freeborn]

I figured it out. Actually, I’m a little bit ashamed and surprised that Chatty-G provided some good direction. When I took the ballast resistor out of the equation as a diagnostic step it ran amazingly. Since the stock coil isn’t made for a constant 12v I grabbed a MSD coil and simplified my wiring. The thing runs awesome. Here’s what it looks like (for now).

 

[65swb45]

I figured it out. Actually, I’m a little bit ashamed and surprised that Chatty-G provided some good direction. When I took the ballast resistor out of the equation as a diagnostic step it ran amazingly. Since the stock coil isn’t made for a constant 12v I grabbed a MSD coil and simplified my wiring. The thing runs awesome. Here’s what it looks like (for now). View attachment 4166759

If you could sketch a quick diagram of where the four wires go AS PICTURED IN THIS POST, and tag the post with HEI module, the community will benefit for decades to come.

 

[arlenroy]

If you could sketch a quick diagram of where the four wires go AS PICTURED IN THIS POST, and tag the post with HEI module, the community will benefit for decades to come.

Yes, please. That's my next upgrade, it would greatly appreciated and you'd save a lot of us time. Thank you!

 

[Freeborn]

Here you go...
I wired mine up with a relay. I don't think it's necessary as I'm pretty sure the original wiring was directly to the black/yellow wire indicated in the diagram. If you're into anti-theft wiring, the relay can be handy.

As mentioned above: ONLY USE A COIL THAT CAN TAKE A CONSTANT 12V LIKE THE ONE PICTURED. From what I understand (and I'm no expert) the stock coil will melt if wired without the ballast resistor. I grabbed this MSD coil at Advance Auto Parts for about $60 and they had it in stock.

 

[Freeborn]

One final pic. I added a heat sink I found on Amazon (that’s supposedly for these ignition modules but required a bit of modification).

Why?
Because heat kills these modules. When they get too hot for too long they die without warning. Ask me how I know.

Tips:
1. As mentioned above, use a thin coating of thermal paste between the module and the heat sink. This is distinctly different from electrolytic grease that they try to give you at the parts store. The stuff you want is the same stuff that they use between CPUs and heat sinks. Electrolytic grease will not work. Ask me how I know.
2. Keep a spare ignition module (or two) in the truck. It’s cheap insurance. When, not if, the module dies, you can be back on your way in minutes.

 

[rlong]

That’s all good advice! It’s always heat with components like that.

 

[numby]

Two points here...

1. Make sure you're using the old school 4 pin modules that first came out in 75 or so. There are ways of adapting the later 3/5/7 pin versions but why torture yourself. Supposedly you can even trigger them with points but I've no clue how.

2. On 78 models the pink Yazaki(?) resistor wire in the BY wire from the ignition switch should provide enough resistance for standard coil use. About two years ago I went through a heavy miss above 2K rpm when my old no-name HEI bought the farm and I went back to an OEM points dizzy. When I pulled the ballast resistor out of the system the miss went away. To be fair I only ran points to 500 miles of so before I switched to a Pertronix set-up but there was no evidence of pitting or a hot coil. That's been in for roughly 2500 mi. so not a real long time. The coil is just a basic Standard Motor Products item. I mention all this because you might not really need to run a relay depending on other components in you setup.