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Unread 09-04-2007, 09:30 PM   #1
Geer_hed
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1977 CJ5 232 Prestolite Ignition mystery

Well this is a bit of a quandary so let me get started....

This is my buddy Scott's 77 CJ5 with good ol prestolite firing away underneath the hood.

One day he calls me up "hey jeep stalled for no apparent reason, I let it cool down, and it started again just fine", so the standard issue - check/replace your ignition module came to mind. It even died one afternoon, and restarted the next morning after he had it towed to a shop, but then died again on him though the shop is less than 5 miles from his house.

Well, the el cheapo replacements from Adv Auto did not do the trick, nor could they actually test either the replacement or the original for him. He was basically screwed. I told him to take it back and try another one, just shot in the dark b/c they couldn't test it, and it also did not work. Chalk one up for my complete lack of faith in replacement modules or the reliability of those distributing them.

I went over there and tried a few things, coil getting current, rotor turning, etc etc etc... all the usuals.... the key here is when I put the testlamp between the coil negative and the ignition module, it did not pulse... it mearly dimmed.... well after a few more measurements and a few beers, I applied the KISS approach and re-installed the last known working component, the old ignition module. Sure enough - the testlamp flashed and the engine cranked over... started and purred like a kitten.

So here's what I know:
  • This is definitely a spark issue
  • the coil, p/u coil, wiring, fuel/air, and all associated demons are not an issue here
  • the ignition module consistently reproduces the single point of failure that is demonstrating his no crank

Another key point here is this: He replaced it with a Prestolite replacement from Napa for nearly $100. It worked for a few cranks and then, nothing... same deal.. no pulse from the module, just a dimming of the testlamp...

Here's what I don't know
  • I didn't have my multimeter, so I'm not sure of the input current to those ignition modules that he has been trying.

My question is this then, given all of that, is there any reason, excluding some strange electrical phenonmenon that allowed his original module to "die" in such a way that it is impervious to the fault that all of these replacement modules are experiencing? The original module is the only one that will start it! Is there something else that those of you that are more experienced with Prestolite can tell me that I might be missing?

Thanks in advance

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Unread 09-05-2007, 06:38 AM   #2
jfwireless
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What about the cable and connector to the ignition module?? Check that ground connection to the igniition module, the case ground and the ground wire on the connector.

Most of us simply replaced the troublesom prestolite with an HEI or other replacement distributor. I ran a mallory unilite for years until I fuel injected.

I do have a couple of good iginition modules in the shop, you are welcome to them if you pick up the shipping. Might also have the wiring and old prestolite distributor if you need them. Just let me know and I will check.

Best advice, just get rid of the Prestolite.

Jim
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Unread 09-05-2007, 08:34 AM   #3
John N
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I don't have a clue, but ....wow....you posted. Welcome back. I think I have some 258 ignition parts you can have, if you want. I know there's a distributor and some other pieces. Price is right...free, just get it out of my shop.
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Unread 09-05-2007, 09:21 AM   #4
Tractor Boy
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I had a DUI dizzy on my 258 that did the same thing. It would run until it got hot and then would die. According to my people, the resistance builds up with heat and therefore, spark goes away. We replaced coil, module and cap with OEM GM parts and Voila, no more problems. The module from O'reilly's didn't last.
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Unread 09-05-2007, 09:29 AM   #5
Geer_hed
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Quote:
Originally Posted by jfwireless
What about the cable and connector to the ignition module?? Check that ground connection to the igniition module, the case ground and the ground wire on the connector.
Ground is good. On a whim, I thought that too and I scraped the fender and the eyehole connector to get good metal, but that wasn't the issue. + it would not explain how 3 other modules crapped out and the old one still works - all of them using the same ground connection!

Quote:
Originally Posted by jfwireless
Most of us simply replaced the troublesom prestolite with an HEI or other replacement distributor. I ran a mallory unilite for years until I fuel injected.
This guy (remember it's not my heep) isn't in to mods at all. He just wants his jeep to run the way it is supposed to with what it rolled off the line with. Crazy huh? The Prestolite would've taken a ride by now for me too, but....

