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Driving around yesterday - M37 was running like a swiss watch. Stopped somewhere for a few hours. When I went to start the truck, she'd crank, but there was no spark at the plugs. Of course, it was getting cold and dark, and snowing furiously. (This never seems to happen on nice days). Also my voltmeter has brand new batteries - and was sitting on my kitchen table (duh!).
Flipped the ignition switch on & off many times, checked the wiring (as much as I could without a voltmeter). Had fuel & air, just no spark at any of the plugs. Got a free flat-bed ride home from AAA.
At first, I'm thinking coil, distributor cap, or ignition switch problem. I have the PAMCO ignition kit, and a rock solid charging system. Wiring harness less than 10 years old.
Go to troubleshoot this morning - she fires right up. No hesitation, no hiccoughs, as if nothing had happened. Tried to reproduce the problem, but it keeps staring. (When was the last time that you had THAT problem?)
I tried wiggling every wire from ignition switch to distributor while the truck was running. No problems there. So, any thoughts? What would cause a short-term lack of spark that spontaneously fixes itself?

Hi N1,

Just being Devil's advocate here......how did you know you had fuel, but no spark? Are you running the original ignition switch with the Douglas connectors or the later Packard style.....or something else?
The early Douglas style is notorious for cracking and failing.

regards,
bob

probably a bad coil but could also be the distributor. I'm leaning coil though because they can do some weird stuff when they start going bad

Good question - I could smell it in the carb after far too much cranking. The ignition switch has Packard connectors, and all connectors have dielectric grease on them.

w30bob wrote:Hi N1,

Just being Devil's advocate here......how did you know you had fuel, but no spark? Are you running the original ignition switch with the Douglas connectors or the later Packard style.....or something else?
The early Douglas style is notorious for cracking and failing.

regards,
bob

Hmm - that's what I was thinking. Good thing I have a spare coil. Too bad it was in my basement when I broke down.

tbone1004 wrote:probably a bad coil but could also be the distributor. I'm leaning coil though because they can do some weird stuff when they start going bad

Hi N1,

Another thing to check while you've got the distributor cover of is to look for signs of condensation. You said it ran all day, you parked it, and then it wouldn't start. So it was hot, cooled off, and wouldn't start. Moisture under the cap could also cause an electrical problem. Just thinking out loud here.

regards,
bob

Long overdue followup. Drumroll please ...
The coil was the problem! Changed it out. Now it starts right up & runs like a champ.
Thanks all.