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Old 02-17-2012, 04:20 PM
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please help....keep frying ignition mods

greetings all,
I'm a new member here and could use some help. I have a 1981 chevy truck C-10 that had an inline 6 engine originally. I pulled it and dropped in a 350. Ever since I did this I've had to replace a fried ignition module about every 6 months. Originally the 350 had a Mallory Unilite dist. After changing the module in that about 5 times over 2 years, I put in a HEI dist. Same problem. I rebuilt the entire dist and same problem. New plugs, wires, rotor, cap, coil.....same problem. I have tried ground wires right to the module itself....same problem. The only thing that is common to the 2 distributors is the alternator and starter. I have 11.5 volts not running and 14.4 when running. Could the starter be throwing a voltage spike when starting? It's a high torque starter. I'm about ready to put in an after market voltage regulator to see if that fixes it.
About ready to sell the dam thing......

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Old 02-17-2012, 06:03 PM
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Do you have a Internal voltage regulator (in the Alt) or external (bolted to the fire wall).

Are you using the original resistance wire from the ing switch or did you run a new wire that is hot in start and run positions on the ing switch
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Old 02-17-2012, 06:11 PM
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It could be possible that your alternator is voltage spiking on occasion.
I had an old chevy van that started to do that, I was on my way home one night and the headlights got REAL bright, then went to normal, then all of a sudden went REAL BRIGHT again and stayed there. I went home promptly and changed it the alternator. Point is... If it were daytime I may not have noticed , it had gauges too, but I usually dont look at them often enough. Traffic keeps me busy there. GM modules can take quite a bit of overvoltage and IIRC they will shutoff to protect themselves, aftermarket modules dont allways have functions like those, and overvoltages can fry them. Just a thought.
A stray high voltage arc will kill most any module, even a GM. I had a pickup come in that was TBI. it had quit running and I suspected the module after looking at it.So I had a good used one that I kept for testing purposes and put it in. The truck started, ran for a minute backfired and died. Seems the coil was bad also, it still made good spark , but leaked the high voltage to the primary side and killed my module.Key point is that I replaced the coil AND the module with a new one to cover my bunns.
Not to sure what to tell you to try here, but maybe some of this will give you direction.
I would start by putting a good voltmeter on it and watching it for signs of trouble.
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Old 02-18-2012, 02:00 PM
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Quote:
Originally Posted by spiffy61
greetings all,
I'm a new member here and could use some help. I have a 1981 chevy truck C-10 that had an inline 6 engine originally. I pulled it and dropped in a 350. Ever since I did this I've had to replace a fried ignition module about every 6 months. Originally the 350 had a Mallory Unilite dist. After changing the module in that about 5 times over 2 years, I put in a HEI dist. Same problem. I rebuilt the entire dist and same problem. New plugs, wires, rotor, cap, coil.....same problem. I have tried ground wires right to the module itself....same problem. The only thing that is common to the 2 distributors is the alternator and starter. I have 11.5 volts not running and 14.4 when running. Could the starter be throwing a voltage spike when starting? It's a high torque starter. I'm about ready to put in an after market voltage regulator to see if that fixes it.
About ready to sell the dam thing......
The voltages you quoted, are those at the distributor or at the battery.
I would also check your engine ground to make sure it is clean and tight.
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Old 02-18-2012, 04:10 PM
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modules..

Thanks for the responses!! great stuff.
I'm using the original ign wire (its pink). I don't know if it's a resistance wire. Whats the voltage supposed to be on the pink wire? Should it change from START to RUN? Those voltages are at the distributor(pink wire). The 14.4 V is at idle. All grounds are clean and tight. I'm using the regulator that's in the alternator (I assume it has one). I am going to hook up a digital voltmeter and watch it while I am driving. That should tell me if the "running down the highway voltage" is too high.
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Old 02-18-2012, 07:50 PM
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Quote:
Originally Posted by spiffy61
Thanks for the responses!! great stuff.
I'm using the original ign wire (its pink). I don't know if it's a resistance wire. Whats the voltage supposed to be on the pink wire? Should it change from START to RUN? Those voltages are at the distributor(pink wire). The 14.4 V is at idle. All grounds are clean and tight. I'm using the regulator that's in the alternator (I assume it has one). I am going to hook up a digital voltmeter and watch it while I am driving. That should tell me if the "running down the highway voltage" is too high.
Actually in most case low voltage will be worse than high. Low voltage raises the current and creates more heat. The battery provides a pretty good cushion against spikes so I really don't think that is your issue.
Your voltage at the distributor sounds fine.
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Old 02-18-2012, 09:06 PM
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Do you have an external regulator.... located next to the horn relay....... reason I ask, mine kept blowin modules till I changed over to a new internal reg, no issues since I did that.

