Author Topic: Ignition Control Module suggestions  (Read 910 times)

Offline fiddler

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Ignition Control Module suggestions
« on: February 04, 2022, 06:46:34 PM »
I have a 1974 chevy C10 stepside.  The engine is around a 1976 vintage 350.  It has the hei ignition.  I lost spark today.  I had a load of wood on the truck and was heading 8 miles home when it died at a stop sign.  Then it died momentarily on the freeway, but fired right back up.  It kept kachunking up the last mile of hill getting to the house.  When I got to the driveway it died 3 times while trying to position the truck to unload the wood.  Now I have unloaded the wood and the ignition is totally non existent.  I think my truck loves me.   It waited to get home and the job done before it laid down....   That being said...I have a hot accel racing coil and wires on the rig just to ensure I got plenty of spark.  I understand that the hot coil may be taking ignition modules.  I don't race the truck and I was looking for reliability when installed that coil.  Does anybody know 1) Do the hot coils in fact take out ignition control modules and 2) Is there a particular brand I should be looking for to get better reliability?  So far the rest the components check good so I am pretty sure the ICM is gone again.  This one lasted maybe 8000 miles....   I will go for parts tomorrow but may order them depending on response from you guys.  I am also going to replace the coil with a standard stock level unit.  Thanks much
Ricky

Online Rapid Roy

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Re: Ignition Control Module suggestions
« Reply #1 on: February 04, 2022, 09:52:21 PM »
If it has the GM ACDelco HEI, replace with same parts. I had issues with the aftermarket modules until I replaced with the AC Delco parts.
1974 Cheyenne 10 LWB STOCK 350 W HEI /TH350/AC/4 BBL Quadrajet
Mopar by Birth
Chevy by Choice

Offline bd

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Re: Ignition Control Module suggestions
« Reply #2 on: February 05, 2022, 10:21:57 AM »
The issue with high output ignition coils is the increased current demand placed on the switching module.  There is nothing wrong with installing a high-output coil as long as you install a higher current capacity module at the same time.  Consider using a Pertronix Flamethrower III module or MSD module with your Accel coil.  Personally, I would upgrade the entire distributor with a billet MSD plus MSD digital box or leave the ignition completely stock.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline fiddler

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Re: Ignition Control Module suggestions
« Reply #3 on: February 05, 2022, 02:12:37 PM »
So at this point the quick fix is to try the pertronix or msd module.  In my heart I want to keep the high output coil.  It just feels better to have hotter spark.  The old girl starts and drives like a new truck most of the time so I want to not mess with what I have.   If I lose the new module as well I will go back to stock at that time.  Once more into the breech!!  Thanks for your inputs.  Always helps to share experience.
Ricky

Offline VileZambonie

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Re: Ignition Control Module suggestions
« Reply #4 on: February 05, 2022, 02:23:56 PM »
If you are running a high output coil, you also need to run the matching carbon button, cap and rotor. You will melt a hole right in that bad boy. My advice is run a stock, readily available to you unit. When you are ready, update the entire ignition system.
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Offline fiddler

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Re: Ignition Control Module suggestions
« Reply #5 on: February 06, 2022, 11:56:23 PM »
The coil, cap and rotor all came as one unit so they are matched.  I thought I had all my bases covered, but did not know about the ICM.   Thanks again all.  I am supposed to receive the pertronix flamethrower III tomorrow.   
Ricky

Offline TexasRed

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Re: Ignition Control Module suggestions
« Reply #6 on: February 07, 2022, 09:58:14 PM »
The high output coils sometimes take out the module when they fail. They may "test" on the ohm-meter just fine when cold but if taken up to temperature they layer short. Epoxy, that you and I can afford, HOLDS in heat. The best are the oil filled coils like the transformers you see on the electrical poles, but those are external from the cap. You'd need to do some wiring and build your own adapter to get it to work with HEI.

There is a guy floating around internet boards that explains it better than I can, IgnitionMan, or Dave Ray. If you google him, you can see some of his explanations of the problems with the HEI coil. He's been banned from a lot of forums, so you'll see that too. Doesn't make him wrong about the coil however.

The only thing I've ever really seen about the button is that high resistance ones CAN cause melting in the cap. Normally there's like a 5k ohms resistance button in a lot of cap and rotor kits, but MSD sells a low resistance one at 1k. The other pieces are usually brass and aluminum. I didn't measure a difference between the button in either one of those materials from Borg Warner's kits (both 5k), but I have heard the lower priced ones come with the low resistance already.

Those "high voltage" coils may deliver high voltage when they are cold but they drop off when they are hot. Plus they usually only deliver what is required to fire the plug, which may not be as much as you'd think.

My advice is if you want to keep the coil in cap is go stock style on the coil and module. The modules are VERY similar. There is supposedly a slight difference in the 996 modules, which the NAPA one is supposed to be a copy of, but you should always try to test the module before you leave the store.

The other thing to check is your grounds. A lot of these rigs have old rusty grounds and that can kill modules in a hurry too.

