Electronic Distributors From Rick Ehrenberg

if the car is manual this may be useful if its not i'll agree something else is wrong on the electrical side of things ....

Your alternator can, at the point of an unexpected switch off, produce a spike in the electrical system.
when running, the armature in the middle, has a current flowing which converts it into a big spinning multi pole magnet, like the one in a dynamo.
that field is dragged at high speed past the main windings in the case, driving a current in them.
this is in most cases an AC 3 phase set up.
Those 3 AC currents at a voltage higher than 14V are rectified into a 12--14.5 volt DC current to charge the battery and run the car.

If your battery is flat-ish and the alternator is doing its best to sink 20+ amps into it
i.e you are revving the engine on a manual car, to pull away after a cold start and the alternator is working hard.

a stall at this point can cause a spike in the electrical system.
everything is still switched on at this point, just the engine stopped abruptly.

the alternator is limited in its output:-
1) By the winding configuration 36 amp alternator makes nominally 36 amps
2) By the back EMF created by the processes that creates the DC output in the first place. You get to a point where no matter how fast the thing spins its never going to make more than 30 amps or so i.e the current in the armature makes it a magnet with a magnetic field that is spinning fast, which is creating a current in the coils around the case. the current in the coils around the alternator case creates a magnetic field, because of course, that current is also flowing, and a flowing current makes a magnetic field that resists the impact of the magnetic field created by the armature.

the alternator has a built in self limiting design.
but both parts have a field around them when its working, and that filed will collapse when it stops abruptly

if the motor stalls at a point when the alternator is FULL ON the spinning armature stops and the magnetic field it creates stays in place but stops moving abruptly. But the field around the coils in the case collapses.

this can produce a spike on both the field terminal and the main battery + terminal that is going the other way from normal.

no real impact on a mechanical regulator or a set of points

But potentially some impact on an ECU.
the higher the rating of the alternator the larger this spike can be

An electronic regulator is better at isolating any spike back on the field wire to just its own circuit, so its unlikely to get back to the fuse box/ main splice and hence to the ECU or coil

the spike on the B+ wire will be dependent on where the alternator stopped where the poles of the armature are in relation to the 3-phase coils in the case. the voltages in these coils when operating are greater than the DC output voltage of the alternator because the peaks and troughs of the 3 waves of AC need to be combined and hammered flat by the diode based rectifier into a DC output between 14.3 and 14.7 volts

as such in theory you could get something negative at the b+ terminal and depending on how abruptly the alternator stopped, the crash of the field around these coils could be rapid and make a noticable spike of 10s to 100s of volts for a very short, as in milliseconds, period of time.

the condenser in the distributor can help combat this issue
a diode connected to coil negative can help combat this issue (do a search for dave999 zener diode and you will see what i did)

I have broken 5 or 6 ignition modules over 20+ years, they have tended to die when i have been at the track. i drive no faster on the track than i can achieve illegally on the road just on the road i do it for way longer and when stuck in traffic way hotter.

what is common amongst failures
1) At the track the car battery is used a lot for starting the car and charging things, so its not exactly fully charged by the second or 3 day of racing, beering, and talking BS. I'm not in the pits and i don't own a generator.
2) We tend to be camped on uneven ground in deep grass, and as this was a WWII airfield before it became a track, ruts, holes and unseen depressions, one presumes some bombs landed and some planes missed the runway....
3) The car is often very cold and damp when first started
4) I have less than useful reverse ratio in my manual box
5) On the occasions where i have tried to reverse out of the site where we are camped and have stalled it at reasonable RPM, ammeter pegged right, Instantly or within hours i have a failed ignition module.

My experience doesn't make it so, doesn't make it a thing... i could be wrong, However its the only explanation i can come up with.
My alternator is good decent DC output no failed diodes

I have learned a lesson and i no longer have failed ignition modules not for a very long time.
careful use when cold and stuck in the field
a nice zener diode

what can cause an alternator to switch off abruptly?
1) stall the car
2) loose field wire
3) worn out or sticking carbon brushes

i think it would be mighty bad luck to experience this in an auto trans car
i think it would be unlikely you would come to my conclusion with an auto trans car

but i think it is well known that unexpected spikes on the electrical system can kill an ECU

if nothing else fits try a diode like i did

VS-40HFR40 Diode Stud mount

screw it into a grounded bracket or the body, i just used a tab on my coil mount.
run a wire from the exposed end to the coil negative, see if your ECUs last longer

switching the ignition off with the key/switch doesn't cause a problem because at that point you disconnect Ignition from the electrical system.....


Dave