HEI control module - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**MJN** · 06-02-2002, 07:57 AM

I have been having trouble keeping control modules in my '72 Blazer. We just put in a brand new distributor about 7 or 8 months ago and I had to put a new module in before school. We went through two of them with the old distributor also. What could be going on? Too much heat or vibration? It seems like they slowly get weaker and weaker then it doesn't start one day. Anyone else have this problem? The next time it does this I'm going back to points!

bobs409 · 06-02-2002, 08:06 AM

I know what you mean, im not into "electronic" much myself. 5 of 6 of my vehicles have points. LOL Make sure you carry a spare module and tools to replace because as you probably know, when they go, they're gone.

2 things that come to mind that may cause problems are;

Did you put the special grease on the metal side of the module that helps disipate heat? If not, heat may be doing it.

I would also check the voltage going to the coil. Check to be sure your not overcharging.

71GMC_3/4T · 06-02-2002, 10:08 AM

You might want to try one from Chevy garage, or a high dollar one from Napa.
There must be a reason the ones from checker and autozone are dirt cheap...

**MikeB** · 06-02-2002, 10:24 AM

Spend the bucks and get an P/N 8364 HEI module from MSD. It will output more current to your coil and will last forever. At a later date you can also get their HEI coil. http://www.msdignition.com/

Cost is around $68 at Summit Racing.

*Zkast* · 06-02-2002, 11:22 AM

There are a few things that will "knock" a module out.

Voltage - If your running over 17v for extended periods of time it will overheat and burn.

Pick-up coil - If the coil is bad it will send ac voltage spikes to the module and kill it. The module is normaly switched with a ac signal from the coil but after age/time the coil will start to send irratic signals acting more like a capacitor.

Bad ignition Coil - If the primary windings in the coil have to high of a resistance it requires to high of a load in the module which will burn the module out after time.

The easiest thing to check is the coil (most probable). If you need a schematic and values let me know and I'll post them. Most cheap manuals show how to test for a bad coil though.

Oh and the most important thing... Buy good quality modules. Standard, Borg-warner, AC Delco or MSD have good aftermarket modules. If your using WELLS ignition parts you can start by replaceing that first LOL.

Good luck with it.

06-02-2002, 07:57 AM	#1
MJN Registered User Join Date: Feb 2000 Location: Maquoketa, Ia/ Orr, Mn Posts: 3,051	HEI control module I have been having trouble keeping control modules in my '72 Blazer. We just put in a brand new distributor about 7 or 8 months ago and I had to put a new module in before school. We went through two of them with the old distributor also. What could be going on? Too much heat or vibration? It seems like they slowly get weaker and weaker then it doesn't start one day. Anyone else have this problem? The next time it does this I'm going back to points!

06-02-2002, 08:06 AM	#2
bobs409 1969 Custom 30 wrecker Join Date: Sep 2001 Location: Pottsville, Pa Posts: 2,611	I know what you mean, im not into "electronic" much myself. 5 of 6 of my vehicles have points. LOL Make sure you carry a spare module and tools to replace because as you probably know, when they go, they're gone. 2 things that come to mind that may cause problems are; Did you put the special grease on the metal side of the module that helps disipate heat? If not, heat may be doing it. I would also check the voltage going to the coil. Check to be sure your not overcharging. __________________ Bob 63 Impala 283/PG/3.36 (under restoration) 66 Impala 327/PG/3.36 66 Chevelle SS 409/M22/3.55 69 Chevelle 307/PG/3.08 (future restoration) 69 C10 short stepside 454/TH350/3.73 69 Custom 30 tow truck 350/4 spd/4.10 (resto done, CRUISIN TIME!) 71 Cheyenne 20 fleetside 350/4 spd/4.10 71 Chevelle 6/PG/3.08 72 Chevelle 454/M21/4.10

06-02-2002, 10:08 AM	#3
71GMC_3/4T Weapons Of Construction Join Date: Apr 2000 Location: Colorado, USA Posts: 1,095	You might want to try one from Chevy garage, or a high dollar one from Napa. There must be a reason the ones from checker and autozone are dirt cheap... __________________ 1971 GMC 2500, 402/TH400 4.10 Daily Driver Lafayette, CO

06-02-2002, 10:24 AM	#4
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,597	Spend the bucks and get an P/N 8364 HEI module from MSD. It will output more current to your coil and will last forever. At a later date you can also get their HEI coil. http://www.msdignition.com/ Cost is around $68 at Summit Racing. __________________ Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, recent AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then!

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06-02-2002, 11:22 AM	#5
Zkast Account Suspended Join Date: May 2002 Location: Olathe, Kansas Posts: 929	There are a few things that will "knock" a module out. Voltage - If your running over 17v for extended periods of time it will overheat and burn. Pick-up coil - If the coil is bad it will send ac voltage spikes to the module and kill it. The module is normaly switched with a ac signal from the coil but after age/time the coil will start to send irratic signals acting more like a capacitor. Bad ignition Coil - If the primary windings in the coil have to high of a resistance it requires to high of a load in the module which will burn the module out after time. The easiest thing to check is the coil (most probable). If you need a schematic and values let me know and I'll post them. Most cheap manuals show how to test for a bad coil though. Oh and the most important thing... Buy good quality modules. Standard, Borg-warner, AC Delco or MSD have good aftermarket modules. If your using WELLS ignition parts you can start by replaceing that first LOL. Good luck with it.



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