1970s HEI "eating" ignition modules

["Cadillac Kid" Greg Surfas 15364]

Well it seems to be happening to me too. I'm just getting a few thousand miles on ignition modules. Connections are good, coil, cap and rotor are good (DUI), and the ground is a full size battery cable from the negative post of the battery to the front of the block. Anyone have any suggestions THAT CURED THEM OF THE SAME ISSUE?
Greg Surfas

[Dave Shepherd]

I am sure you are coating the mounting  area with the heat sink paste.
Also the coil ground wire circuitry has been confirmed.

["Cadillac Kid" Greg Surfas 15364]

Yes Dave. Both those things are and were ok
Greg Surfas

[TJ Hopland]

Have you checked to see what voltage you are getting at the distributor during various operating conditions?   Easy enough to test just to make sure its not low or high. 

[bcroe]

My exerience with integrated circuits and
electronics failing in cars, is big voltage
spikes can cause them.  Here a circuit failed
a couple times when the car was started, was
working at previous shutdown.  It was found
that the starter could generate spikes of
300V, though extremely short and not a problem
for things like motors and lights.  Now I use
high frequency filters much like the 12V inputs
to radios, maybe a 24V TransZorb added to help. 
There is a 12V cap in the HEI, might check it
is good. 

A generator might also be suspect, all HEIs used
an alternator, probably without an external
mechanical regulator. 

Possibly the ign coil could could be kicking
back excessive voltage, bad or a lot of impedance
in the wires and plugs.  good luck, Bruce Roe

[V63]

I might verify a distributor component ground?
A few years the HEI coil ground had a rigid convoluted strap, I have had problems with those.

[The Tassie Devil(le)]

I have a query here.   How does that Ground strap actually get to Ground when the Distributor Cap is a non-conductive material?

Or, is there a continuation of that screw to the distributor cap hold-down clip so that the continuation goes through the Distributor base, to the engine block?

Or, am I overthinking this?

Bruce.

[TJ Hopland]

In the photo there is a ground label at the top of the right label column.  That is a metal bar that goes to one of the coil mounting bolts.  The connector end is in the harness that goes into the distributor base where its connected to the distributor body.   Its worth checking all that and where that bar goes vs where the ground wire goes. 

Older coils had a copper or brass insert in the bolt holes to make sure you were getting the ground connection.  Now days you never quite know what you are gonna get.  I have had coils where I didn't like the look of how they grounded and ended up cleaning off paint or lacquer sort of material.

[The Tassie Devil(le)]

Thanks for that.   I didn't see the Ground marking that was at the plug, as it blended into the colour of the picture.

Bruce.

[Chopper1942]

You stated that you have good B+ and B- for the dist. How did you check it? If you are doing open circuit testing (connecting B+ lead of DMM to B+ lead and B- lead to ground), you are doing an open circuit test and it only shows the presence of voltage. The proper way to test electrical circuits it to have the load in the circuit on.

1. KOER (key on engine running): check voltage at the battery posts. If a 12 V system with a 10 SI generator, it
   should be approximately 14.4 V.
2. KOER DMM B+ lead on the dist housing and DMM B- lead on the battery post. Should be > 0.5 V. If greater, check the
   grounds between the engine and battery. Voltage drop each cable and connection. Each cable and connection should
   be 0.1 V or less.
3. Back probe the dist B+ terminal with the DMM B+ lead and DMM B- lead on the battery B- post. KOER: the voltage
   should be within 1 V of the battery voltage in step 1. If not, voltage drop the B+ feed from the battery to the
   ignition switch, across the ignition switch, and from the ignition switch to the dist.
4. If all the the wiring and voltage drops check OK, then the dist needs to be addressed.

You need to get a dielectric grease and a dielectric lubricant. They are different. The grease is used on the inside of spark plug boots to prevent arcing. you need to coat the rubber washer in the top of the dist cap on both sides. In the past this was also used under the module. If you can get a small tube of heat sink lube, I would put a generous coating on the bottom of the module.
The dielectric silicone lubricant is used to improve electrical contact and prevent fretting of terminals. Coat the male terminals of the HEI module and the female terminals with a generous coating. Also, do the same for the male electrical terminals in the cap and the female terminals for the dist connector.

["Cadillac Kid" Greg Surfas 15364]

I would like to repeat my original post. I'm quite familiar with HEI distributors and their components and EVERYTHING on this one is correct

Well it seems to be happening to me too. I'm just getting a few thousand miles on ignition modules. Connections are good, coil, cap and rotor are good (DUI), and the ground is a full size battery cable from the negative post of the battery to the front of the block. Anyone have any suggestions THAT CURED THEM OF THE SAME ISSUE?

[Cadman-iac]

Greg,

You didn't mention how old or new the modules are that you are having problems with. Are they original units with mileage on them, or NOS, good used GM units, or new ones from our cheap-ass friends from overseas?

