GM HEI on a '78 280z and no start

[Usain_Boat]

Hey all, I did the transistor ignition unit upgrade as described here: 

Given this though, I have had some problems after doing it.

Given that I have a '78 I don't seem to have a resistor below the ignition coil but I think I wired the HEI module in correctly. I think it is correct since it ran for over 6 months, and the last 7 weeks of that was the car being driven daily.

On the 7th week though, problems began. The car became slowly harder to start taking longer and longer to crank until it eventually stopped firing all together. 

I have checked and the car has fuel and air, just no spark. Seeing this, I replaced the HEI. After replacing the HEI the car stumbled as if it would fire and then resumed cranking with no spark.

So, have I installed the HEI correctly for a '78 280z? If so, what else could be killing HEI modules when I replace them?

 

I have attached pictures of my module installed: 

 

[Racer X]

13 minutes ago, Usain_Boat said:

Hey all, I did the transistor ignition unit upgrade as described here: 

Given this though, I have had some problems after doing it.

Given that I have a '78 I don't seem to have a resistor below the ignition coil but I think I wired the HEI module in correctly. I think it is correct since it ran for over 6 months, and the last 7 weeks of that was the car being driven daily.

On the 7th week though, problems began. The car became slowly harder to start taking longer and longer to crank until it eventually stopped firing all together. 

I have checked and the car has fuel and air, just no spark. Seeing this, I replaced the HEI. After replacing the HEI the car stumbled as if it would fire and then resumed cranking with no spark.

So, have I installed the HEI correctly for a '78 280z? If so, what else could be killing HEI modules when I replace them?

 

I have attached pictures of my module installed: 

 

Have you tried replacing the GM ignition module? They do die periodically, and you mention that the car ran fine for 6 months, so get one and swap it out. I have owned several GM vehicles with that ignition module, and learned early on to keep one in the glove box, along with a screwdriver for changing it out. Saved me on more than one occasion. I also worked as a mechanic for 30 years at a local electric utility, and the fleet was mostly GM. I lost count of how many of those modules I changed out over the years.

[Usain_Boat]

I have changed it, but it appeared to die immediately. 

Should I get another to try again?

[Zed Head]

Check the inside of the distributor.  The triggering mechanism can wear, there's an air gap to set.  The magnetic pickup coils go bad also, there's a resistance measurement to take.

[Racer X]

13 minutes ago, Usain_Boat said:

I have changed it, but it appeared to die immediately. 

Should I get another to try again?

No, not yet. There are other things to look at.

Like:

6 minutes ago, Zed Head said:

Check the inside of the distributor.  The triggering mechanism can wear, there's an air gap to set.  The magnetic pickup coils go bad also, there's a resistance measurement to take.

 

^^^^ What he said. ^^^^

Edited November 27, 2020 by Racer X

[Usain_Boat]

It was the pickup coil too far out.

Is there a torque spec for those screw, or are they just a thing to check occasionally? I remember gapping this not too long ago.

Just for my piece of mind, the HEI is installed correctly for being a '78?

[EuroDat]

That is a nifty 👍heat sink you fitted to the HEI module. One thing that can destroy a Hei module is poor grounding. It grounds through one of the mounting screws. Do you have good contact to the car body under the heat sink?

When I started playing with this idea, I used an el cheapo test unit. I ordered two and they both lasted about a week each. The Pertronix HEI module has been in there since without any issues.

 

[EuroDat]

10 minutes ago, Usain_Boat said:

It was the pickup coil too far out.

Is there a torque spec for those screw, or are they just a thing to check occasionally? I remember gapping this not too long ago.

Just for my piece of mind, the HEI is installed correctly for being a '78?

I can't follow the wiring in the photo, just going by the colours. Coil negative goes the HEI module terminal C and 12v goes to HEI terminal B.

The green and red are correct.

PS: Good to hear you found the problem.

[Usain_Boat]

The coil negative is the blue wire that goes to terminal C and positive is the black that goes to the B terminal. The screw that is on the grounding lug shows 0 Ohms to ground, so I believe it is properly grounded.

The heatsink is mounted where the old junction from the pickup coil was, as the transistor ignition unit it led to is no longer in the car.

 

[Zed Head]

1 hour ago, Usain_Boat said:

Given that I have a '78 I don't seem to have a resistor below the ignition coil but I think I wired the HEI module in correctly.

So, have I installed the HEI correctly for a '78 280z? If so, what else could be killing HEI modules when I replace them?

The wiring is the same without the ballast resistor.  If it ran for 6 months it was probably right.

Check the play on the distributor shaft.  That will affect the air gap.  The screw is just as tight as you can get it with a hand screw driver.  Sounds like yours just came loose. 

You're saying that you reset the gap and it runs now right?  You're probably good to go.

[Usain_Boat]

4 minutes ago, Zed Head said:

The wiring is the same without the ballast resistor.  If it ran for 6 months it was probably right.

Check the play on the distributor shaft.  That will affect the air gap.  The screw is just as tight as you can get it with a hand screw driver.  Sounds like yours just came loose. 

You're saying that you reset the gap and it runs now right?  You're probably good to go.

Yes, after resetting the air gap on the pickup coil, it runs again. I plan to test the old HEI as I assume it is still good.

[EuroDat]

15 minutes ago, Zed Head said:

The wiring is the same without the ballast resistor.  If it ran for 6 months it was probably right.

Check the play on the distributor shaft.  That will affect the air gap.  The screw is just as tight as you can get it with a hand screw driver.  Sounds like yours just came loose. 

You're saying that you reset the gap and it runs now right?  You're probably good to go.

The air gap is important on the 280Z pickup. If the voltage generated by the pickup can not reach 0.3volts the HEI module will not activate. A wider air gap will reduce voltage.

These pickups at best will generate 0.5 to 0.8volts at cranking speed. The later 280ZX distributors have a better designed pickup which will produce much more voltage at cranking speed.

Edited November 27, 2020 by EuroDat
Voltage