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Discussion Starter #1
’69, base coupe, not original 350, MSD Streetfire HEI distributor installed two springs ago. Both under hood wiring harnesses brand new and main under dash harness replaced with excellent condition used harness two years ago. New starter two years ago. New alternator last spring. Last spring I put a rebuilt Quadrajet on it. The mechanic that rebuilt it gave it an initial adjustment so it ran ok but if you jump on it, it hesitates. I haven’t had the cash to get it back to him for the final fine tuning and choke adjustment but I’ve been driving it at least four months with no problems. It does run warm on these warm summer days but it’s always been like that.

So a week ago I pull in my driveway after coming home from work and it dies, turns over but won’t start, seems like no spark. I crack the gas cap in case it might be vapor locked, didn’t help. Let it set for several hours and it started and ran like usual. I’m still not sure what was up so I don’t take it far, just run around town in it, I did this for a few days. One evening, after running around town a little so it was up to temp it just died as I was rolling down the street, maybe 10-15 mph. I get it home, but this time it won’t start even after a day or two. I test for spark and as far as I can tell, I’m a rookie, it doesn’t seem to be getting any. I pull the ignition module and coil from the distributor and have Autozone test them, they tested out ok. There is a slight amount of corrosion on the contact point inside the dist. so I clean that up, put a fresh layer of heat sink silicone on the bottom of the module, put everything back together, it starts and runs like it always has. Once again I run it around town, even take a few longer rides, 20 +/- minutes, runs fine. So this morning I take it to work, about a 15 minute drive, as I roll into the parking lot it dies, turns over but won’t pop. I tried after letting it sit an hour, still, no pop.

Could an ignition module fail intermittently? If it was going bad wouldn’t it fail every time it got hot?

Suggestions?
 

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I have had a module in a unilite dist. fail as you describe.
 

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This sounds like the classic loose battery to fender ground wire issue. Check that cable. Make sure it is tight. Make sure the star washer is making good metal to metal contact. If good, check every ignition related wire and its connection
 

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Discussion Starter #5
Jon, I know this is lame, but I can't even remember where battery to fender ground is from when I rewired things. If it was a loose ground wouldn't that maybe give you issues, say when you like bounced over some train tracks or rough road? Would it be fine one moment then not the next, then change on its own in anywhere from several hours to several days?
I'm not trying to be difficult, it's just that this is all fairly new to me so I'm trying to understand things from all angles, ask questions, increase my understanding.
Thanks.
 

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since you think it's spark next time it won't start test the voltage at the MSD. That way you can eliminate a power issue vs the module. If you have power then I'd test the ground. If both are there you have a bad module.
 

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Discussion Starter #7
since you think it's spark next time it won't start test the voltage at the MSD. That way you can eliminate a power issue vs the module. If you have power then I'd test the ground. If both are there you have a bad module.
Thanks. Now since this is all new to me, it should have power to the MSD with the key in the run postion regardless of whether it's actually running, right? So turn the key to run, then use a voltmeter and measure the volts going into the MSD from the battery?
 

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Yes, it should be energized with the key in the On position. Make sure you check the ground as well as the hot. unfortunately you'll have to wait until it dies on you to do it.
 

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Thanks. Now since this is all new to me, it should have power to the MSD with the key in the run postion regardless of whether it's actually running, right? So turn the key to run, then use a voltmeter and measure the volts going into the MSD from the battery?
Yes. It should show a full 12 volts. That is what an HEI needs. As far as the ground wire, it is a black wire leading directly going to and attaching to the inside edge of the actual fender. Can't miss it. And yes, it can be that random.
 

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Discussion Starter #11
Yes. It should show a full 12 volts. That is what an HEI needs. As far as the ground wire, it is a black wire leading directly going to and attaching to the inside edge of the actual fender. Can't miss it. And yes, it can be that random.
This wiring was such a cluster you know what when I got it that I had to replace both underdash harnesses. There was no fender ground before that I recall, but I also recall thinking that I grounded one out when I rewired it, I just don't remember where. Gonna have to do some looking around after I drag it home.
 

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Discussion Starter #13
since you think it's spark next time it won't start test the voltage at the MSD. That way you can eliminate a power issue vs the module. If you have power then I'd test the ground. If both are there you have a bad module.
They say there's no such thing as a stupid question so I hope this isn't one, but when you say test the ground, is there a ground on the MSD or are you referring to the ground Jon was talking about? I'm not at the car but as I recall there are the wires coming from the module and the battery wire and the tach wire but I don't remember a grounding wire. Am I off base?
 

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The ground wire location will be at the battery area. There should be a smaller cable attached to your black ground cable that goes to your battery. It would then go over toward the passenger side fender and close to the battery and fasten to the inside of the fender lip with a bolt. The other end of the main ground cable should run from battery to engine for a good ground. There are also the firewall ground areas that you should check. Hope this helped.
J.R.
 

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Discussion Starter #15
I'm looking and I'm honestly not seeing a smaller battery ground. I remember when I rewired it not finding one then, apparently I didn't hook one up then. It ran like that all last summer and all of this summer.

I checked the power going into the MSD, 12 volts, but when I crank it no pop. So maybe it's looking like the module?

A module at Autozone is around 48 bucks. A coil is 49. You can buy a Proform tune up kit for 82 and includes High-power 50,000 Volts HEI coil. Superior "no arc" rotor. Coil dust cover. High-performance. Low-saturation control module. Adjustable vacuum advance unit. HEI bushing. Wire harness and capacitor. High performance advance spring and weight set. Mounting hardware.
If it's any good wouldn't it make sense to replace everything?
 

