Ignition module failures

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canyncarvr

canyncarvr

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The last two I've bothered looking at after they quit had at least one similar symptom: The distributor + pin measured short to ground (case).

I'm curious to what extent others have found that to be true. Anyone bother looking at failed modules with a meter to maybe find the same issue?

Thanks for the input!
 
canyncarvr said:
The last two I've bothered looking at after they quit had at least one similar symptom: The distributor + pin measured short to ground (case).

I'm curious to what extent others have found that to be true. Anyone bother looking at failed modules with a meter to maybe find the same issue?

Thanks for the input!
Click to expand...
I haven't looked at the circuit diagrams. Not even sure I'd fully understand them. Distributor wires are simply pulse signals that are amplified. I think that's the big transistor.
There's at least one general explanation and photo of the circuit board in the master tech series. Probably for the 5 pin version but same concept.
Here's one: 1972 Imperial & Chrysler Ignition System Service Book (Session 292)

The only person I know of whose delved into the failures and publicly posted them is Nacho on Moparts, FABO and Dodgecharger.
Text has survived even though his pics have not.
Working on fix ECUs... AND FIXING WITH SUCCESS!!!
 
Thousands and thousands of original OEM Mopar modules ran long enough to make it to the junk yard. I've run a few that came from there, and still have some (somewhere) that are likely good

Are these failed modules FOR SURE OEM "old school" IE not "more modern" chinese/ etc replacements?

How are you running them, that is, proper ballast, or a high performance coil / ballast combo?
 
Following up on my comment earlier, the booklet says the big transistor on the outside handles switching power to the coil on and off. That is grounded. I don't know how that is tied to the signal amplifier, but a mismatched coil and resister could let too much current through.
 
I can guess a few problems for failure.
1. Spark plug cable, or coil to cap cable intertwined with distributor pickup cable.
2. Intermittent ground at module.
3. No ballast resistor, resulting in high peak current, and main transistor failure. It would also show short on lead that goes to ignition coil (-).

My guess would be 2, loss of ground during ignition event, may result in undesirable path of high voltage, finding ground via pick up coil breakdown to distributor. That event would likely short transistor at pickup +.
 
67Dart273 said:
Are these failed modules FOR SURE OEM "old school" IE not "more modern" chinese/ etc replacements?

How are you running them, that is, proper ballast, or a high performance coil / ballast combo?
Click to expand...

The one failure I had 'in use' was NOT a 'for sure' unit. Not sure where it came from. It was on the fender for years doing nothing when I was running my MSD box. The second failure was DOA..some supposed NOS (NOT Mopar) piece.

'Proper' ballast. They do vary in actual measurement, but something along the line of an RU12. I've run an Accel 140001 for over 30 years. Ran it with my MSD-6C for years, too (w/ no ballast).

I'm not looking to solve a problem. I've had only one or two Chrysler modules go bad in 45 years.

I am curious how many of them fail in the same way...dist+ to ground short.
 
My guess is most change parts till they fix it, only a few trouble shoot like you have done, at pin level. So the history does not exist.

The no ballast with MSD is different, the coil is used as a transformer, pulsed with high voltage capacitor.

I missed Del's and Mattax posts prior to my post, but we share idea of too much coil current, that limit is set by sum of ballast and coil resistance.
 
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Again...not looking to fix anything. I am aware that a good ground is a necessity, but that's a problem that doesn't need to be solved here.
 
KitCarlson said:
My guess is most change parts till they fix it, only a few trouble shoot like you have done, at pin level. So the history does not exist.

The no ballast with MSD is different, the coil is used as a transformer, pulsed with high voltage capacitor.

I missed Del's and Mattax posts prior to my post, but we share idea of too much coil current, that limit is set by sum of ballast and coil resistance.
Click to expand...

Hi Dave, how the heck, are ya?
 
canyncarvr said:
T I've run an Accel 140001 for over 30 years. Ran it with my MSD-6C for years, too (w/ no ballast).

I
Click to expand...

Just for info, MSD is a completely different mule of a different color. There is NO DC (battery) current through the coil with a CD/ MSD. The MSD generates a high voltage pulse sort of like a photoflash, and the trigger device (points or distributor) causes the box to discharge across the coil. This, in part, is why you cannot hook a tach to an MSD driven coil. Most CD setups/ MSD, also, the coil NEG is grounded. What some of us call "switching" type systems, like Mopar ECU, Pertronix, GM HEI and others, work more like points.........they swtich the coil NEG on/ off with battery supplied to the coil +
 
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