Offline VileZambonie

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Re: Ignition Control Module suggestions
« Reply #7 on: February 08, 2022, 07:45:07 AM »
I agree on the bad grounds being a majorly overlooked issue.  This
Quote
but you should always try to test the module before you leave the store
won't do much of anything other than potentially wreck a new module. To your point about temperature affecting the dynamic operation of the coil, the same goes for the module which is an ESD sensitive component. Letting some parts jockey potentially send a lightning bolt through a new module is generally a bad idea. They are tested before they're boxed, so re-retesting by an incompetent is asking for trouble.
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Offline fiddler

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Re: Ignition Control Module suggestions
« Reply #8 on: February 10, 2022, 07:22:02 PM »
Thanks for your help guys!  OK so now I am in serious debug mode.  I stuck in a pertroinix ICM and it lasted 5 miles.  Thinking infant mortality I stuck in the msd ICM that i bought as a spare.  It lasted to about half way down the driveway.  Mind you I have an 800 foot driveway that goes down a hill, has hill and trees on either side, and is only 10 feet to 12 feet wide.  So now the truck is blocking the driveway and i cant get the car out for parts.  I live 12 miles from the nearest parts place and no transportation out here.  So...I had the AC Delco ICM that I bought as a backup after the pertronix "failed" (Not Pertronix fault I think).  I stuck that in and got the truck back to its parking place.  NOW I will be replacing the coil, cap, rotor, condenser (you would think we could call them capacitors now, condenser in electronics went out way at the beginning of tubes),  Stock parts, and a new AC DELCO ICM.  Now...to the grounds....I have tested all grounds and they are lead resistance back to the battery..  About point one two ohms.  I verified the voltage to the distributor and it is about .2 volts less than the battery to the negative battery terminal so that is good.  I suspect the coil may have an issue that I can't see with a DVM.  They are so hard to test without a hi pot.....  I will just have to throw money at it....
Ricky

Offline TexasRed

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Re: Ignition Control Module suggestions
« Reply #9 on: February 10, 2022, 08:01:43 PM »
The "condenser" I think is to limit radio interference.

I would inspect the cap and rotor before replacement. Just stock style module and coil . . . .if it were me and I wanted to keep the coil in cap.

One single copper strand would probably show almost zero resistance, but when you're starting and running the ignition, it can pull a lot of juice. I would make sure there are clean connections on both the battery and where it connects to the engine.

I suspect it's the "super-duper" coil that failed and took out the module.

Offline bd

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Re: Ignition Control Module suggestions
« Reply #10 on: February 11, 2022, 09:49:12 AM »
The coil could be the culprit, but there are other things to consider.

Have you verified that the HEI coil ground strap is in place (attached images)?

Then, what convinced you that all of those modules are actually bad?  Have you swapped one or more of the "bad" modules back into the distributor to see if it will fire, even for a short time?  What about the pickup coil (PUC)?  PUC failures are known to be intermittent and difficult to positively diagnose without a DMM and oscilloscope when not hard failures.  See, Distributor components testing.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline fiddler

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Re: Ignition Control Module suggestions
« Reply #11 on: February 11, 2022, 11:06:11 AM »
So l have decided just to replace the distributor.  By the time I got the stock coil and cap and rotor and cap cover and ICM I am looking at the price of a new distributor.  Anybody got a favorite distributor to recommend??
Ricky

Offline fiddler

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Re: Ignition Control Module suggestions
« Reply #12 on: February 11, 2022, 01:49:14 PM »
Rereading my replies here I do have one recommendation for an MSD distributor.  I can't find a NEW AC DELCO so I am thinking a new MSD is going to last longer than a re-manufactured AC Delco.  Thoughts?
Ricky

Offline VileZambonie

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Re: Ignition Control Module suggestions
« Reply #13 on: February 12, 2022, 06:56:37 AM »
Sounds like your truck is sitting still over a bad pickup coil and you are blaming the module for it. Get one of those eBay special HEI's to stab in there and get back on the road again. Save up for a nice ignition system upgrade like an MSD.
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74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline fiddler

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Re: Ignition Control Module suggestions
« Reply #14 on: February 12, 2022, 11:57:24 PM »
VileZambonie, I do not need to save up for an MSD ignition system, but I would like to know the ins and outs of what to get.  There are a lot of MSD ignition systems out there.  I don't need a racing system as I just use the truck to go to town for things that won't fit in the car, and I drive it to fiddle practice once a week so my wife isn't stuck without the car if she needs it.  Maybe a trip to the dump once in while, pick up firewood, etc etc.  I am looking for reliability.  Also I like to do the wrenching now that I am retired and don't have to make it go today.  So it would be cheap and "fun" to go ahead and try a pickup module.  I have not tried putting one of the suspected bad ICMs back in the truck.  I had a plate full of things to do today.  The sun is shining and if that pasture gets ahead of me mowing it will be a nightmare.  Best to keep it short before it becomes a fire danger.....  Anyway, so you think an MSD unit would be a good upgrade?  Any suggestions as to which one?   
Ricky