Are you ready for a real weird one? Random NO spark from a MP electronic ignition system despite numerous parts swapped around...

[68 Sport Satellite]

I am going back to the beginning Greg. I don't have the time to read through 21 pages of comments to see if this has been mentioned or not. My new to me 64 Polara has Mopar electronic ignition on it and I am experiencing a similar no start condition like you. You can jumper the coil + terminal from the battery + and it will start. The voltage drop while cranking goes down to 10.9 and 10.8 at the ECU. I am wondering what the minimum voltage is for the ECU's. I need to do a little testing. Does it have spark after a battery charge when the surface voltage is around 13v. or so? Could I provide an external 12 v power source for the ECU and the car would start? This theory is all about the starter draw pulling the battery down below the minimum operating voltage of the ECU. @Dave6T4 mentioned that he replaced his old starter with a new style Nippon Denso and not only did it spin over faster, the car started easier. Like he said
"I think the old starter was pulling so much power, there was not much left for ignition system." I think he might be onto something. I might try the battery charge test first just to see what happens. If low voltage is the issue, a stronger battery sure could help. So could a news starter. Even a different ECU that isn't as picky about minimum voltage may fix the issue. I may end up going back to a plain old single point distributor with a Pertronix in it.

I've also had a mini-starter go bad after a few years and it would drain the battery and cause starting issues. I finally took it to my ace mechanic who is excellent at tracing electrical issues and he traced it to a short in the starter. Replaced that starter with another mini starter and its been fine ever since.

 

[mbc0724]

I rarely get simple problems to post about. I get the weird ones that test my skills and patience.
This car:

View attachment 1633388

Has a 440 based 493 with mostly aftermarket stuff on it. It was a 318 model so when I did my first 440 swap to it in 2001, I converted it to the then popular Mopar Performance electronic conversion kit. The distributors they used for this were physically similar to the stock electronic distributors from the outside but had Mallory internals scaled down to fit a Chrysler housing. Smaller advance weights, lighter springs and generally not that great. They get spark scatter, unstable timing and can cause erratic idle issues. I worked though most of that so this one performs okay.
Here is the ongoing issue that I've encountered several times since around 2012, giver or take:
It could be a cold start or a warm restart....I get no spark. None. I touched nothing, I moved nothing, it just started and ran normally moments or days earlier and now it spins and won't fire. Sometimes I've changed the ECM and it starts fine immediately afterwards so I blamed the ECM since we all know the spotty reliability of the Orange box...

View attachment 1633389

Once I was at the Sacramento Autorama on display and it was the day to take our cars and leave. No spark, no tools, no spare parts. I twisted connections, wiggled wires and cussed a lot. Nothing helped. About an hour of screwing around, then I sat inside and tried again and BOOM, it fired up like normal.

Weeks afterward, a car club member offered to help me rewire the engine side to avoid future NO start issues. It started fine before he worked his magic. Afterwards I had the NO spark again along with some funky headlight door reactions. (That I figured out some 10 years later when I installed the CrackedBack headlight relays!) I gave up and ordered a new harness from Evans.

Randomly over the years, it has happened, almost every time here at home, thank the Lord for that at least. I've tried bypassing the ignition switch with a spare one attached from under the dash. No change, still NO spark.
I've tried Ether/Starting fluid with mixed results. Sometimes it fires up immediately but I wonder if that was just how the damned thing is....maybe the ether spray made no difference and it was going to start when it was ready no matter what.

In 2017 I wanted to weigh the car and I had to get home (In my work truck) in time to get the Charger to the scales. One time it stalled without reason at an intersection and after trying a new coil then ECM, it fired up. The next day, It stalled in my driveway and putting the previous coil back in allowed it to start.
Yeah...It has been musical chairs with parts.
A couple of weeks ago I was tinkering with the A/C and pulled the low pressure switch. The car stalled and shut off. NO spark again. Why? What the heck does the low pressure switch have to do with the ignition wiring? I swapped in another ECM and it started up.

It feels as if I'm on the receiving end of some voodoo curse, like some "force" is watching me and selecting specific parts to conk out and stall the car, then just allowing it to start up again. Yeah, I know that is impossible, it just seems really strange.

I've adjusted the distributor air gap as per the FSM and other publications. .008 set with a brass feeler gage.
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EDIT:
Sometimes it will feel like it wants to start as I turn the key back to LOCK.

Thanks--sounds a lot like the issue that just started for me. Your headlight door comment also caught my attention--last week for no apparent reason the doors stopped working. I rarely drive at night so I was not too concerned. I just lowered them manually and figured I'd get to it when I get to it. I didn't think it was anything other than a coincidence when this issue started a day or two later!

 

[68 Sport Satellite]

@Kern Dog - since your install of the new battery, would you call your electrical no spark issue at the ECU now solved or is the electrical system still showing signs of non-ideal behaviour?

 

[Kern Dog]

Since I changed the battery, I have been swamped with other things here to do.
Rich and I have been working on rebuilding the engines in these cars...

I've been working with my nephew building a Go Cart...

Of course this place needs maintenance too....

The car has started consistently though since I moved the battery back up front and switched to this Lithium one.

 

[Kern Dog]

Sorry, Mike. I missed this one from you.

I am going back to the beginning Greg. I don't have the time to read through 21 pages of comments to see if this has been mentioned or not. My new to me 64 Polara has Mopar electronic ignition on it and I am experiencing a similar no start condition like you. You can jumper the coil + terminal from the battery + and it will start. The voltage drop while cranking goes down to 10.9 and 10.8 at the ECU. I am wondering what the minimum voltage is for the ECU's. I need to do a little testing. Does it have spark after a battery charge when the surface voltage is around 13v. or so? Could I provide an external 12 v power source for the ECU and the car would start? This theory is all about the starter draw pulling the battery down below the minimum operating voltage of the ECU. @Dave6T4 mentioned that he replaced his old starter with a new style Nippon Denso and not only did it spin over faster, the car started easier. Like he said
"I think the old starter was pulling so much power, there was not much left for ignition system." I think he might be onto something. I might try the battery charge test first just to see what happens. If low voltage is the issue, a stronger battery sure could help. So could a news starter. Even a different ECU that isn't as picky about minimum voltage may fix the issue. I may end up going back to a plain old single point distributor with a Pertronix in it.

That condition of where the low battery voltage possibly leading to ECU/Spark issues may be a real thing. The battery could be just charged enough to start the car but not have enough reserve if the carburetor were dry. If it started within 15 seconds, the battery would still be pulling a lot of juice to be recharged and I wonder if that somehow exposed a weak link in the ignition system.
I am just operating on theory though. I'd need someone more skilled with ignition systems than ME to feel more confident about it.