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First off, GROUNDING from battery goes to the ENGINE FIRST, via the large gauge cable, then, the chassis, from engine to chassis, or by the small gauge wire form the battery terminal to the core support, horn relay mounting bracket, etc, NOT battery to chassis to engine.

One of two issues with coil in cap HEI,

The coil is layer shorting, which will cause module failure (for no apparent reason) as it is failing.

the two wires from the magnetic pickup to the module are fragmented/broken at the module connector, and it can be tested by checking for spark while applying vacuum to the vacuum advance unit as the engine is being spun over. This moves the wires at the connector, and might show connect.disconnect. The correct fix for this is to replace the ENTIRE magnetic pickup as an assembled unit, NOT just changing the coil inside it.

HEI module failures can also be enhanced by not installing the carbon brush correctly, allowing for a gap between the brush and rotor bar, and/or running spark plug gaps over .045, as .045 IS MAX GAP for them. In the 1980's, GM tried both .060 and .080 spark plug gaps with the coil in cap HEI's, and had massive module/coil failures form the excessive voltage, with NO increase in spark ou8tput levels that helped anything. Doing nothing more than dropping the plug gaps down to .045 stopped the module/coil failures.

All the horse hockie of "special tune up kits with billion volt coils" is just that, hockie, save your money. Stock caps, rotors coils magnetic pickups and modules work the best, and, NO HEI will make any more volts when it gets ALL THE WAY UP TO OPERATING TEMPERATURES, then another, which is in the low to middle of the 10,000 to 20,000 volt level, NONE.

Mallory Uni-Lite is a fair ignition system, the best of the drop in ones, but, they have a couple of problems.

Some facilities that have NO clue about them, insist they be run on full battery voltage, which causes them to go blind fairly quickly. They MUST be resisted correctly, as they are very happy when run at 6.5 to 9.5 volts, NO HIGHER. This requires TWO ballast resistors, stock GM, and, the one that comes with the Uni-Lite.

The other is that they like stock coils only, and have NO drivers to make any more voltage than a point system makes, NO MATTER THE COIL USED, NOR THE INPUT VOLTAGES FED THEM. Plug gaps down to .032 are good, NO LARGER.
 

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Discussion Starter #17
First off, GROUNDING from battery goes to the ENGINE FIRST, via the large gauge cable, then, the chassis, from engine to chassis, or by the small gauge wire form the battery terminal to the core support, horn relay mounting bracket, etc, NOT battery to chassis to engine.

One of two issues with coil in cap HEI,

The coil is layer shorting, which will cause module failure (for no apparent reason) as it is failing.

the two wires from the magnetic pickup to the module are fragmented/broken at the module connector, and it can be tested by checking for spark while applying vacuum to the vacuum advance unit as the engine is being spun over. This moves the wires at the connector, and might show connect.disconnect. The correct fix for this is to replace the ENTIRE magnetic pickup as an assembled unit, NOT just changing the coil inside it.

HEI module failures can also be enhanced by not installing the carbon brush correctly, allowing for a gap between the brush and rotor bar, and/or running spark plug gaps over .045, as .045 IS MAX GAP for them. In the 1980's, GM tried both .060 and .080 spark plug gaps with the coil in cap HEI's, and had massive module/coil failures form the excessive voltage, with NO increase in spark ou8tput levels that helped anything. Doing nothing more than dropping the plug gaps down to .045 stopped the module/coil failures.

All the horse hockie of "special tune up kits with billion volt coils" is just that, hockie, save your money. Stock caps, rotors coils magnetic pickups and modules work the best, and, NO HEI will make any more volts when it gets ALL THE WAY UP TO OPERATING TEMPERATURES, then another, which is in the low to middle of the 10,000 to 20,000 volt level, NONE.

Mallory Uni-Lite is a fair ignition system, the best of the drop in ones, but, they have a couple of problems.

Some facilities that have NO clue about them, insist they be run on full battery voltage, which causes them to go blind fairly quickly. They MUST be resisted correctly, as they are very happy when run at 6.5 to 9.5 volts, NO HIGHER. This requires TWO ballast resistors, stock GM, and, the one that comes with the Uni-Lite.

The other is that they like stock coils only, and have NO drivers to make any more voltage than a point system makes, NO MATTER THE COIL USED, NOR THE INPUT VOLTAGES FED THEM. Plug gaps down to .032 are good, NO LARGER.
Thanks Dave. Since this is all relatively new to me, where is the magnetic pickup, is it under the centrifugal weight advance? So if I follow you, I likley need to replace the coil, module, and pickup, correct? The cap and rotor look ok. So the "High" powered coils don't really do anything but if that kit comes with the coil, module, cap and rotor for about the same as a coil and module alone would there be anything wrong with using the kit if I was just looking at price per parts and not banking on the extra voltage? or have you found the quality of the Proform parts to be inferior?
 

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Discussion Starter #19
I don't really know how to apply sufficient vacuum to the vacuum advance as Dave suggested. But if I follow him, if I just replace the module or module and coil the new ones will eventually fail if I don't replace the pick up, and if I follow Jon's diagram, I need to pull the dist. and remove the drive gear at the bottom so I can pull the shaft to get to the pick up. Correct?
 

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Discussion Starter #20
So back to Dave, I think I was combining your two points. If I follow you, the coil could be going bad which in turn will ruin the module. OR. The wires from the pick-up coil are breaking. This distributor only has two summers use on it, how likely is it the wires would be breaking with only that much use?
 
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