I'm running a HEI dist. in my SBC. It was new when installed.....probably 10 years ago. I have had to replace the coil twice in the last 4 years. The last time was 2003 when coming back to Md. from Bowling Green (HRR) and most recently when I was coming back from the Cinematic. I always carry spare parts so in went the "used " spare coil and I was on my way. I have been running around on the "spare" coil since. My daily drivers w/ HEI's never give me any problems, so I'm puzzled as to why it is getting persnickety (technical term) in the hot rod. The only thing out of the ordinary is that I am running a MSD module. The last time I had this problem, it was suggested to me that if I was going to run this module that I needed to run a high out put coil. So I put a high output coil in it back in 2004. That's the one that just took a shit on the way back from Ohio. Anyone ever heard of this? Any other suggestions?
I ran a "pieced together" HEI one time. It consisted of a Corvette Mag Impulse dizzy, hooked to a remote HEI module mounted on an aluminum heat sink and lastly connected to a regular Accel Supercoil. The only issue I had was that when I first put it together I ran a "parts store" HEI module - it'd work fine for a month and then crap out. I eventually put in a GM HEI module and it worked perfectly for years. It was my daily driver. What I later learned it that when the aftermarket sells you a replacement part for your car (like a ignition module) they DO NOT sell the same part as GM made. GM owns the circuit design. So the aftermarket comes up with THEIR OWN DESIGN that is supposed to function similarly to what GM (or Ford or Chrysler etc) origionally had. I blew out the aftermarket modules 2 or 3 in a row. My conclusion was that their design was not near as robust as the origional GM stuff. I also concluded that it must have been some slight differences in the Mag Impulse dizzy and an actual GM HEI dizzy that the aftermarket module couldn't deal with for very long. Just something to think about.
I would talk to MSD and see if they have any ideas. Also make sure everything is wired up like it should be. That is where I have always found my problems.
the first thing I would check is supply voltage. HEI will not live very long with less than 12.5 volts or over 15 volts. When we were racing classes that required that we use an HEI we found that if the supply voltage was to high or too low that we had failures with the module and or coil. We always ran an alternator and ran a 10 guage wire to the distributor for supply voltage. We also made sure that there was nothing else on the circuit for the distributor supply. If the spark plug wires have high resistance it will usually burn a hole through the rotor, but I can see where that could also cause the coil to overheat and die. I hope this helps Wesley
If you are running the "normal" HEI plug gap of .060 try closing it down to something like .045 GM later on learned a few things about large gaps and narrowed down their recommendations a bit. Racers were commonly using .045 spark plug gaps with HEI's even before GM changed theirs. Sometimes if you make the gap too big, and the plug wires have a high resistance, and then when the rotor-to-cap-terminal-gap becomes harder to jump (when the sharp edges are eroded to a rounder shape, deposits build up, etc) the total resistance to the spark current becomes high enough, it can encourage the spark current to take an easy way out by arcing internally inside the coil itself. It doesn't take a very high percentage of misfires for the spark to eventually erode an easier path inside the coil. A 3 or 4% misfire rate is probably not enough to ever notice while running but it can eventually eat up a coil from the inside if the spark energy is powerful. IF you are using a big plug gap such as the .060 recommended by GM, you could try a smaller one such as .045 and check the resistance in your plug wires to make sure you don't have a bad one with extra high resistance or somthing along that line... Just one possibility out of many....
The hei is a matched component igntion system like anything else. The coils internal resistance must match the contol module amps and the coil and pick up coil must be of matched polaritys. Also the coil must either run a ground wire or ground plate in the cap. Eating coils ? Then the resistance factor somewhere is incorrect causing high amp draw and there fore a coil failure. I would suspect the replacement coil is too low resistance. Suggested fix replace the module and coil with oem delco parts.
all the above and also check for the ground strap on top of the coil and ground wire out of the cap. it hooks to a bolt holding down the coil and has a terminal next to the tach/power connector on the cap.....must go to a good ground.
Thanks guys. Good stuff here, some I knew and some I didn't. I'm thinking that after making sure all the wireing is OK that I'll just shit can the MSD module and put all new OEM stuff in it. Its not like I'm going through coils every week, but 2 coils in 4 years is a little excessive.........
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