So I stumbled on an interesting HEI phenomenon

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Voeltagear

Voeltagear

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Has anyone had this happen? My alternator gave up the ghost on the way to work yesterday and something strange happened. Every time I would turn the blinker on the ignition would cut out. ON, OFF, ON, OFF, ON, OFF... very strange. Seems the low end of the HEI module operating voltage is around 11.8 volts? Battery held in for 8 miles or so then I couldn't even accelerate from a stop without stumbling and then stalling eventually. Weird thing is the battery still cranked it up no problem. Lights were bright. Would idle fine. Battery turned out to be way down on cranking amps but still enough to turn a mini starter. Changed the Alt and battery so now its fine. Just was seeing if anyone had any experience like this with the HEI mod. Very easy Driveability Diag though- turn the lights off, problem goes away. Must be electrical! LOL
 
Is your feed wire still going through the ballast resistor? I would make sure you have battery voltage to the coil and module.
 
No Ballast resistor on this one (or any of mine anymore), HEI mod done. Problem was the "battery voltage" was too low due to alt not charging. Interesting how it presented itself. I tried hooking up the old battery without the alt connected and it did the same thing again after charging it. With the new battery and no alt it runs just fine. Soo battery is bad and The old alternator didn't put out any amperage.
 
One question I'd have is where were you measuring the voltage? And do you know what the drop is actually right at the HEI?

On the other end, "all this stuff" seems to have a low limit.

One of my big bitches was back when I used to be more active in amateur radio. I believe the worst as I recall was my Yaesu FT- 890. Dam thing did NOT like low batt. voltage---exactly what you might "have" if you were in some emergency situation, or even just "operating portable"

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i changed from points to hei on a 70 firebird years ago and used the wire to the positive coil to the hei battery feed it would idle fire right up but stumble and have no power.the hei module has to have 12 volts minimum to work right ....
 
There are likely dips in voltage with a weak battery, that go well below what is measured with voltmeter. A scope shows the real picture. Automotive electronic designs often incorporate a cutout for low voltage. While in your case, the engine misses, there can be more severe problems without the cut out, including damaged electronics. The gate drive for power semiconductors need to operate at specific levels, too low and the driver partially activates and may destroy the junction.

I design with logic level drivers, so my EMC unit will work down to 7 volts. The circuit runs on 5V but the regulator needs 2V of head room.
 
The voltage that counts is from the HEI "power input pin" to its case. You could have 2 V drop thru the mounting screw if relying on that for a ground (and were already marginal). It could also be a transient drop, so would have to view the dV on an O-scope to know for sure, as Kit says.
 
Well I'm not looking to play around with it too much. I'm afraid I'd end up buying another ignition module if I run it too much more. I have a scope for the modis at the shop. The Battery I was using was an Interstate Optima red top from 2000! I talked to the Interstate rep today when he came to exchange cores and batteries and He said the Spiral cell Batt from that time period were very good and lasted around the same number of years as mine. I have a feeling even though the battery was reading 12.5 volts there just wasn't enough current being generated by the "plates" and electrolyte. Or is the word I should be using watts since it also seemed to be a function of how long the draw was applied to the battery? It tested to about 255 cca of 800 but that is the Interstate ED18 tester and it only pulls current for a short time. Thats why I could start it after a few minutes and it would drive another few blocks before shutting down. The Battery also caused the charging system, after I replaced the alternator, to run above 15.1V. (tried 2 different regulators) The new battery runs 14.4-14.5V.
 
While working at a Ford dealership, customers would come in with same problem, "starts and drives but runs like crap". To tell them they needed only a new battery would often lead to argument, especially when they heard what the battery costs there.
Starters, lights, etc.. will operate on 11 volts. The difference in how they are operating, starter turning slightly slower, lights not quite as bright, is difficult to recognize. The electronics are very sensitive to low voltage.
I'm glad it was the service advisors job to try explaining these things to customers.
By the way.. I've seen batteries that were so bad, put a meter on it and see 12.2, open the door and the dome light alone would drop the meter reading to 2.9 in a heartbeat.
 
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