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Discussion Starter #1
Hello Everyone,

I'm pulling my hair out at the moment. My 65 mustang seems to have an electrical issue that I can't figure out. I will be driving down the road perfectly normal, and the car will shut off. All accessories still stay on, the ALT light kicks on, but the motor very suddenly dies. Just as if you turned the key and shut it off. No misfire, no sputtering, etc. When I turn the key back into start, and it fires right up like nothing happened. Every time. From what I've noticed it isn't doing it when I hit a bump. It actually has done it a few times idling in my driveway.

I've replaced the ignition switch. I've removed my battery cutoff on the negative battery lead. I've tested the battery, alternator, and coil voltages and all seems fine. I've also rooted around under the dash wiggling ignition wires as well as the resistance wire going to the coil while idling and I can't get it to shut off.

I've heard that unilite modules have a tendency to fail. That said, I just want to try everything else before I spend $80 on a part. I'm going to test the module tonight with a volt meter using the testing procedure in the manual but I'm afraid I won't see anything because the issue is so intermittent.

Any ideas? Full car setup is below.

Car / Engine:
65 mustang, 331 stroker, C4 Transmission, Mild "street" cam (not sure of exact specs, but definitely not a stock cam), Edelbrock RPM heads, Performer 289 intake , Holley 4160 carb (rebuilt), Mallory unlilite distributor, Accel Super Stock Coil, 8mm Wires, Autolite 3924 spark plugs (.04 gap), Timing: 13 Degrees initial about 36 degrees total @ 3500rpm, No Vacuum advance (it has never had it since I've owned the car, and the motor runs really bad with both ported and manifold vacuum), Manual Steering, Manual brakes
 

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I would check for power to the coil with the key in the run position. Sounds like you have power to the coil when in cranking mode but not in the run mode.
 

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The engine shutting off suddenly when you hit a bump sounds like a wire either losing it's connection or shorting out. Since everything else still has power I'd say it's a wire in the ignition system.
 

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Could very well be a problem with one of the main battery cables too. Grounds (down on the block) frequently corrode in a not-so-visible way. They will flow power just fine a lot of the time, and then not.


I am wondering if it's not your ignition module.
 

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The engine shutting off suddenly when you hit a bump sounds like a wire either losing it's connection or shorting out. Since everything else still has power I'd say it's a wire in the ignition system.
The poster noted "isn't" doing it when I hit a bump". From this it's a little deeper?
 

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I'm thinking, as mentioned, a sudden cutting out, is an indication of an ignition electrical supply issue. How about, check inside the distributor to insure there are no ground or electrical faults there, among others. Then, go back from there.
 
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I am also running a Mallory Unilite distributor in my 331. Last year I had an almost identical problem. The engine would suddenly cut out. No spluttering, just suddenly stone dead! This was happening very sporadically at first. The engine would start immediately as if nothing was wrong. Because this was very sporadic I connected a voltmeter with extra long leads to the ballast resistor & had the volt meter in the car. I went for a drive & after about 3 miles you guessed it the engine cut out. The voltmeter still showed 12.8 Volts. So I quickly opened the hood & connected my spark tester between the coil HT cable & the distributor cap. Cranked the starter & no spark. I waited maybe 30 seconds & cranked again. The engine fired right up as if nothing had ever been wrong. Hmm. After checking all the ignition wiring for what felt like the 100th time I decided to buy a new distributor module. Since installing it last year the engine has not cut out again. Maybe you have the same problem.
 

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That's a text book example of electronics failure from heat. Once it cools down it works fine until it heats back up. Replace the ignition module.

Many years ago my dad had a 77 Granada with a 302. While you don't have a Duraspark system, my dad's car did the same until we replaced the module.
 

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Discussion Starter #9
I am also running a Mallory Unilite distributor in my 331. Last year I had an almost identical problem. The engine would suddenly cut out. No spluttering, just suddenly stone dead! This was happening very sporadically at first. The engine would start immediately as if nothing was wrong. Because this was very sporadic I connected a voltmeter with extra long leads to the ballast resistor & had the volt meter in the car. I went for a drive & after about 3 miles you guessed it the engine cut out. The voltmeter still showed 12.8 Volts. So I quickly opened the hood & connected my spark tester between the coil HT cable & the distributor cap. Cranked the starter & no spark. I waited maybe 30 seconds & cranked again. The engine fired right up as if nothing had ever been wrong. Hmm. After checking all the ignition wiring for what felt like the 100th time I decided to buy a new distributor module. Since installing it last year the engine has not cut out again. Maybe you have the same problem.

Thanks for this reply.

I went ahead and bit the bullet. Ordered a new module and it'll be in tomorrow. will report back.
 

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Dont forget to apply a smear of thermal conductive grease to the underside of the module where it sits on the distributor base plate. It's normally a white grease that insulates the module from some of the heat on the baseplate.
Oh BTW. I have my distributor vacuum advance hooked up to full manifold vacuum. Sweet as a nut.
 

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A thermal conductive grease is actually designed to enhance the transfer of heat. This is done to more efficiently move the heat from one area to another such as from an electrical component into it's heat sink.
 
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