is the terminal connector for the alt oriented

up and down II grey colored plug

or

side by side -- -- white or black colored plug
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Old 02-18-2012, 10:53 PM
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Something different to try. Check the resistance of the ignition coil. It could be bad, or the wrong coil.

Every ignition system boils down to this. There is a transformer, that has a few turns of wire on the primary side, and a lot of turns on the secondary side. The coil positive is hooked up to the battery through a manual switch. There is also a switch, controlled by the engine, or a computer that opens at the time the coil is supposed to fire. This switch could be a set of points, and ignition module, or some integrated circuit buried somewhere else in the engines computer.

If your coil has too low of a resistance, too much current flows. You get a hotter spark, for a while. If you have points, they burn up from switching the high current. If you have a more modern system, the excess current heats semiconductors up too much, and they fail.
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Old 02-19-2012, 09:33 AM
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module...

Thanks guys. Will check for a regulator. I'm only looking for problems not associated with the dist bcuz this is the 2nd dist in the vehicle.
Where can I buy a good aftermarket regulator if I need one?
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Old 02-19-2012, 09:35 AM
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module...

The plug on the alternator is keyed. lol
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Old 02-19-2012, 09:50 AM
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Hei

I have a 350 HEI in a corvette different problem maybe help im not knoking
your rebuild mine was not getting fire to plugs changed coil dist module a guy told me to replace dist it was a acell high perf that did the trick he said
ther is somethings you just cannot explain good luck

Last edited by saltbob; 02-19-2012 at 10:04 AM. Reason: not finished
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Old 02-19-2012, 12:01 PM
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If the battery, and the cables and terminals are in good shape, the battery will damp most voltage spikes.

I still think there is not the proper amount of resistance in the primary ignition circuit. A ballast resistor removed, or a resistance wire swapped out. A coil with too low resistance. something like that.
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Old 02-19-2012, 05:36 PM
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Depending on what type of alt will determine if your alt has an internal regulator. If they are up and down (side by side) like two i's " II " you have an external regulator, if they are left and right (side by side) like two dashes " -- -- " then it is an internal regulator. If you are running an external regulator the best thing you can do is convert it to an internal reg. Very easy to do. Mine was popping modules like popcorn, both GM and Excell, read on the board about doing the swap...... since I did it, haven't had a single issue with the modules. Attached is Doc's version on how to jumper the external regulator..... that's what I used. Finally got around to getting a high end digital cluster and didn’t want to fry it with the old wiring so I re-wired the entire car with a painless kit…… Pretty easy and the absolute best thing I did to the old car.
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Old 02-19-2012, 05:39 PM
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HEI's don't use a ballast resistor or a resistor wire...... straight 12 volts from a switched source.
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Old 02-22-2012, 04:18 PM
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module...

Ok, finally got a new module in and took a bunch of readings with a quality FLUKE meter. These were taken at the distributor. This is an HEI dist in a 350sb 1981 chevy C10.

12.0 V dc not running.
9.5 V dc starting.
13.6 V dc idling.
14.3 V dc @ 50 mph.
.5 VAC @ 50 mph
4KHz @ 50 mph.
------------------------
1.6 Amps dc @ idle
2.6 Amps dc @ 50 mph

The alternator has an internal regulator. The only things i found by the fuse box where the horn relay and a stupid looking thing which i found out was a seat belt buzzer (which I put in the circular file)!
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