Quote:
Originally Posted by jfwireless
I do have a couple of good iginition modules in the shop, you are welcome to them if you pick up the shipping. Might also have the wiring and old prestolite distributor if you need them. Just let me know and I will check.

Best advice, just get rid of the Prestolite.

Jim
I'll run it by him. He might take you up on your offer. Generous of you, thanks. I'm all duraspark (actually the TFI/HEI, but still same problem), so he and I don't have many interchangeable parts...

Quote:
Originally Posted by JohnN
I don't have a clue, but ....wow....you posted. Welcome back. I think I have some 258 ignition parts you can have, if you want. I know there's a distributor and some other pieces. Price is right...free, just get it out of my shop.
Hey John! yeah long time no post.... A new house and a new wife and a new job will do that to you I guess.... + I'm finding that the first two chew deeply in to the jeep budget. Thanks again for the spare steering gear you lent a while back... I'm guessing you're in the same boat with me on the ignition parts, given your year 8, most likely duraspark, but either way, thanks.... Good guy to know
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Unread 09-05-2007, 09:56 AM   #6
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Have you changed out the bypass capacitor on the positive side of the coil? If this capacitor is bad it may be why you are blowing out ignition modules. This capacitor shunts out high frequency transients coming out of your charging system that can damage the ignition module. Make sure it is still there are good

My prestolite stuff is for a V8, so maybe not good for the 6 cylinder

Jim
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Unread 09-10-2007, 04:06 AM   #7
Geer_hed
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Well go figure...
  1. Module from Advance Auto - dies immediately
  2. Module from Autozone - dies immediate (but still tests good in the store?!? lol)
  3. Module from Autozone - dies after a couple cranks
  4. Module from Napa (Prestolite replacement) - couple of cranks then DEAD
  5. Module from CarQuest (another Prestolite replacement) - works fine

If I could explain it, I would. Whatever... Been driving for days now without issue where the others wouldn't last 10 minutes... we made some adjustments, but nothing that would explain what the heck is going on... Of course now my buddy has the extra module bolted and up and ready to go just in case...

interesting side note, his distributor was making an interesting click. We couldn't figure it out until I nudged the sensor on the pickup coil and it wobbled with ease... it was striking the reluctor wheel on each pass!
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Unread 09-10-2007, 10:15 AM   #8
John Strenk
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Realy, it's time to dump the distributor.
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Unread 09-10-2007, 09:55 PM   #9
Geer_hed
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agreed.... he's just an all original guy I guess... which is funny if you look at the underside of his heep it looks like it's been parked in a lake for a few months... SCARY!!

I'm kind of surprised you didn't have atleast 3 sound theories explaining the phenonmenon within 48 hours of me posting All I could do was shake my head after a while... things like that just get to a point where they just don't add up... oh well, such is a heep...
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Unread 09-14-2007, 10:26 PM   #10
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I've gone through 11 'Premium' modules on one customers vehicle before I yanked the distributor and installed a 'Factory' Motorcraft distributor with harness, coil & module...

Remember, the Prestolite uses a true Hall effect trigger with a full 12 volts running through it.
If the trigger grounds out to the 'Reluctor', it will kill the module in a heart beat!

Also remember you need gauges to properly set up the Hall effect trigger.
It isn't like the Variable reluctor magnetic triggers in the rest of the electronic ignitions...
Modern magnetic triggers don't have line voltage running through them!

Last edited by JeepHammer; 09-14-2007 at 10:59 PM..
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Unread 09-15-2007, 12:47 PM   #11
Geer_hed
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Well that's a bit nightmarish... The install instrux did have some mention of depth gauging the trigger for efficient operation, but we unfortunately didn't have the tools necessary to event attempt it the evening I was over there.

While I have not been able to effectively steal any pics of the prestolite internals, essentially what you're saying is the sensor itself is electrified and could ground against the reluctor wheel (or the inside of the distributor itself I'm assuming)? That would make sense. He installed his own pickup coil evidently, and that was the rattling in the distributor, the wheel was striking the sensor on almost every pass

You mention the lack of a resistive wire in the prestolite setup, would that mean the Duraspark repair manual does not refer to prestolite as "solid state"?
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