 One thing that I have noticed when I had problems blowing modules in my 81 El Camino was the body to engine ground wire not having a good connection at the firewall. Once I replaced the screw with a slightly larger one I had no more issues with the modules. Before I found the loose connection, I had blown 2 modules, both GM units too.

  Rick

["Cadillac Kid" Greg Surfas 15364]

Rick, I don't know how the body to engine ground would cause the short lived modules (6 mos to one year, Genuine GM, DUI Delphi, etc.) but it is something I will check if it worked for you.
Greg Surfas

[Chopper1942]

Yah, I know some only want the "Silver Bullet" that will "fix" the issue without having to do any testing. I have an HEI with the OE module that has 210K miles on it. Every 30-40K I pull the distributor and clean, lubricate, and check the electrical circuits. This HEI has an ACCEL high output coil and I use mag wires so I don't have to worry about cracks in the graphite cores of OE wire, which causes higher required output of the coil to bridge the gaps. Higher sustained output and/or lower primary winding resistance in the coil causes higher amperage flow through the module, which in-turn causes module failure.

Since most of you don't have an oscilloscope with a fast enough capture rate to see it, I didn't go into it, but bcroe mentioned it and that is voltage spikes. AC clutches, blower relays, or anything that has a winding can cause a voltage spike when turned off and the magnetic field collaspes, I have seen spikes on a 12 V system exceed 150 V. These can and will cause damage to electrical components in a vehicle.

[TJ Hopland]

Yes spikes are worth investigating. Don't ignore the secondary side (coil,cap,rotor, wires, plugs) either especially if none of that has changed with all the failed modules.  An issue with those could be causing too high a voltage going to the wrong place.  If you have changed most or all of that stuff then its less likely to be the issue.

I was asking about the primary side measuring at the cap because I have seen issues like nice paint effecting the ground and original wiring like bulkhead connectors and resistor wires lower the voltage which means higher current which could be too much for the module to handle.  If its low enough its also possible for the module to sort of loose its mind and do things it should not do like stick on which will also kill em.  You need to wire up a meter to test it under load like on the highway.  Idle can read fine but you put more load on for an extended period and resistance heats up and makes things worse.

I'm not as active in as many forums as I once was so maybe things have changed but Davis would be a place I would have considered getting a module from if I needed one.  For those that don't know them their whole thing was making HEI distributors for other makes.  They have been doing it for at least 30 years.  You name it they probably made one so their main product needs a good module so if anyone was going to try and source the best that is available I would trust them to do it over pretty much any other big brand where a module is barely a single line item on a spreadsheet.         

[dplotkin]

Greg:
The HEI module switches primary current to the coil. Users of conventional ignition using points or substitutes such as "Pertronix" often run into coil failures when coil primary resistance is not matched to the ballast resistor or resistor wire. And the Pertronix unit itself often fails when the wrong coil is used or it is miswired.

In either case excessive primary current appears to be burning out your HEI module. So I would verify that the module you are using and the coil are happy together.

Danny Plotkin
By no means an expert.

["Cadillac Kid" Greg Surfas 15364]

Danny,
DUI coil, module, cap, rotor and pick-up.
Greg Surfas

[The Tassie Devil(le)]

I had an experience of my own HEI letting me down.   This was a GM HEI I installed in my '72 500.

Car ran well, then the next morning, it refused to start.   Called the RACT (your AAA) as I was away from home, and after loosening the module, and re-screwing it back, everything worked, and still does, years later.

Why it stopped?   Still don't know to this day, but, now I do carry a spare.

Bruce.

[Cadman-iac]

Rick, I don't know how the body to engine ground would cause the short lived modules (6 mos to one year, Genuine GM, DUI Delphi, etc.) but it is something I will check if it worked for you.
Greg Surfas

 I could never figure out exactly how that would make a difference either, but after replacing the screw on the ground strap making it tight, the problem went away. It may have been just a coincidence, I don't know, but I figured I'd throw it out there.

 Rick

["Cadillac Kid" Greg Surfas 15364]

Welllll, went back to check the body/engine ground strap and guess what? Apparently a couple of years ago (when this issue started) I forgot to reinstall that strap when I did the engine. Thanks Rick for the suggestion.
To everyone kind enough to respond I should have started with a complete list of everything I have already done and I apologize, so here it is.
1. checked grounds from coil to dist. housing, dist housing to engine, engine to ground cable.
2. checked to verify the diode in the "generator" light circuit was correct.
3. Verified coil windings.
4. noted that the capacitor is justto eliminate radio interference.
5. 0 voltage to HEI with key off
6. 12-13.2 volts to HEI under operation.
7. overheated module will melt the heat transfer paste and it appears un effected.
I'm sure I checked other things but never thought about the engine/body ground strap.So thanks again Rick and we will see what happens. I too carry a spare module with me
Greg Surfas